linux_dsm_epyc7002/drivers/gpu/drm/i915/i915_perf.c

/*
 * Copyright © 2015-2016 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 * Authors:
 *   Robert Bragg <robert@sixbynine.org>
 */


/**
 * DOC: i915 Perf Overview
 *
 * Gen graphics supports a large number of performance counters that can help
 * driver and application developers understand and optimize their use of the
 * GPU.
 *
 * This i915 perf interface enables userspace to configure and open a file
 * descriptor representing a stream of GPU metrics which can then be read() as
 * a stream of sample records.
 *
 * The interface is particularly suited to exposing buffered metrics that are
 * captured by DMA from the GPU, unsynchronized with and unrelated to the CPU.
 *
 * Streams representing a single context are accessible to applications with a
 * corresponding drm file descriptor, such that OpenGL can use the interface
 * without special privileges. Access to system-wide metrics requires root
 * privileges by default, unless changed via the dev.i915.perf_event_paranoid
 * sysctl option.
 *
 */

/**
 * DOC: i915 Perf History and Comparison with Core Perf
 *
 * The interface was initially inspired by the core Perf infrastructure but
 * some notable differences are:
 *
 * i915 perf file descriptors represent a "stream" instead of an "event"; where
 * a perf event primarily corresponds to a single 64bit value, while a stream
 * might sample sets of tightly-coupled counters, depending on the
 * configuration.  For example the Gen OA unit isn't designed to support
 * orthogonal configurations of individual counters; it's configured for a set
 * of related counters. Samples for an i915 perf stream capturing OA metrics
 * will include a set of counter values packed in a compact HW specific format.
 * The OA unit supports a number of different packing formats which can be
 * selected by the user opening the stream. Perf has support for grouping
 * events, but each event in the group is configured, validated and
 * authenticated individually with separate system calls.
 *
 * i915 perf stream configurations are provided as an array of u64 (key,value)
 * pairs, instead of a fixed struct with multiple miscellaneous config members,
 * interleaved with event-type specific members.
 *
 * i915 perf doesn't support exposing metrics via an mmap'd circular buffer.
 * The supported metrics are being written to memory by the GPU unsynchronized
 * with the CPU, using HW specific packing formats for counter sets. Sometimes
 * the constraints on HW configuration require reports to be filtered before it
 * would be acceptable to expose them to unprivileged applications - to hide
 * the metrics of other processes/contexts. For these use cases a read() based
 * interface is a good fit, and provides an opportunity to filter data as it
 * gets copied from the GPU mapped buffers to userspace buffers.
 *
 *
 * Issues hit with first prototype based on Core Perf
 * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 *
 * The first prototype of this driver was based on the core perf
 * infrastructure, and while we did make that mostly work, with some changes to
 * perf, we found we were breaking or working around too many assumptions baked
 * into perf's currently cpu centric design.
 *
 * In the end we didn't see a clear benefit to making perf's implementation and
 * interface more complex by changing design assumptions while we knew we still
 * wouldn't be able to use any existing perf based userspace tools.
 *
 * Also considering the Gen specific nature of the Observability hardware and
 * how userspace will sometimes need to combine i915 perf OA metrics with
 * side-band OA data captured via MI_REPORT_PERF_COUNT commands; we're
 * expecting the interface to be used by a platform specific userspace such as
 * OpenGL or tools. This is to say; we aren't inherently missing out on having
 * a standard vendor/architecture agnostic interface by not using perf.
 *
 *
 * For posterity, in case we might re-visit trying to adapt core perf to be
 * better suited to exposing i915 metrics these were the main pain points we
 * hit:
 *
 * - The perf based OA PMU driver broke some significant design assumptions:
 *
 *   Existing perf pmus are used for profiling work on a cpu and we were
 *   introducing the idea of _IS_DEVICE pmus with different security
 *   implications, the need to fake cpu-related data (such as user/kernel
 *   registers) to fit with perf's current design, and adding _DEVICE records
 *   as a way to forward device-specific status records.
 *
 *   The OA unit writes reports of counters into a circular buffer, without
 *   involvement from the CPU, making our PMU driver the first of a kind.
 *
 *   Given the way we were periodically forward data from the GPU-mapped, OA
 *   buffer to perf's buffer, those bursts of sample writes looked to perf like
 *   we were sampling too fast and so we had to subvert its throttling checks.
 *
 *   Perf supports groups of counters and allows those to be read via
 *   transactions internally but transactions currently seem designed to be
 *   explicitly initiated from the cpu (say in response to a userspace read())
 *   and while we could pull a report out of the OA buffer we can't
 *   trigger a report from the cpu on demand.
 *
 *   Related to being report based; the OA counters are configured in HW as a
 *   set while perf generally expects counter configurations to be orthogonal.
 *   Although counters can be associated with a group leader as they are
 *   opened, there's no clear precedent for being able to provide group-wide
 *   configuration attributes (for example we want to let userspace choose the
 *   OA unit report format used to capture all counters in a set, or specify a
 *   GPU context to filter metrics on). We avoided using perf's grouping
 *   feature and forwarded OA reports to userspace via perf's 'raw' sample
 *   field. This suited our userspace well considering how coupled the counters
 *   are when dealing with normalizing. It would be inconvenient to split
 *   counters up into separate events, only to require userspace to recombine
 *   them. For Mesa it's also convenient to be forwarded raw, periodic reports
 *   for combining with the side-band raw reports it captures using
 *   MI_REPORT_PERF_COUNT commands.
 *
 *   - As a side note on perf's grouping feature; there was also some concern
 *     that using PERF_FORMAT_GROUP as a way to pack together counter values
 *     would quite drastically inflate our sample sizes, which would likely
 *     lower the effective sampling resolutions we could use when the available
 *     memory bandwidth is limited.
 *
 *     With the OA unit's report formats, counters are packed together as 32
 *     or 40bit values, with the largest report size being 256 bytes.
 *
 *     PERF_FORMAT_GROUP values are 64bit, but there doesn't appear to be a
 *     documented ordering to the values, implying PERF_FORMAT_ID must also be
 *     used to add a 64bit ID before each value; giving 16 bytes per counter.
 *
 *   Related to counter orthogonality; we can't time share the OA unit, while
 *   event scheduling is a central design idea within perf for allowing
 *   userspace to open + enable more events than can be configured in HW at any
 *   one time.  The OA unit is not designed to allow re-configuration while in
 *   use. We can't reconfigure the OA unit without losing internal OA unit
 *   state which we can't access explicitly to save and restore. Reconfiguring
 *   the OA unit is also relatively slow, involving ~100 register writes. From
 *   userspace Mesa also depends on a stable OA configuration when emitting
 *   MI_REPORT_PERF_COUNT commands and importantly the OA unit can't be
 *   disabled while there are outstanding MI_RPC commands lest we hang the
 *   command streamer.
 *
 *   The contents of sample records aren't extensible by device drivers (i.e.
 *   the sample_type bits). As an example; Sourab Gupta had been looking to
 *   attach GPU timestamps to our OA samples. We were shoehorning OA reports
 *   into sample records by using the 'raw' field, but it's tricky to pack more
 *   than one thing into this field because events/core.c currently only lets a
 *   pmu give a single raw data pointer plus len which will be copied into the
 *   ring buffer. To include more than the OA report we'd have to copy the
 *   report into an intermediate larger buffer. I'd been considering allowing a
 *   vector of data+len values to be specified for copying the raw data, but
 *   it felt like a kludge to being using the raw field for this purpose.
 *
 * - It felt like our perf based PMU was making some technical compromises
 *   just for the sake of using perf:
 *
 *   perf_event_open() requires events to either relate to a pid or a specific
 *   cpu core, while our device pmu related to neither.  Events opened with a
 *   pid will be automatically enabled/disabled according to the scheduling of
 *   that process - so not appropriate for us. When an event is related to a
 *   cpu id, perf ensures pmu methods will be invoked via an inter process
 *   interrupt on that core. To avoid invasive changes our userspace opened OA
 *   perf events for a specific cpu. This was workable but it meant the
 *   majority of the OA driver ran in atomic context, including all OA report
 *   forwarding, which wasn't really necessary in our case and seems to make
 *   our locking requirements somewhat complex as we handled the interaction
 *   with the rest of the i915 driver.
 */

#include <linux/anon_inodes.h>
#include <linux/sizes.h>

#include "i915_drv.h"
#include "i915_oa_hsw.h"

/* HW requires this to be a power of two, between 128k and 16M, though driver
 * is currently generally designed assuming the largest 16M size is used such
 * that the overflow cases are unlikely in normal operation.
 */
#define OA_BUFFER_SIZE		SZ_16M

#define OA_TAKEN(tail, head)	((tail - head) & (OA_BUFFER_SIZE - 1))

/* There's a HW race condition between OA unit tail pointer register updates and
 * writes to memory whereby the tail pointer can sometimes get ahead of what's
 * been written out to the OA buffer so far.
 *
 * Although this can be observed explicitly by checking for a zeroed report-id
 * field in tail reports, it seems preferable to account for this earlier e.g.
 * as part of the _oa_buffer_is_empty checks to minimize -EAGAIN polling cycles
 * in this situation.
 *
 * To give time for the most recent reports to land before they may be copied to
 * userspace, the driver operates as if the tail pointer effectively lags behind
 * the HW tail pointer by 'tail_margin' bytes. The margin in bytes is calculated
 * based on this constant in nanoseconds, the current OA sampling exponent
 * and current report size.
 *
 * There is also a fallback check while reading to simply skip over reports with
 * a zeroed report-id.
 */
#define OA_TAIL_MARGIN_NSEC	100000ULL

/* frequency for checking whether the OA unit has written new reports to the
 * circular OA buffer...
 */
#define POLL_FREQUENCY 200
#define POLL_PERIOD (NSEC_PER_SEC / POLL_FREQUENCY)

/* for sysctl proc_dointvec_minmax of dev.i915.perf_stream_paranoid */
static int zero;
static int one = 1;
static u32 i915_perf_stream_paranoid = true;

/* The maximum exponent the hardware accepts is 63 (essentially it selects one
 * of the 64bit timestamp bits to trigger reports from) but there's currently
 * no known use case for sampling as infrequently as once per 47 thousand years.
 *
 * Since the timestamps included in OA reports are only 32bits it seems
 * reasonable to limit the OA exponent where it's still possible to account for
 * overflow in OA report timestamps.
 */
#define OA_EXPONENT_MAX 31

#define INVALID_CTX_ID 0xffffffff


/* For sysctl proc_dointvec_minmax of i915_oa_max_sample_rate
 *
 * 160ns is the smallest sampling period we can theoretically program the OA
 * unit with on Haswell, corresponding to 6.25MHz.
 */
static int oa_sample_rate_hard_limit = 6250000;

/* Theoretically we can program the OA unit to sample every 160ns but don't
 * allow that by default unless root...
 *
 * The default threshold of 100000Hz is based on perf's similar
 * kernel.perf_event_max_sample_rate sysctl parameter.
 */
static u32 i915_oa_max_sample_rate = 100000;

/* XXX: beware if future OA HW adds new report formats that the current
 * code assumes all reports have a power-of-two size and ~(size - 1) can
 * be used as a mask to align the OA tail pointer.
 */
static struct i915_oa_format hsw_oa_formats[I915_OA_FORMAT_MAX] = {
	[I915_OA_FORMAT_A13]	    = { 0, 64 },
	[I915_OA_FORMAT_A29]	    = { 1, 128 },
	[I915_OA_FORMAT_A13_B8_C8]  = { 2, 128 },
	/* A29_B8_C8 Disallowed as 192 bytes doesn't factor into buffer size */
	[I915_OA_FORMAT_B4_C8]	    = { 4, 64 },
	[I915_OA_FORMAT_A45_B8_C8]  = { 5, 256 },
	[I915_OA_FORMAT_B4_C8_A16]  = { 6, 128 },
	[I915_OA_FORMAT_C4_B8]	    = { 7, 64 },
};

#define SAMPLE_OA_REPORT      (1<<0)

/**
 * struct perf_open_properties - for validated properties given to open a stream
 * @sample_flags: `DRM_I915_PERF_PROP_SAMPLE_*` properties are tracked as flags
 * @single_context: Whether a single or all gpu contexts should be monitored
 * @ctx_handle: A gem ctx handle for use with @single_context
 * @metrics_set: An ID for an OA unit metric set advertised via sysfs
 * @oa_format: An OA unit HW report format
 * @oa_periodic: Whether to enable periodic OA unit sampling
 * @oa_period_exponent: The OA unit sampling period is derived from this
 *
 * As read_properties_unlocked() enumerates and validates the properties given
 * to open a stream of metrics the configuration is built up in the structure
 * which starts out zero initialized.
 */
struct perf_open_properties {
	u32 sample_flags;

	u64 single_context:1;
	u64 ctx_handle;

	/* OA sampling state */
	int metrics_set;
	int oa_format;
	bool oa_periodic;
	int oa_period_exponent;
};

/* NB: This is either called via fops or the poll check hrtimer (atomic ctx)
 *
 * It's safe to read OA config state here unlocked, assuming that this is only
 * called while the stream is enabled, while the global OA configuration can't
 * be modified.
 *
 * Note: we don't lock around the head/tail reads even though there's the slim
 * possibility of read() fop errors forcing a re-init of the OA buffer
 * pointers.  A race here could result in a false positive !empty status which
 * is acceptable.
 */
static bool gen7_oa_buffer_is_empty_fop_unlocked(struct drm_i915_private *dev_priv)
{
	int report_size = dev_priv->perf.oa.oa_buffer.format_size;
	u32 oastatus2 = I915_READ(GEN7_OASTATUS2);
	u32 oastatus1 = I915_READ(GEN7_OASTATUS1);
	u32 head = oastatus2 & GEN7_OASTATUS2_HEAD_MASK;
	u32 tail = oastatus1 & GEN7_OASTATUS1_TAIL_MASK;

	return OA_TAKEN(tail, head) <
		dev_priv->perf.oa.tail_margin + report_size;
}

/**
 * append_oa_status - Appends a status record to a userspace read() buffer.
 * @stream: An i915-perf stream opened for OA metrics
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @offset: (inout): the current position for writing into @buf
 * @type: The kind of status to report to userspace
 *
 * Writes a status record (such as `DRM_I915_PERF_RECORD_OA_REPORT_LOST`)
 * into the userspace read() buffer.
 *
 * The @buf @offset will only be updated on success.
 *
 * Returns: 0 on success, negative error code on failure.
 */
static int append_oa_status(struct i915_perf_stream *stream,
			    char __user *buf,
			    size_t count,
			    size_t *offset,
			    enum drm_i915_perf_record_type type)
{
	struct drm_i915_perf_record_header header = { type, 0, sizeof(header) };

	if ((count - *offset) < header.size)
		return -ENOSPC;

	if (copy_to_user(buf + *offset, &header, sizeof(header)))
		return -EFAULT;

	(*offset) += header.size;

	return 0;
}

/**
 * append_oa_sample - Copies single OA report into userspace read() buffer.
 * @stream: An i915-perf stream opened for OA metrics
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @offset: (inout): the current position for writing into @buf
 * @report: A single OA report to (optionally) include as part of the sample
 *
 * The contents of a sample are configured through `DRM_I915_PERF_PROP_SAMPLE_*`
 * properties when opening a stream, tracked as `stream->sample_flags`. This
 * function copies the requested components of a single sample to the given
 * read() @buf.
 *
 * The @buf @offset will only be updated on success.
 *
 * Returns: 0 on success, negative error code on failure.
 */
static int append_oa_sample(struct i915_perf_stream *stream,
			    char __user *buf,
			    size_t count,
			    size_t *offset,
			    const u8 *report)
{
	struct drm_i915_private *dev_priv = stream->dev_priv;
	int report_size = dev_priv->perf.oa.oa_buffer.format_size;
	struct drm_i915_perf_record_header header;
	u32 sample_flags = stream->sample_flags;

	header.type = DRM_I915_PERF_RECORD_SAMPLE;
	header.pad = 0;
	header.size = stream->sample_size;

	if ((count - *offset) < header.size)
		return -ENOSPC;

	buf += *offset;
	if (copy_to_user(buf, &header, sizeof(header)))
		return -EFAULT;
	buf += sizeof(header);

	if (sample_flags & SAMPLE_OA_REPORT) {
		if (copy_to_user(buf, report, report_size))
			return -EFAULT;
	}

	(*offset) += header.size;

	return 0;
}

/**
 * Copies all buffered OA reports into userspace read() buffer.
 * @stream: An i915-perf stream opened for OA metrics
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @offset: (inout): the current position for writing into @buf
 * @head_ptr: (inout): the current oa buffer cpu read position
 * @tail: the current oa buffer gpu write position
 *
 * Notably any error condition resulting in a short read (-%ENOSPC or
 * -%EFAULT) will be returned even though one or more records may
 * have been successfully copied. In this case it's up to the caller
 * to decide if the error should be squashed before returning to
 * userspace.
 *
 * Note: reports are consumed from the head, and appended to the
 * tail, so the head chases the tail?... If you think that's mad
 * and back-to-front you're not alone, but this follows the
 * Gen PRM naming convention.
 *
 * Returns: 0 on success, negative error code on failure.
 */
static int gen7_append_oa_reports(struct i915_perf_stream *stream,
				  char __user *buf,
				  size_t count,
				  size_t *offset,
				  u32 *head_ptr,
				  u32 tail)
{
	struct drm_i915_private *dev_priv = stream->dev_priv;
	int report_size = dev_priv->perf.oa.oa_buffer.format_size;
	u8 *oa_buf_base = dev_priv->perf.oa.oa_buffer.vaddr;
	int tail_margin = dev_priv->perf.oa.tail_margin;
	u32 gtt_offset = i915_ggtt_offset(dev_priv->perf.oa.oa_buffer.vma);
	u32 mask = (OA_BUFFER_SIZE - 1);
	u32 head;
	u32 taken;
	int ret = 0;

	if (WARN_ON(!stream->enabled))
		return -EIO;

	head = *head_ptr - gtt_offset;
	tail -= gtt_offset;

	/* The OA unit is expected to wrap the tail pointer according to the OA
	 * buffer size and since we should never write a misaligned head
	 * pointer we don't expect to read one back either...
	 */
	if (tail > OA_BUFFER_SIZE || head > OA_BUFFER_SIZE ||
	    head % report_size) {
		DRM_ERROR("Inconsistent OA buffer pointer (head = %u, tail = %u): force restart\n",
			  head, tail);
		dev_priv->perf.oa.ops.oa_disable(dev_priv);
		dev_priv->perf.oa.ops.oa_enable(dev_priv);
		*head_ptr = I915_READ(GEN7_OASTATUS2) &
			GEN7_OASTATUS2_HEAD_MASK;
		return -EIO;
	}


	/* The tail pointer increases in 64 byte increments, not in report_size
	 * steps...
	 */
	tail &= ~(report_size - 1);

	/* Move the tail pointer back by the current tail_margin to account for
	 * the possibility that the latest reports may not have really landed
	 * in memory yet...
	 */

	if (OA_TAKEN(tail, head) < report_size + tail_margin)
		return -EAGAIN;

	tail -= tail_margin;
	tail &= mask;

	for (/* none */;
	     (taken = OA_TAKEN(tail, head));
	     head = (head + report_size) & mask) {
		u8 *report = oa_buf_base + head;
		u32 *report32 = (void *)report;

		/* All the report sizes factor neatly into the buffer
		 * size so we never expect to see a report split
		 * between the beginning and end of the buffer.
		 *
		 * Given the initial alignment check a misalignment
		 * here would imply a driver bug that would result
		 * in an overrun.
		 */
		if (WARN_ON((OA_BUFFER_SIZE - head) < report_size)) {
			DRM_ERROR("Spurious OA head ptr: non-integral report offset\n");
			break;
		}

		/* The report-ID field for periodic samples includes
		 * some undocumented flags related to what triggered
		 * the report and is never expected to be zero so we
		 * can check that the report isn't invalid before
		 * copying it to userspace...
		 */
		if (report32[0] == 0) {
			DRM_NOTE("Skipping spurious, invalid OA report\n");
			continue;
		}

		ret = append_oa_sample(stream, buf, count, offset, report);
		if (ret)
			break;

		/* The above report-id field sanity check is based on
		 * the assumption that the OA buffer is initially
		 * zeroed and we reset the field after copying so the
		 * check is still meaningful once old reports start
		 * being overwritten.
		 */
		report32[0] = 0;
	}

	*head_ptr = gtt_offset + head;

	return ret;
}

/**
 * gen7_oa_read - copy status records then buffered OA reports
 * @stream: An i915-perf stream opened for OA metrics
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @offset: (inout): the current position for writing into @buf
 *
 * Checks Gen 7 specific OA unit status registers and if necessary appends
 * corresponding status records for userspace (such as for a buffer full
 * condition) and then initiate appending any buffered OA reports.
 *
 * Updates @offset according to the number of bytes successfully copied into
 * the userspace buffer.
 *
 * Returns: zero on success or a negative error code
 */
static int gen7_oa_read(struct i915_perf_stream *stream,
			char __user *buf,
			size_t count,
			size_t *offset)
{
	struct drm_i915_private *dev_priv = stream->dev_priv;
	int report_size = dev_priv->perf.oa.oa_buffer.format_size;
	u32 oastatus2;
	u32 oastatus1;
	u32 head;
	u32 tail;
	int ret;

	if (WARN_ON(!dev_priv->perf.oa.oa_buffer.vaddr))
		return -EIO;

	oastatus2 = I915_READ(GEN7_OASTATUS2);
	oastatus1 = I915_READ(GEN7_OASTATUS1);

	head = oastatus2 & GEN7_OASTATUS2_HEAD_MASK;
	tail = oastatus1 & GEN7_OASTATUS1_TAIL_MASK;

	/* XXX: On Haswell we don't have a safe way to clear oastatus1
	 * bits while the OA unit is enabled (while the tail pointer
	 * may be updated asynchronously) so we ignore status bits
	 * that have already been reported to userspace.
	 */
	oastatus1 &= ~dev_priv->perf.oa.gen7_latched_oastatus1;

	/* We treat OABUFFER_OVERFLOW as a significant error:
	 *
	 * - The status can be interpreted to mean that the buffer is
	 *   currently full (with a higher precedence than OA_TAKEN()
	 *   which will start to report a near-empty buffer after an
	 *   overflow) but it's awkward that we can't clear the status
	 *   on Haswell, so without a reset we won't be able to catch
	 *   the state again.
	 *
	 * - Since it also implies the HW has started overwriting old
	 *   reports it may also affect our sanity checks for invalid
	 *   reports when copying to userspace that assume new reports
	 *   are being written to cleared memory.
	 *
	 * - In the future we may want to introduce a flight recorder
	 *   mode where the driver will automatically maintain a safe
	 *   guard band between head/tail, avoiding this overflow
	 *   condition, but we avoid the added driver complexity for
	 *   now.
	 */
	if (unlikely(oastatus1 & GEN7_OASTATUS1_OABUFFER_OVERFLOW)) {
		ret = append_oa_status(stream, buf, count, offset,
				       DRM_I915_PERF_RECORD_OA_BUFFER_LOST);
		if (ret)
			return ret;

		DRM_DEBUG("OA buffer overflow: force restart\n");

		dev_priv->perf.oa.ops.oa_disable(dev_priv);
		dev_priv->perf.oa.ops.oa_enable(dev_priv);

		oastatus2 = I915_READ(GEN7_OASTATUS2);
		oastatus1 = I915_READ(GEN7_OASTATUS1);

		head = oastatus2 & GEN7_OASTATUS2_HEAD_MASK;
		tail = oastatus1 & GEN7_OASTATUS1_TAIL_MASK;
	}

	if (unlikely(oastatus1 & GEN7_OASTATUS1_REPORT_LOST)) {
		ret = append_oa_status(stream, buf, count, offset,
				       DRM_I915_PERF_RECORD_OA_REPORT_LOST);
		if (ret)
			return ret;
		dev_priv->perf.oa.gen7_latched_oastatus1 |=
			GEN7_OASTATUS1_REPORT_LOST;
	}

	ret = gen7_append_oa_reports(stream, buf, count, offset,
				     &head, tail);

	/* All the report sizes are a power of two and the
	 * head should always be incremented by some multiple
	 * of the report size.
	 *
	 * A warning here, but notably if we later read back a
	 * misaligned pointer we will treat that as a bug since
	 * it could lead to a buffer overrun.
	 */
	WARN_ONCE(head & (report_size - 1),
		  "i915: Writing misaligned OA head pointer");

	/* Note: we update the head pointer here even if an error
	 * was returned since the error may represent a short read
	 * where some some reports were successfully copied.
	 */
	I915_WRITE(GEN7_OASTATUS2,
		   ((head & GEN7_OASTATUS2_HEAD_MASK) |
		    OA_MEM_SELECT_GGTT));

	return ret;
}

/**
 * i915_oa_wait_unlocked - handles blocking IO until OA data available
 * @stream: An i915-perf stream opened for OA metrics
 *
 * Called when userspace tries to read() from a blocking stream FD opened
 * for OA metrics. It waits until the hrtimer callback finds a non-empty
 * OA buffer and wakes us.
 *
 * Note: it's acceptable to have this return with some false positives
 * since any subsequent read handling will return -EAGAIN if there isn't
 * really data ready for userspace yet.
 *
 * Returns: zero on success or a negative error code
 */
static int i915_oa_wait_unlocked(struct i915_perf_stream *stream)
{
	struct drm_i915_private *dev_priv = stream->dev_priv;

	/* We would wait indefinitely if periodic sampling is not enabled */
	if (!dev_priv->perf.oa.periodic)
		return -EIO;

	/* Note: the oa_buffer_is_empty() condition is ok to run unlocked as it
	 * just performs mmio reads of the OA buffer head + tail pointers and
	 * it's assumed we're handling some operation that implies the stream
	 * can't be destroyed until completion (such as a read()) that ensures
	 * the device + OA buffer can't disappear
	 */
	return wait_event_interruptible(dev_priv->perf.oa.poll_wq,
					!dev_priv->perf.oa.ops.oa_buffer_is_empty(dev_priv));
}

/**
 * i915_oa_poll_wait - call poll_wait() for an OA stream poll()
 * @stream: An i915-perf stream opened for OA metrics
 * @file: An i915 perf stream file
 * @wait: poll() state table
 *
 * For handling userspace polling on an i915 perf stream opened for OA metrics,
 * this starts a poll_wait with the wait queue that our hrtimer callback wakes
 * when it sees data ready to read in the circular OA buffer.
 */
static void i915_oa_poll_wait(struct i915_perf_stream *stream,
			      struct file *file,
			      poll_table *wait)
{
	struct drm_i915_private *dev_priv = stream->dev_priv;

	poll_wait(file, &dev_priv->perf.oa.poll_wq, wait);
}

/**
 * i915_oa_read - just calls through to &i915_oa_ops->read
 * @stream: An i915-perf stream opened for OA metrics
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @offset: (inout): the current position for writing into @buf
 *
 * Updates @offset according to the number of bytes successfully copied into
 * the userspace buffer.
 *
 * Returns: zero on success or a negative error code
 */
static int i915_oa_read(struct i915_perf_stream *stream,
			char __user *buf,
			size_t count,
			size_t *offset)
{
	struct drm_i915_private *dev_priv = stream->dev_priv;

	return dev_priv->perf.oa.ops.read(stream, buf, count, offset);
}

/**
 * oa_get_render_ctx_id - determine and hold ctx hw id
 * @stream: An i915-perf stream opened for OA metrics
 *
 * Determine the render context hw id, and ensure it remains fixed for the
 * lifetime of the stream. This ensures that we don't have to worry about
 * updating the context ID in OACONTROL on the fly.
 *
 * Returns: zero on success or a negative error code
 */
static int oa_get_render_ctx_id(struct i915_perf_stream *stream)
{
	struct drm_i915_private *dev_priv = stream->dev_priv;
	struct intel_engine_cs *engine = dev_priv->engine[RCS];
	int ret;

	ret = i915_mutex_lock_interruptible(&dev_priv->drm);
	if (ret)
		return ret;

	/* As the ID is the gtt offset of the context's vma we pin
	 * the vma to ensure the ID remains fixed.
	 *
	 * NB: implied RCS engine...
	 */
	ret = engine->context_pin(engine, stream->ctx);
	if (ret)
		goto unlock;

	/* Explicitly track the ID (instead of calling i915_ggtt_offset()
	 * on the fly) considering the difference with gen8+ and
	 * execlists
	 */
	dev_priv->perf.oa.specific_ctx_id =
		i915_ggtt_offset(stream->ctx->engine[engine->id].state);

unlock:
	mutex_unlock(&dev_priv->drm.struct_mutex);

	return ret;
}

/**
 * oa_put_render_ctx_id - counterpart to oa_get_render_ctx_id releases hold
 * @stream: An i915-perf stream opened for OA metrics
 *
 * In case anything needed doing to ensure the context HW ID would remain valid
 * for the lifetime of the stream, then that can be undone here.
 */
static void oa_put_render_ctx_id(struct i915_perf_stream *stream)
{
	struct drm_i915_private *dev_priv = stream->dev_priv;
	struct intel_engine_cs *engine = dev_priv->engine[RCS];

	mutex_lock(&dev_priv->drm.struct_mutex);

	dev_priv->perf.oa.specific_ctx_id = INVALID_CTX_ID;
	engine->context_unpin(engine, stream->ctx);

	mutex_unlock(&dev_priv->drm.struct_mutex);
}

static void
free_oa_buffer(struct drm_i915_private *i915)
{
	mutex_lock(&i915->drm.struct_mutex);

	i915_gem_object_unpin_map(i915->perf.oa.oa_buffer.vma->obj);
	i915_vma_unpin(i915->perf.oa.oa_buffer.vma);
	i915_gem_object_put(i915->perf.oa.oa_buffer.vma->obj);

	i915->perf.oa.oa_buffer.vma = NULL;
	i915->perf.oa.oa_buffer.vaddr = NULL;

	mutex_unlock(&i915->drm.struct_mutex);
}

static void i915_oa_stream_destroy(struct i915_perf_stream *stream)
{
	struct drm_i915_private *dev_priv = stream->dev_priv;

	BUG_ON(stream != dev_priv->perf.oa.exclusive_stream);

	dev_priv->perf.oa.ops.disable_metric_set(dev_priv);

	free_oa_buffer(dev_priv);

	intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);
	intel_runtime_pm_put(dev_priv);

	if (stream->ctx)
		oa_put_render_ctx_id(stream);

	dev_priv->perf.oa.exclusive_stream = NULL;
}

static void gen7_init_oa_buffer(struct drm_i915_private *dev_priv)
{
	u32 gtt_offset = i915_ggtt_offset(dev_priv->perf.oa.oa_buffer.vma);

	/* Pre-DevBDW: OABUFFER must be set with counters off,
	 * before OASTATUS1, but after OASTATUS2
	 */
	I915_WRITE(GEN7_OASTATUS2, gtt_offset | OA_MEM_SELECT_GGTT); /* head */
	I915_WRITE(GEN7_OABUFFER, gtt_offset);
	I915_WRITE(GEN7_OASTATUS1, gtt_offset | OABUFFER_SIZE_16M); /* tail */

	/* On Haswell we have to track which OASTATUS1 flags we've
	 * already seen since they can't be cleared while periodic
	 * sampling is enabled.
	 */
	dev_priv->perf.oa.gen7_latched_oastatus1 = 0;

	/* NB: although the OA buffer will initially be allocated
	 * zeroed via shmfs (and so this memset is redundant when
	 * first allocating), we may re-init the OA buffer, either
	 * when re-enabling a stream or in error/reset paths.
	 *
	 * The reason we clear the buffer for each re-init is for the
	 * sanity check in gen7_append_oa_reports() that looks at the
	 * report-id field to make sure it's non-zero which relies on
	 * the assumption that new reports are being written to zeroed
	 * memory...
	 */
	memset(dev_priv->perf.oa.oa_buffer.vaddr, 0, OA_BUFFER_SIZE);

	/* Maybe make ->pollin per-stream state if we support multiple
	 * concurrent streams in the future.
	 */
	dev_priv->perf.oa.pollin = false;
}

static int alloc_oa_buffer(struct drm_i915_private *dev_priv)
{
	struct drm_i915_gem_object *bo;
	struct i915_vma *vma;
	int ret;

	if (WARN_ON(dev_priv->perf.oa.oa_buffer.vma))
		return -ENODEV;

	ret = i915_mutex_lock_interruptible(&dev_priv->drm);
	if (ret)
		return ret;

	BUILD_BUG_ON_NOT_POWER_OF_2(OA_BUFFER_SIZE);
	BUILD_BUG_ON(OA_BUFFER_SIZE < SZ_128K || OA_BUFFER_SIZE > SZ_16M);

	bo = i915_gem_object_create(dev_priv, OA_BUFFER_SIZE);
	if (IS_ERR(bo)) {
		DRM_ERROR("Failed to allocate OA buffer\n");
		ret = PTR_ERR(bo);
		goto unlock;
	}

	ret = i915_gem_object_set_cache_level(bo, I915_CACHE_LLC);
	if (ret)
		goto err_unref;

	/* PreHSW required 512K alignment, HSW requires 16M */
	vma = i915_gem_object_ggtt_pin(bo, NULL, 0, SZ_16M, 0);
	if (IS_ERR(vma)) {
		ret = PTR_ERR(vma);
		goto err_unref;
	}
	dev_priv->perf.oa.oa_buffer.vma = vma;

	dev_priv->perf.oa.oa_buffer.vaddr =
		i915_gem_object_pin_map(bo, I915_MAP_WB);
	if (IS_ERR(dev_priv->perf.oa.oa_buffer.vaddr)) {
		ret = PTR_ERR(dev_priv->perf.oa.oa_buffer.vaddr);
		goto err_unpin;
	}

	dev_priv->perf.oa.ops.init_oa_buffer(dev_priv);

	DRM_DEBUG_DRIVER("OA Buffer initialized, gtt offset = 0x%x, vaddr = %p\n",
			 i915_ggtt_offset(dev_priv->perf.oa.oa_buffer.vma),
			 dev_priv->perf.oa.oa_buffer.vaddr);

	goto unlock;

err_unpin:
	__i915_vma_unpin(vma);

err_unref:
	i915_gem_object_put(bo);

	dev_priv->perf.oa.oa_buffer.vaddr = NULL;
	dev_priv->perf.oa.oa_buffer.vma = NULL;

unlock:
	mutex_unlock(&dev_priv->drm.struct_mutex);
	return ret;
}

static void config_oa_regs(struct drm_i915_private *dev_priv,
			   const struct i915_oa_reg *regs,
			   int n_regs)
{
	int i;

	for (i = 0; i < n_regs; i++) {
		const struct i915_oa_reg *reg = regs + i;

		I915_WRITE(reg->addr, reg->value);
	}
}

static int hsw_enable_metric_set(struct drm_i915_private *dev_priv)
{
	int ret = i915_oa_select_metric_set_hsw(dev_priv);

	if (ret)
		return ret;

	I915_WRITE(GDT_CHICKEN_BITS, (I915_READ(GDT_CHICKEN_BITS) |
				      GT_NOA_ENABLE));

	/* PRM:
	 *
	 * OA unit is using “crclk” for its functionality. When trunk
	 * level clock gating takes place, OA clock would be gated,
	 * unable to count the events from non-render clock domain.
	 * Render clock gating must be disabled when OA is enabled to
	 * count the events from non-render domain. Unit level clock
	 * gating for RCS should also be disabled.
	 */
	I915_WRITE(GEN7_MISCCPCTL, (I915_READ(GEN7_MISCCPCTL) &
				    ~GEN7_DOP_CLOCK_GATE_ENABLE));
	I915_WRITE(GEN6_UCGCTL1, (I915_READ(GEN6_UCGCTL1) |
				  GEN6_CSUNIT_CLOCK_GATE_DISABLE));

	config_oa_regs(dev_priv, dev_priv->perf.oa.mux_regs,
		       dev_priv->perf.oa.mux_regs_len);

	/* It apparently takes a fairly long time for a new MUX
	 * configuration to be be applied after these register writes.
	 * This delay duration was derived empirically based on the
	 * render_basic config but hopefully it covers the maximum
	 * configuration latency.
	 *
	 * As a fallback, the checks in _append_oa_reports() to skip
	 * invalid OA reports do also seem to work to discard reports
	 * generated before this config has completed - albeit not
	 * silently.
	 *
	 * Unfortunately this is essentially a magic number, since we
	 * don't currently know of a reliable mechanism for predicting
	 * how long the MUX config will take to apply and besides
	 * seeing invalid reports we don't know of a reliable way to
	 * explicitly check that the MUX config has landed.
	 *
	 * It's even possible we've miss characterized the underlying
	 * problem - it just seems like the simplest explanation why
	 * a delay at this location would mitigate any invalid reports.
	 */
	usleep_range(15000, 20000);

	config_oa_regs(dev_priv, dev_priv->perf.oa.b_counter_regs,
		       dev_priv->perf.oa.b_counter_regs_len);

	return 0;
}

static void hsw_disable_metric_set(struct drm_i915_private *dev_priv)
{
	I915_WRITE(GEN6_UCGCTL1, (I915_READ(GEN6_UCGCTL1) &
				  ~GEN6_CSUNIT_CLOCK_GATE_DISABLE));
	I915_WRITE(GEN7_MISCCPCTL, (I915_READ(GEN7_MISCCPCTL) |
				    GEN7_DOP_CLOCK_GATE_ENABLE));

	I915_WRITE(GDT_CHICKEN_BITS, (I915_READ(GDT_CHICKEN_BITS) &
				      ~GT_NOA_ENABLE));
}

static void gen7_update_oacontrol_locked(struct drm_i915_private *dev_priv)
{
	lockdep_assert_held(&dev_priv->perf.hook_lock);

	if (dev_priv->perf.oa.exclusive_stream->enabled) {
		struct i915_gem_context *ctx =
			dev_priv->perf.oa.exclusive_stream->ctx;
		u32 ctx_id = dev_priv->perf.oa.specific_ctx_id;

		bool periodic = dev_priv->perf.oa.periodic;
		u32 period_exponent = dev_priv->perf.oa.period_exponent;
		u32 report_format = dev_priv->perf.oa.oa_buffer.format;

		I915_WRITE(GEN7_OACONTROL,
			   (ctx_id & GEN7_OACONTROL_CTX_MASK) |
			   (period_exponent <<
			    GEN7_OACONTROL_TIMER_PERIOD_SHIFT) |
			   (periodic ? GEN7_OACONTROL_TIMER_ENABLE : 0) |
			   (report_format << GEN7_OACONTROL_FORMAT_SHIFT) |
			   (ctx ? GEN7_OACONTROL_PER_CTX_ENABLE : 0) |
			   GEN7_OACONTROL_ENABLE);
	} else
		I915_WRITE(GEN7_OACONTROL, 0);
}

static void gen7_oa_enable(struct drm_i915_private *dev_priv)
{
	unsigned long flags;

	/* Reset buf pointers so we don't forward reports from before now.
	 *
	 * Think carefully if considering trying to avoid this, since it
	 * also ensures status flags and the buffer itself are cleared
	 * in error paths, and we have checks for invalid reports based
	 * on the assumption that certain fields are written to zeroed
	 * memory which this helps maintains.
	 */
	gen7_init_oa_buffer(dev_priv);

	spin_lock_irqsave(&dev_priv->perf.hook_lock, flags);
	gen7_update_oacontrol_locked(dev_priv);
	spin_unlock_irqrestore(&dev_priv->perf.hook_lock, flags);
}

/**
 * i915_oa_stream_enable - handle `I915_PERF_IOCTL_ENABLE` for OA stream
 * @stream: An i915 perf stream opened for OA metrics
 *
 * [Re]enables hardware periodic sampling according to the period configured
 * when opening the stream. This also starts a hrtimer that will periodically
 * check for data in the circular OA buffer for notifying userspace (e.g.
 * during a read() or poll()).
 */
static void i915_oa_stream_enable(struct i915_perf_stream *stream)
{
	struct drm_i915_private *dev_priv = stream->dev_priv;

	dev_priv->perf.oa.ops.oa_enable(dev_priv);

	if (dev_priv->perf.oa.periodic)
		hrtimer_start(&dev_priv->perf.oa.poll_check_timer,
			      ns_to_ktime(POLL_PERIOD),
			      HRTIMER_MODE_REL_PINNED);
}

static void gen7_oa_disable(struct drm_i915_private *dev_priv)
{
	I915_WRITE(GEN7_OACONTROL, 0);
}

/**
 * i915_oa_stream_disable - handle `I915_PERF_IOCTL_DISABLE` for OA stream
 * @stream: An i915 perf stream opened for OA metrics
 *
 * Stops the OA unit from periodically writing counter reports into the
 * circular OA buffer. This also stops the hrtimer that periodically checks for
 * data in the circular OA buffer, for notifying userspace.
 */
static void i915_oa_stream_disable(struct i915_perf_stream *stream)
{
	struct drm_i915_private *dev_priv = stream->dev_priv;

	dev_priv->perf.oa.ops.oa_disable(dev_priv);

	if (dev_priv->perf.oa.periodic)
		hrtimer_cancel(&dev_priv->perf.oa.poll_check_timer);
}

static u64 oa_exponent_to_ns(struct drm_i915_private *dev_priv, int exponent)
{
	return div_u64(1000000000ULL * (2ULL << exponent),
		       dev_priv->perf.oa.timestamp_frequency);
}

static const struct i915_perf_stream_ops i915_oa_stream_ops = {
	.destroy = i915_oa_stream_destroy,
	.enable = i915_oa_stream_enable,
	.disable = i915_oa_stream_disable,
	.wait_unlocked = i915_oa_wait_unlocked,
	.poll_wait = i915_oa_poll_wait,
	.read = i915_oa_read,
};

/**
 * i915_oa_stream_init - validate combined props for OA stream and init
 * @stream: An i915 perf stream
 * @param: The open parameters passed to `DRM_I915_PERF_OPEN`
 * @props: The property state that configures stream (individually validated)
 *
 * While read_properties_unlocked() validates properties in isolation it
 * doesn't ensure that the combination necessarily makes sense.
 *
 * At this point it has been determined that userspace wants a stream of
 * OA metrics, but still we need to further validate the combined
 * properties are OK.
 *
 * If the configuration makes sense then we can allocate memory for
 * a circular OA buffer and apply the requested metric set configuration.
 *
 * Returns: zero on success or a negative error code.
 */
static int i915_oa_stream_init(struct i915_perf_stream *stream,
			       struct drm_i915_perf_open_param *param,
			       struct perf_open_properties *props)
{
	struct drm_i915_private *dev_priv = stream->dev_priv;
	int format_size;
	int ret;

	/* If the sysfs metrics/ directory wasn't registered for some
	 * reason then don't let userspace try their luck with config
	 * IDs
	 */
	if (!dev_priv->perf.metrics_kobj) {
		DRM_DEBUG("OA metrics weren't advertised via sysfs\n");
		return -EINVAL;
	}

	if (!(props->sample_flags & SAMPLE_OA_REPORT)) {
		DRM_DEBUG("Only OA report sampling supported\n");
		return -EINVAL;
	}

	if (!dev_priv->perf.oa.ops.init_oa_buffer) {
		DRM_DEBUG("OA unit not supported\n");
		return -ENODEV;
	}

	/* To avoid the complexity of having to accurately filter
	 * counter reports and marshal to the appropriate client
	 * we currently only allow exclusive access
	 */
	if (dev_priv->perf.oa.exclusive_stream) {
		DRM_DEBUG("OA unit already in use\n");
		return -EBUSY;
	}

	if (!props->metrics_set) {
		DRM_DEBUG("OA metric set not specified\n");
		return -EINVAL;
	}

	if (!props->oa_format) {
		DRM_DEBUG("OA report format not specified\n");
		return -EINVAL;
	}

	stream->sample_size = sizeof(struct drm_i915_perf_record_header);

	format_size = dev_priv->perf.oa.oa_formats[props->oa_format].size;

	stream->sample_flags |= SAMPLE_OA_REPORT;
	stream->sample_size += format_size;

	dev_priv->perf.oa.oa_buffer.format_size = format_size;
	if (WARN_ON(dev_priv->perf.oa.oa_buffer.format_size == 0))
		return -EINVAL;

	dev_priv->perf.oa.oa_buffer.format =
		dev_priv->perf.oa.oa_formats[props->oa_format].format;

	dev_priv->perf.oa.metrics_set = props->metrics_set;

	dev_priv->perf.oa.periodic = props->oa_periodic;
	if (dev_priv->perf.oa.periodic) {
		u32 tail;

		dev_priv->perf.oa.period_exponent = props->oa_period_exponent;

		/* See comment for OA_TAIL_MARGIN_NSEC for details
		 * about this tail_margin...
		 */
		tail = div64_u64(OA_TAIL_MARGIN_NSEC,
				 oa_exponent_to_ns(dev_priv,
						   props->oa_period_exponent));
		dev_priv->perf.oa.tail_margin = (tail + 1) * format_size;
	}

	if (stream->ctx) {
		ret = oa_get_render_ctx_id(stream);
		if (ret)
			return ret;
	}

	ret = alloc_oa_buffer(dev_priv);
	if (ret)
		goto err_oa_buf_alloc;

	/* PRM - observability performance counters:
	 *
	 *   OACONTROL, performance counter enable, note:
	 *
	 *   "When this bit is set, in order to have coherent counts,
	 *   RC6 power state and trunk clock gating must be disabled.
	 *   This can be achieved by programming MMIO registers as
	 *   0xA094=0 and 0xA090[31]=1"
	 *
	 *   In our case we are expecting that taking pm + FORCEWAKE
	 *   references will effectively disable RC6.
	 */
	intel_runtime_pm_get(dev_priv);
	intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL);

	ret = dev_priv->perf.oa.ops.enable_metric_set(dev_priv);
	if (ret)
		goto err_enable;

	stream->ops = &i915_oa_stream_ops;

	dev_priv->perf.oa.exclusive_stream = stream;

	return 0;

err_enable:
	intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);
	intel_runtime_pm_put(dev_priv);
	free_oa_buffer(dev_priv);

err_oa_buf_alloc:
	if (stream->ctx)
		oa_put_render_ctx_id(stream);

	return ret;
}

/**
 * i915_perf_read_locked - &i915_perf_stream_ops->read with error normalisation
 * @stream: An i915 perf stream
 * @file: An i915 perf stream file
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @ppos: (inout) file seek position (unused)
 *
 * Besides wrapping &i915_perf_stream_ops->read this provides a common place to
 * ensure that if we've successfully copied any data then reporting that takes
 * precedence over any internal error status, so the data isn't lost.
 *
 * For example ret will be -ENOSPC whenever there is more buffered data than
 * can be copied to userspace, but that's only interesting if we weren't able
 * to copy some data because it implies the userspace buffer is too small to
 * receive a single record (and we never split records).
 *
 * Another case with ret == -EFAULT is more of a grey area since it would seem
 * like bad form for userspace to ask us to overrun its buffer, but the user
 * knows best:
 *
 *   http://yarchive.net/comp/linux/partial_reads_writes.html
 *
 * Returns: The number of bytes copied or a negative error code on failure.
 */
static ssize_t i915_perf_read_locked(struct i915_perf_stream *stream,
				     struct file *file,
				     char __user *buf,
				     size_t count,
				     loff_t *ppos)
{
	/* Note we keep the offset (aka bytes read) separate from any
	 * error status so that the final check for whether we return
	 * the bytes read with a higher precedence than any error (see
	 * comment below) doesn't need to be handled/duplicated in
	 * stream->ops->read() implementations.
	 */
	size_t offset = 0;
	int ret = stream->ops->read(stream, buf, count, &offset);

	return offset ?: (ret ?: -EAGAIN);
}

/**
 * i915_perf_read - handles read() FOP for i915 perf stream FDs
 * @file: An i915 perf stream file
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @ppos: (inout) file seek position (unused)
 *
 * The entry point for handling a read() on a stream file descriptor from
 * userspace. Most of the work is left to the i915_perf_read_locked() and
 * &i915_perf_stream_ops->read but to save having stream implementations (of
 * which we might have multiple later) we handle blocking read here.
 *
 * We can also consistently treat trying to read from a disabled stream
 * as an IO error so implementations can assume the stream is enabled
 * while reading.
 *
 * Returns: The number of bytes copied or a negative error code on failure.
 */
static ssize_t i915_perf_read(struct file *file,
			      char __user *buf,
			      size_t count,
			      loff_t *ppos)
{
	struct i915_perf_stream *stream = file->private_data;
	struct drm_i915_private *dev_priv = stream->dev_priv;
	ssize_t ret;

	/* To ensure it's handled consistently we simply treat all reads of a
	 * disabled stream as an error. In particular it might otherwise lead
	 * to a deadlock for blocking file descriptors...
	 */
	if (!stream->enabled)
		return -EIO;

	if (!(file->f_flags & O_NONBLOCK)) {
		/* There's the small chance of false positives from
		 * stream->ops->wait_unlocked.
		 *
		 * E.g. with single context filtering since we only wait until
		 * oabuffer has >= 1 report we don't immediately know whether
		 * any reports really belong to the current context
		 */
		do {
			ret = stream->ops->wait_unlocked(stream);
			if (ret)
				return ret;

			mutex_lock(&dev_priv->perf.lock);
			ret = i915_perf_read_locked(stream, file,
						    buf, count, ppos);
			mutex_unlock(&dev_priv->perf.lock);
		} while (ret == -EAGAIN);
	} else {
		mutex_lock(&dev_priv->perf.lock);
		ret = i915_perf_read_locked(stream, file, buf, count, ppos);
		mutex_unlock(&dev_priv->perf.lock);
	}

	if (ret >= 0) {
		/* Maybe make ->pollin per-stream state if we support multiple
		 * concurrent streams in the future.
		 */
		dev_priv->perf.oa.pollin = false;
	}

	return ret;
}

static enum hrtimer_restart oa_poll_check_timer_cb(struct hrtimer *hrtimer)
{
	struct drm_i915_private *dev_priv =
		container_of(hrtimer, typeof(*dev_priv),
			     perf.oa.poll_check_timer);

	if (!dev_priv->perf.oa.ops.oa_buffer_is_empty(dev_priv)) {
		dev_priv->perf.oa.pollin = true;
		wake_up(&dev_priv->perf.oa.poll_wq);
	}

	hrtimer_forward_now(hrtimer, ns_to_ktime(POLL_PERIOD));

	return HRTIMER_RESTART;
}

/**
 * i915_perf_poll_locked - poll_wait() with a suitable wait queue for stream
 * @dev_priv: i915 device instance
 * @stream: An i915 perf stream
 * @file: An i915 perf stream file
 * @wait: poll() state table
 *
 * For handling userspace polling on an i915 perf stream, this calls through to
 * &i915_perf_stream_ops->poll_wait to call poll_wait() with a wait queue that
 * will be woken for new stream data.
 *
 * Note: The &drm_i915_private->perf.lock mutex has been taken to serialize
 * with any non-file-operation driver hooks.
 *
 * Returns: any poll events that are ready without sleeping
 */
static unsigned int i915_perf_poll_locked(struct drm_i915_private *dev_priv,
					  struct i915_perf_stream *stream,
					  struct file *file,
					  poll_table *wait)
{
	unsigned int events = 0;

	stream->ops->poll_wait(stream, file, wait);

	/* Note: we don't explicitly check whether there's something to read
	 * here since this path may be very hot depending on what else
	 * userspace is polling, or on the timeout in use. We rely solely on
	 * the hrtimer/oa_poll_check_timer_cb to notify us when there are
	 * samples to read.
	 */
	if (dev_priv->perf.oa.pollin)
		events |= POLLIN;

	return events;
}

/**
 * i915_perf_poll - call poll_wait() with a suitable wait queue for stream
 * @file: An i915 perf stream file
 * @wait: poll() state table
 *
 * For handling userspace polling on an i915 perf stream, this ensures
 * poll_wait() gets called with a wait queue that will be woken for new stream
 * data.
 *
 * Note: Implementation deferred to i915_perf_poll_locked()
 *
 * Returns: any poll events that are ready without sleeping
 */
static unsigned int i915_perf_poll(struct file *file, poll_table *wait)
{
	struct i915_perf_stream *stream = file->private_data;
	struct drm_i915_private *dev_priv = stream->dev_priv;
	int ret;

	mutex_lock(&dev_priv->perf.lock);
	ret = i915_perf_poll_locked(dev_priv, stream, file, wait);
	mutex_unlock(&dev_priv->perf.lock);

	return ret;
}

/**
 * i915_perf_enable_locked - handle `I915_PERF_IOCTL_ENABLE` ioctl
 * @stream: A disabled i915 perf stream
 *
 * [Re]enables the associated capture of data for this stream.
 *
 * If a stream was previously enabled then there's currently no intention
 * to provide userspace any guarantee about the preservation of previously
 * buffered data.
 */
static void i915_perf_enable_locked(struct i915_perf_stream *stream)
{
	if (stream->enabled)
		return;

	/* Allow stream->ops->enable() to refer to this */
	stream->enabled = true;

	if (stream->ops->enable)
		stream->ops->enable(stream);
}

/**
 * i915_perf_disable_locked - handle `I915_PERF_IOCTL_DISABLE` ioctl
 * @stream: An enabled i915 perf stream
 *
 * Disables the associated capture of data for this stream.
 *
 * The intention is that disabling an re-enabling a stream will ideally be
 * cheaper than destroying and re-opening a stream with the same configuration,
 * though there are no formal guarantees about what state or buffered data
 * must be retained between disabling and re-enabling a stream.
 *
 * Note: while a stream is disabled it's considered an error for userspace
 * to attempt to read from the stream (-EIO).
 */
static void i915_perf_disable_locked(struct i915_perf_stream *stream)
{
	if (!stream->enabled)
		return;

	/* Allow stream->ops->disable() to refer to this */
	stream->enabled = false;

	if (stream->ops->disable)
		stream->ops->disable(stream);
}

/**
 * i915_perf_ioctl - support ioctl() usage with i915 perf stream FDs
 * @stream: An i915 perf stream
 * @cmd: the ioctl request
 * @arg: the ioctl data
 *
 * Note: The &drm_i915_private->perf.lock mutex has been taken to serialize
 * with any non-file-operation driver hooks.
 *
 * Returns: zero on success or a negative error code. Returns -EINVAL for
 * an unknown ioctl request.
 */
static long i915_perf_ioctl_locked(struct i915_perf_stream *stream,
				   unsigned int cmd,
				   unsigned long arg)
{
	switch (cmd) {
	case I915_PERF_IOCTL_ENABLE:
		i915_perf_enable_locked(stream);
		return 0;
	case I915_PERF_IOCTL_DISABLE:
		i915_perf_disable_locked(stream);
		return 0;
	}

	return -EINVAL;
}

/**
 * i915_perf_ioctl - support ioctl() usage with i915 perf stream FDs
 * @file: An i915 perf stream file
 * @cmd: the ioctl request
 * @arg: the ioctl data
 *
 * Implementation deferred to i915_perf_ioctl_locked().
 *
 * Returns: zero on success or a negative error code. Returns -EINVAL for
 * an unknown ioctl request.
 */
static long i915_perf_ioctl(struct file *file,
			    unsigned int cmd,
			    unsigned long arg)
{
	struct i915_perf_stream *stream = file->private_data;
	struct drm_i915_private *dev_priv = stream->dev_priv;
	long ret;

	mutex_lock(&dev_priv->perf.lock);
	ret = i915_perf_ioctl_locked(stream, cmd, arg);
	mutex_unlock(&dev_priv->perf.lock);

	return ret;
}

/**
 * i915_perf_destroy_locked - destroy an i915 perf stream
 * @stream: An i915 perf stream
 *
 * Frees all resources associated with the given i915 perf @stream, disabling
 * any associated data capture in the process.
 *
 * Note: The &drm_i915_private->perf.lock mutex has been taken to serialize
 * with any non-file-operation driver hooks.
 */
static void i915_perf_destroy_locked(struct i915_perf_stream *stream)
{
	if (stream->enabled)
		i915_perf_disable_locked(stream);

	if (stream->ops->destroy)
		stream->ops->destroy(stream);

	list_del(&stream->link);

	if (stream->ctx)
		i915_gem_context_put_unlocked(stream->ctx);

	kfree(stream);
}

/**
 * i915_perf_release - handles userspace close() of a stream file
 * @inode: anonymous inode associated with file
 * @file: An i915 perf stream file
 *
 * Cleans up any resources associated with an open i915 perf stream file.
 *
 * NB: close() can't really fail from the userspace point of view.
 *
 * Returns: zero on success or a negative error code.
 */
static int i915_perf_release(struct inode *inode, struct file *file)
{
	struct i915_perf_stream *stream = file->private_data;
	struct drm_i915_private *dev_priv = stream->dev_priv;

	mutex_lock(&dev_priv->perf.lock);
	i915_perf_destroy_locked(stream);
	mutex_unlock(&dev_priv->perf.lock);

	return 0;
}


static const struct file_operations fops = {
	.owner		= THIS_MODULE,
	.llseek		= no_llseek,
	.release	= i915_perf_release,
	.poll		= i915_perf_poll,
	.read		= i915_perf_read,
	.unlocked_ioctl	= i915_perf_ioctl,
};


static struct i915_gem_context *
lookup_context(struct drm_i915_private *dev_priv,
	       struct drm_i915_file_private *file_priv,
	       u32 ctx_user_handle)
{
	struct i915_gem_context *ctx;
	int ret;

	ret = i915_mutex_lock_interruptible(&dev_priv->drm);
	if (ret)
		return ERR_PTR(ret);

	ctx = i915_gem_context_lookup(file_priv, ctx_user_handle);
	if (!IS_ERR(ctx))
		i915_gem_context_get(ctx);

	mutex_unlock(&dev_priv->drm.struct_mutex);

	return ctx;
}

/**
 * i915_perf_open_ioctl_locked - DRM ioctl() for userspace to open a stream FD
 * @dev_priv: i915 device instance
 * @param: The open parameters passed to 'DRM_I915_PERF_OPEN`
 * @props: individually validated u64 property value pairs
 * @file: drm file
 *
 * See i915_perf_ioctl_open() for interface details.
 *
 * Implements further stream config validation and stream initialization on
 * behalf of i915_perf_open_ioctl() with the &drm_i915_private->perf.lock mutex
 * taken to serialize with any non-file-operation driver hooks.
 *
 * Note: at this point the @props have only been validated in isolation and
 * it's still necessary to validate that the combination of properties makes
 * sense.
 *
 * In the case where userspace is interested in OA unit metrics then further
 * config validation and stream initialization details will be handled by
 * i915_oa_stream_init(). The code here should only validate config state that
 * will be relevant to all stream types / backends.
 *
 * Returns: zero on success or a negative error code.
 */
static int
i915_perf_open_ioctl_locked(struct drm_i915_private *dev_priv,
			    struct drm_i915_perf_open_param *param,
			    struct perf_open_properties *props,
			    struct drm_file *file)
{
	struct i915_gem_context *specific_ctx = NULL;
	struct i915_perf_stream *stream = NULL;
	unsigned long f_flags = 0;
	int stream_fd;
	int ret;

	if (props->single_context) {
		u32 ctx_handle = props->ctx_handle;
		struct drm_i915_file_private *file_priv = file->driver_priv;

		specific_ctx = lookup_context(dev_priv, file_priv, ctx_handle);
		if (IS_ERR(specific_ctx)) {
			ret = PTR_ERR(specific_ctx);
			if (ret != -EINTR)
				DRM_DEBUG("Failed to look up context with ID %u for opening perf stream\n",
					  ctx_handle);
			goto err;
		}
	}

	/* Similar to perf's kernel.perf_paranoid_cpu sysctl option
	 * we check a dev.i915.perf_stream_paranoid sysctl option
	 * to determine if it's ok to access system wide OA counters
	 * without CAP_SYS_ADMIN privileges.
	 */
	if (!specific_ctx &&
	    i915_perf_stream_paranoid && !capable(CAP_SYS_ADMIN)) {
		DRM_DEBUG("Insufficient privileges to open system-wide i915 perf stream\n");
		ret = -EACCES;
		goto err_ctx;
	}

	stream = kzalloc(sizeof(*stream), GFP_KERNEL);
	if (!stream) {
		ret = -ENOMEM;
		goto err_ctx;
	}

	stream->dev_priv = dev_priv;
	stream->ctx = specific_ctx;

	ret = i915_oa_stream_init(stream, param, props);
	if (ret)
		goto err_alloc;

	/* we avoid simply assigning stream->sample_flags = props->sample_flags
	 * to have _stream_init check the combination of sample flags more
	 * thoroughly, but still this is the expected result at this point.
	 */
	if (WARN_ON(stream->sample_flags != props->sample_flags)) {
		ret = -ENODEV;
		goto err_flags;
	}

	list_add(&stream->link, &dev_priv->perf.streams);

	if (param->flags & I915_PERF_FLAG_FD_CLOEXEC)
		f_flags |= O_CLOEXEC;
	if (param->flags & I915_PERF_FLAG_FD_NONBLOCK)
		f_flags |= O_NONBLOCK;

	stream_fd = anon_inode_getfd("[i915_perf]", &fops, stream, f_flags);
	if (stream_fd < 0) {
		ret = stream_fd;
		goto err_open;
	}

	if (!(param->flags & I915_PERF_FLAG_DISABLED))
		i915_perf_enable_locked(stream);

	return stream_fd;

err_open:
	list_del(&stream->link);
err_flags:
	if (stream->ops->destroy)
		stream->ops->destroy(stream);
err_alloc:
	kfree(stream);
err_ctx:
	if (specific_ctx)
		i915_gem_context_put_unlocked(specific_ctx);
err:
	return ret;
}

/**
 * read_properties_unlocked - validate + copy userspace stream open properties
 * @dev_priv: i915 device instance
 * @uprops: The array of u64 key value pairs given by userspace
 * @n_props: The number of key value pairs expected in @uprops
 * @props: The stream configuration built up while validating properties
 *
 * Note this function only validates properties in isolation it doesn't
 * validate that the combination of properties makes sense or that all
 * properties necessary for a particular kind of stream have been set.
 *
 * Note that there currently aren't any ordering requirements for properties so
 * we shouldn't validate or assume anything about ordering here. This doesn't
 * rule out defining new properties with ordering requirements in the future.
 */
static int read_properties_unlocked(struct drm_i915_private *dev_priv,
				    u64 __user *uprops,
				    u32 n_props,
				    struct perf_open_properties *props)
{
	u64 __user *uprop = uprops;
	int i;

	memset(props, 0, sizeof(struct perf_open_properties));

	if (!n_props) {
		DRM_DEBUG("No i915 perf properties given\n");
		return -EINVAL;
	}

	/* Considering that ID = 0 is reserved and assuming that we don't
	 * (currently) expect any configurations to ever specify duplicate
	 * values for a particular property ID then the last _PROP_MAX value is
	 * one greater than the maximum number of properties we expect to get
	 * from userspace.
	 */
	if (n_props >= DRM_I915_PERF_PROP_MAX) {
		DRM_DEBUG("More i915 perf properties specified than exist\n");
		return -EINVAL;
	}

	for (i = 0; i < n_props; i++) {
		u64 oa_period, oa_freq_hz;
		u64 id, value;
		int ret;

		ret = get_user(id, uprop);
		if (ret)
			return ret;

		ret = get_user(value, uprop + 1);
		if (ret)
			return ret;

		if (id == 0 || id >= DRM_I915_PERF_PROP_MAX) {
			DRM_DEBUG("Unknown i915 perf property ID\n");
			return -EINVAL;
		}

		switch ((enum drm_i915_perf_property_id)id) {
		case DRM_I915_PERF_PROP_CTX_HANDLE:
			props->single_context = 1;
			props->ctx_handle = value;
			break;
		case DRM_I915_PERF_PROP_SAMPLE_OA:
			props->sample_flags |= SAMPLE_OA_REPORT;
			break;
		case DRM_I915_PERF_PROP_OA_METRICS_SET:
			if (value == 0 ||
			    value > dev_priv->perf.oa.n_builtin_sets) {
				DRM_DEBUG("Unknown OA metric set ID\n");
				return -EINVAL;
			}
			props->metrics_set = value;
			break;
		case DRM_I915_PERF_PROP_OA_FORMAT:
			if (value == 0 || value >= I915_OA_FORMAT_MAX) {
				DRM_DEBUG("Invalid OA report format\n");
				return -EINVAL;
			}
			if (!dev_priv->perf.oa.oa_formats[value].size) {
				DRM_DEBUG("Invalid OA report format\n");
				return -EINVAL;
			}
			props->oa_format = value;
			break;
		case DRM_I915_PERF_PROP_OA_EXPONENT:
			if (value > OA_EXPONENT_MAX) {
				DRM_DEBUG("OA timer exponent too high (> %u)\n",
					 OA_EXPONENT_MAX);
				return -EINVAL;
			}

			/* Theoretically we can program the OA unit to sample
			 * every 160ns but don't allow that by default unless
			 * root.
			 *
			 * On Haswell the period is derived from the exponent
			 * as:
			 *
			 *   period = 80ns * 2^(exponent + 1)
			 */
			BUILD_BUG_ON(sizeof(oa_period) != 8);
			oa_period = 80ull * (2ull << value);

			/* This check is primarily to ensure that oa_period <=
			 * UINT32_MAX (before passing to do_div which only
			 * accepts a u32 denominator), but we can also skip
			 * checking anything < 1Hz which implicitly can't be
			 * limited via an integer oa_max_sample_rate.
			 */
			if (oa_period <= NSEC_PER_SEC) {
				u64 tmp = NSEC_PER_SEC;
				do_div(tmp, oa_period);
				oa_freq_hz = tmp;
			} else
				oa_freq_hz = 0;

			if (oa_freq_hz > i915_oa_max_sample_rate &&
			    !capable(CAP_SYS_ADMIN)) {
				DRM_DEBUG("OA exponent would exceed the max sampling frequency (sysctl dev.i915.oa_max_sample_rate) %uHz without root privileges\n",
					  i915_oa_max_sample_rate);
				return -EACCES;
			}

			props->oa_periodic = true;
			props->oa_period_exponent = value;
			break;
		case DRM_I915_PERF_PROP_MAX:
			MISSING_CASE(id);
			return -EINVAL;
		}

		uprop += 2;
	}

	return 0;
}

/**
 * i915_perf_open_ioctl - DRM ioctl() for userspace to open a stream FD
 * @dev: drm device
 * @data: ioctl data copied from userspace (unvalidated)
 * @file: drm file
 *
 * Validates the stream open parameters given by userspace including flags
 * and an array of u64 key, value pair properties.
 *
 * Very little is assumed up front about the nature of the stream being
 * opened (for instance we don't assume it's for periodic OA unit metrics). An
 * i915-perf stream is expected to be a suitable interface for other forms of
 * buffered data written by the GPU besides periodic OA metrics.
 *
 * Note we copy the properties from userspace outside of the i915 perf
 * mutex to avoid an awkward lockdep with mmap_sem.
 *
 * Most of the implementation details are handled by
 * i915_perf_open_ioctl_locked() after taking the &drm_i915_private->perf.lock
 * mutex for serializing with any non-file-operation driver hooks.
 *
 * Return: A newly opened i915 Perf stream file descriptor or negative
 * error code on failure.
 */
int i915_perf_open_ioctl(struct drm_device *dev, void *data,
			 struct drm_file *file)
{
	struct drm_i915_private *dev_priv = dev->dev_private;
	struct drm_i915_perf_open_param *param = data;
	struct perf_open_properties props;
	u32 known_open_flags;
	int ret;

	if (!dev_priv->perf.initialized) {
		DRM_DEBUG("i915 perf interface not available for this system\n");
		return -ENOTSUPP;
	}

	known_open_flags = I915_PERF_FLAG_FD_CLOEXEC |
			   I915_PERF_FLAG_FD_NONBLOCK |
			   I915_PERF_FLAG_DISABLED;
	if (param->flags & ~known_open_flags) {
		DRM_DEBUG("Unknown drm_i915_perf_open_param flag\n");
		return -EINVAL;
	}

	ret = read_properties_unlocked(dev_priv,
				       u64_to_user_ptr(param->properties_ptr),
				       param->num_properties,
				       &props);
	if (ret)
		return ret;

	mutex_lock(&dev_priv->perf.lock);
	ret = i915_perf_open_ioctl_locked(dev_priv, param, &props, file);
	mutex_unlock(&dev_priv->perf.lock);

	return ret;
}

/**
 * i915_perf_register - exposes i915-perf to userspace
 * @dev_priv: i915 device instance
 *
 * In particular OA metric sets are advertised under a sysfs metrics/
 * directory allowing userspace to enumerate valid IDs that can be
 * used to open an i915-perf stream.
 */
void i915_perf_register(struct drm_i915_private *dev_priv)
{
	if (!IS_HASWELL(dev_priv))
		return;

	if (!dev_priv->perf.initialized)
		return;

	/* To be sure we're synchronized with an attempted
	 * i915_perf_open_ioctl(); considering that we register after
	 * being exposed to userspace.
	 */
	mutex_lock(&dev_priv->perf.lock);

	dev_priv->perf.metrics_kobj =
		kobject_create_and_add("metrics",
				       &dev_priv->drm.primary->kdev->kobj);
	if (!dev_priv->perf.metrics_kobj)
		goto exit;

	if (i915_perf_register_sysfs_hsw(dev_priv)) {
		kobject_put(dev_priv->perf.metrics_kobj);
		dev_priv->perf.metrics_kobj = NULL;
	}

exit:
	mutex_unlock(&dev_priv->perf.lock);
}

/**
 * i915_perf_unregister - hide i915-perf from userspace
 * @dev_priv: i915 device instance
 *
 * i915-perf state cleanup is split up into an 'unregister' and
 * 'deinit' phase where the interface is first hidden from
 * userspace by i915_perf_unregister() before cleaning up
 * remaining state in i915_perf_fini().
 */
void i915_perf_unregister(struct drm_i915_private *dev_priv)
{
	if (!IS_HASWELL(dev_priv))
		return;

	if (!dev_priv->perf.metrics_kobj)
		return;

	i915_perf_unregister_sysfs_hsw(dev_priv);

	kobject_put(dev_priv->perf.metrics_kobj);
	dev_priv->perf.metrics_kobj = NULL;
}

static struct ctl_table oa_table[] = {
	{
	 .procname = "perf_stream_paranoid",
	 .data = &i915_perf_stream_paranoid,
	 .maxlen = sizeof(i915_perf_stream_paranoid),
	 .mode = 0644,
	 .proc_handler = proc_dointvec_minmax,
	 .extra1 = &zero,
	 .extra2 = &one,
	 },
	{
	 .procname = "oa_max_sample_rate",
	 .data = &i915_oa_max_sample_rate,
	 .maxlen = sizeof(i915_oa_max_sample_rate),
	 .mode = 0644,
	 .proc_handler = proc_dointvec_minmax,
	 .extra1 = &zero,
	 .extra2 = &oa_sample_rate_hard_limit,
	 },
	{}
};

static struct ctl_table i915_root[] = {
	{
	 .procname = "i915",
	 .maxlen = 0,
	 .mode = 0555,
	 .child = oa_table,
	 },
	{}
};

static struct ctl_table dev_root[] = {
	{
	 .procname = "dev",
	 .maxlen = 0,
	 .mode = 0555,
	 .child = i915_root,
	 },
	{}
};

/**
 * i915_perf_init - initialize i915-perf state on module load
 * @dev_priv: i915 device instance
 *
 * Initializes i915-perf state without exposing anything to userspace.
 *
 * Note: i915-perf initialization is split into an 'init' and 'register'
 * phase with the i915_perf_register() exposing state to userspace.
 */
void i915_perf_init(struct drm_i915_private *dev_priv)
{
	if (!IS_HASWELL(dev_priv))
		return;

	hrtimer_init(&dev_priv->perf.oa.poll_check_timer,
		     CLOCK_MONOTONIC, HRTIMER_MODE_REL);
	dev_priv->perf.oa.poll_check_timer.function = oa_poll_check_timer_cb;
	init_waitqueue_head(&dev_priv->perf.oa.poll_wq);

	INIT_LIST_HEAD(&dev_priv->perf.streams);
	mutex_init(&dev_priv->perf.lock);
	spin_lock_init(&dev_priv->perf.hook_lock);

	dev_priv->perf.oa.ops.init_oa_buffer = gen7_init_oa_buffer;
	dev_priv->perf.oa.ops.enable_metric_set = hsw_enable_metric_set;
	dev_priv->perf.oa.ops.disable_metric_set = hsw_disable_metric_set;
	dev_priv->perf.oa.ops.oa_enable = gen7_oa_enable;
	dev_priv->perf.oa.ops.oa_disable = gen7_oa_disable;
	dev_priv->perf.oa.ops.read = gen7_oa_read;
	dev_priv->perf.oa.ops.oa_buffer_is_empty =
		gen7_oa_buffer_is_empty_fop_unlocked;

	dev_priv->perf.oa.timestamp_frequency = 12500000;

	dev_priv->perf.oa.oa_formats = hsw_oa_formats;

	dev_priv->perf.oa.n_builtin_sets =
		i915_oa_n_builtin_metric_sets_hsw;

	dev_priv->perf.sysctl_header = register_sysctl_table(dev_root);

	dev_priv->perf.initialized = true;
}

/**
 * i915_perf_fini - Counter part to i915_perf_init()
 * @dev_priv: i915 device instance
 */
void i915_perf_fini(struct drm_i915_private *dev_priv)
{
	if (!dev_priv->perf.initialized)
		return;

	unregister_sysctl_table(dev_priv->perf.sysctl_header);

	memset(&dev_priv->perf.oa.ops, 0, sizeof(dev_priv->perf.oa.ops));
	dev_priv->perf.initialized = false;
}