GPU saves accumulated context runtime (in CS timestamp units) in PPHWSP
which will be useful for us in cases when we are not able to track context
busyness ourselves (like with GuC). Keep a copy of this in struct
intel_context from where it can be easily read even if the context is not
pinned.
v2:
(Chris)
* Do not store pphwsp address in intel_context.
* Log CS wrap-around.
* Simplify calculation by relying on integer wraparound.
v3:
* Include total/avg in traces and error state for debugging
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200216133620.394962-1-chris@chris-wilson.co.uk
Currently when we load the driver we set distrust_bios_wm=true, which
will cause active_pipe_changes to get flagged even when we're not
toggling any pipes on/off. The reason being that we want to fully
redistribute the dbuf among the active pipes and ignore whatever
state the firmware left behind.
Unfortunately when the code flags active_pipe_changes it doesn't
set state->modeset to true, which means the hardware dbuf state
won't actually get updated. Hence the hardware and software
states go out of sync, which can result in planes trying to use a
disabled dbuf slice. Suprisingly that only seems to corrupt the
display rather than making the whole display engine keel over.
Let's fix this for now by flagging state->modeset whenever
distrust_bios_wm is set.
Eventually we'll likely want to rip out all of this mess and
introduce proper statye tracking for dbuf. But that requires
more work. Toss in a FIXME to that effect.
Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Fixes: ff2cd8635e ("drm/i915: Correctly map DBUF slices to pipes")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200213140412.32697-4-stanislav.lisovskiy@intel.com
We lack full state readout of DSC config, which may lead to DSC enable
using a config that's all zeros, failing spectacularly. Force full
modeset and thus compute config at probe to get a sane state, until we
implement DSC state readout. Any fastset that did appear to work with
DSC at probe, worked by coincidence. [1] is an example of a change that
triggered the issue on TGL DSI DSC.
[1] http://patchwork.freedesktop.org/patch/msgid/20200212150102.7600-1-ville.syrjala@linux.intel.com
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: stable@vger.kernel.org
Fixes: fbacb15ea8 ("drm/i915/dsc: add basic hardware state readout support")
Acked-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200213140412.32697-3-stanislav.lisovskiy@intel.com
TGL BIOS seems to enable both DBuf slices ocasionally, depending
how many displays are connected, while i915 according to BSpec
was powering on S1 DBuf slice, until a modeset was done.
This was causing a brief flash during the boot as we were
disabling slice, previously used by BIOS with that.
To prevent this, now we are ensuring tht we are enabling
_at least_ one slice, but if there are more, let's not
power them off.
Fixes: ff2cd8635e ("drm/i915: Correctly map DBUF slices to pipes")
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200213140412.32697-2-stanislav.lisovskiy@intel.com
Commit 1c9d2eb241 ("drm/i915: move intel_dp_set_m_n() to encoder for
DDI platforms") moved the intel_dp_set_m_n() from hsw_crtc_enable()
to intel_ddi_pre_enable_dp() but it missed add it to
intel_mst_pre_enable_dp() causing MST slaves to not work.
v2: Not setting intel_ddi_set_dp_msa() twice for MST master
Fixes: 1c9d2eb241 ("drm/i915: move intel_dp_set_m_n() to encoder for DDI platforms")
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200211185008.30806-1-jose.souza@intel.com
Sometimes the error interrupt can fire even before we have seen the
request go active -- in which case, we end up waiting until the timeout
as the request is already completed. Double check for this case!
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200214120659.3888735-1-chris@chris-wilson.co.uk
The i915_debugfs.c has grown more than a little unwieldy. Split out the
display related debugfs code to a file of its own under display/,
initialized with a separate call. No functional changes.
v2:
- Also moved i915_frontbuffer_tracking, i915_gem_framebuffer,
i915_power_domain_info, i915_dmc_info, i915_ipc_status (Ville)
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200211161451.6867-2-jani.nikula@intel.com
The DMC firmware is about display. Move the handling under display. No
functional changes.
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200211161451.6867-1-jani.nikula@intel.com
Move vga switcheroo and dsm handler register later in
i915_driver_register(), and unregister in i915_driver_unregister(). The
dsm handler unregister is a nop, and is only added for completeness.
My unsubstantiated suspicion is that the vga switcheroo state change
would not work as early as we register the hooks currently. In any case
exposing the interfaces to the world only after we've got everything set
up seems prudent.
Also replace the error handling in vga switcheroo register with a simple
error message. This is done at the same time due to lack of error
propagation from i915_driver_register().
Cc: Lukas Wunner <lukas@wunner.de>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200211162802.16180-1-jani.nikula@intel.com
drm->dev_private is to be avoided. Use to_i915() on the struct
drm_device pointer instead. Rename the affected local dev_priv variables
to i915 while at it.
Cc: Wambui Karuga <wambui.karugax@gmail.com>
Reviewed-by: Wambui Karuga <wambui.karugax@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200211134427.31605-1-jani.nikula@intel.com
Originally, I did not expect having to rewind a context upon
timeslicing: the point was to replace the executing context with a
non-executing one! However, given a second context that depends on
requests from the first, we may have to split the requests along the
first context to execute the second, causing us to partially replay the
first context and so have to rewind its RING_TAIL.
References: 5ba32c7be8 ("drm/i915/execlists: Always force a context reload when rewinding RING_TAIL")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200213140150.3639027-1-chris@chris-wilson.co.uk
With debugging turned off, we have to tell the compiler not to warn
about the unused debug locals.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200213081217.3107410-1-chris@chris-wilson.co.uk
This is in mcr range of register, thus we can only verify
it through mmio. Use engine wa list with mcr range verification
skip.
Fixes: 0db1a5f870 ("drm/i915: Implement Wa_1607090982")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200212165707.11143-1-mika.kuoppala@linux.intel.com
Apply vast quantities of poison and not tell anyone to see if we fall
for the trap of using a stale RING_HEAD.
References: 42827350f7 ("drm/i915/gt: Avoid resetting ring->head outside of its timeline mutex")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Andi Shyti <andi.shyti@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200211205615.1190127-2-chris@chris-wilson.co.uk
On retiring the request, we should not re-use these elements in the ring
(at least not until we fill the ringbuffer and knowingly reuse the space).
Leave behind some poison to (hopefully) trap ourselves if we make a
mistake.
Suggested-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200211205615.1190127-1-chris@chris-wilson.co.uk
If we have a set of active engines marked as being non-persistent, we
lose track of those if the user replaces those engines with
I915_CONTEXT_PARAM_ENGINES. As part of our uABI contract is that
non-persistent requests are terminated if they are no longer being
tracked by the user's context (in order to prevent a lost request
causing an untracked and so unstoppable GPU hang), we need to apply the
same context cancellation upon changing engines.
v2: Track stale engines[] so we only reap at context closure.
v3: Tvrtko spotted races with closing contexts and set-engines, so add a
veneer of kill-everything paranoia to clean up after losing a race.
Fixes: a0e047156c ("drm/i915/gem: Make context persistence optional")
Testcase: igt/gem_ctx_peristence/replace
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200211144831.1011498-1-chris@chris-wilson.co.uk
s/before/after/ again after accidentally changing it the
other way in commit 5604e9ceae ("drm/i915: Simplify
intel_set_cdclk_{pre,post}_plane_update() calling convention")
Cc: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200204154803.25403-1-ville.syrjala@linux.intel.com
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Accidentally removed the 'ret=0' initialization, and thus
we're potentially looking at some stack garbage here.
The whole 'ret = do_stuff; if (!ret) do_other_stuff;' pattern
confuses my brain so let's replace it with the standard
immediate return thing.
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Fixes: 28a30b45f5 ("drm/i915: Convert cdclk to global state")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200207152228.1054-1-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Currently on execlists, we use a local hwsp for the kernel_context,
rather than the engine's HWSP, as this is the default for execlists.
However, seqno wrap requires allocating a new HWSP cacheline, and may
require pinning a new HWSP page in the GGTT. This operation requiring
pinning in the GGTT is not allowed within the kernel_context timeline,
as doing so may require re-entering the kernel_context in order to evict
from the GGTT. As we want to avoid requiring a new HWSP for the
kernel_context, we can use the permanently pinned engine's HWSP instead.
However to do so we must prevent the use of semaphores reading the
kernel_context's HWSP, as the use of semaphores do not support rollover
onto the same cacheline. Fortunately, the kernel_context is mostly
isolated, so unlikely to give benefit to semaphores.
Reported-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200210205722.794180-5-chris@chris-wilson.co.uk
We can not require that the system process a tasklet in reasonable time
(thanks be to ksoftirqd), but we can insist that having waited
sufficiently for the error interrupt to have been raised and having
kicked the tasklet, the reset has begun and the request will be marked
as in error (if not already completed).
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200210205722.794180-3-chris@chris-wilson.co.uk
Converts various instances of the printk based drm logging macros to the
struct drm_device based logging macros in
i915/display/intel_dp_link_training.c.
This also involves extracting the drm_i915_private device pointer from
the intel_dp type to use in the various macros.
Signed-off-by: Wambui Karuga <wambui.karugax@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200206080014.13759-3-wambui.karugax@gmail.com
We manipulate ring->head while active in i915_request_retire underneath
the timeline manipulation. We cannot rely on a stable ring->head outside
of the timeline->mutex, in particular while setting up the context for
resume and reset.
Closes: https://gitlab.freedesktop.org/drm/intel/issues/1126
Fixes: 0881954965 ("drm/i915: Introduce intel_context.pin_mutex for pin management")
Fixes: e5dadff4b0 ("drm/i915: Protect request retirement with timeline->mutex")
References: f3c0efc9fe ("drm/i915/execlists: Leave resetting ring to intel_ring")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200211120131.958949-1-chris@chris-wilson.co.uk
As Gen12 onwards there are HDCP instances for each transcoder
instead of port, remove the (port < PORT_E) hdcp support
limitation for platform >= Gen12.
v2:
- Nuke the comment and cosmetic changes. [Jani]
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200207144116.20172-1-anshuman.gupta@intel.com
dma-bufs are device coherent, with explicit CPU synchronisation provided
via the begin/end cpu access ioctls. As the coherency of the dma-buf is
explicitly defined to be under user control, flushing any caches on
attach/detach of the dma-buf is additional work that doesn't aide the
user in the slightest.
Suggested-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Dongwon Kim <dongwon.kim@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171130180702.29357-1-chris@chris-wilson.co.uk
Reduce the amount of work we do to verify client blt correctness as
currently our 0.5s subtests takes about 15s on slower devices!
v2: Grow the maximum block size until we run out of time
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200210231047.810929-1-chris@chris-wilson.co.uk
A recent bspec update added an extra voltage level that we didn't have
on ICL and new criteria for selecting the level.
Bspec: 49208
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200207001417.1229251-2-matthew.d.roper@intel.com
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Voltage level depends not only on the cdclk, but also on the DDI clock.
Last time the bspec voltage level table for EHL was updated, we only
updated the cdclk requirements, but forgot to account for the new port
clock criteria.
Bspec: 21809
Fixes: d147483884 ("drm/i915/ehl: Update voltage level checks")
Cc: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200207001417.1229251-1-matthew.d.roper@intel.com
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Add a basic description about how DC3CO works to help people not
familiar with it.
While at it, I also improved the delayed work handle and function
names and removed a debug message that is ambiguous and not much
useful, no changes in behavior here.
Cc: Anshuman Gupta <anshuman.gupta@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200205214945.131012-1-jose.souza@intel.com
live_preempt_hang's use of hang injection has been superseded by
live_preempt_reset's use of an non-preemptible spinner. The latter does
not require intrusive hacks into the code.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200209230838.361154-2-chris@chris-wilson.co.uk
Commit 21fd23ac22 ("drm/i915: move pipe, pch and vblank enable to
encoders on DDI platforms") pushed pipe and vblank enable to encoders on
DDI platforms, however it missed the DP MST encoder. Fix it.
Fixes: 21fd23ac22 ("drm/i915: move pipe, pch and vblank enable to encoders on DDI platforms")
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Reported-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Reviewed-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Tested-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200205082959.31317-1-jani.nikula@intel.com
Recording the frequent inspection of CSB head/tail when there is
expected to be no update adds noise to the debug trace. (Not entirely
useless, but since we know the sequence of function calls, we can
surmise the function was called -- so redundant.)
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200209131922.180287-2-chris@chris-wilson.co.uk
In eliminating the recursion from walking the tree of signalers/waiters
for processing the hold/unhold operations, a crucial error crept in
where we looked at the parent request and not the list element when
processing the list.
Brown paper bag, much?
Closes: https://gitlab.freedesktop.org/drm/intel/issues/1166
Fixes: 32ff621fd7 ("drm/i915/gt: Allow temporary suspension of inflight requests")
Fixes: 748317386a ("drm/i915/execlists: Offline error capture")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200209131922.180287-1-chris@chris-wilson.co.uk
We have switched from tail manipulation to forced context restore
to implement WaIdleLiteRestore. Remove the old defines and comments.
Note: we still do emit the WA tail, and use it as our first attempt to
avoid forcing a full-restore instead of a lite-restore, we just have a
much stronger backup mechanism for repeated preemptions.
References: f26a9e959a ("drm/i915/gt: Detect if we miss WaIdleLiteRestore")
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200203163312.15475-1-mika.kuoppala@linux.intel.com
Commit 4f2a572eda ("drm/i915/userptr: Never allow userptr into the
mappable GGTT") made I915_GEM_MMAP_GTT IOCTLs to fail when attempted
on a userptr object in order to protect from a lockdep splat. Later
on, new mapping types were introduced by commit cc662126b4
("drm/i915: Introduce DRM_I915_GEM_MMAP_OFFSET"). Those new mapping
types suffer from the same lockdep splat issue but they now succeed
when tried on top of a userptr object. Fix it.
v2: Don't play with the -ENODEV driver response (Chris)
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Cc: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200204162302.1299516-1-chris@chris-wilson.co.uk
