drm: Begin an API for in-kernel clients

This the beginning of an API for in-kernel clients.
First out is a way to get a framebuffer backed by a dumb buffer.

Only GEM drivers are supported.
The original idea of using an exported dma-buf was dropped because it
also creates an anonomous file descriptor which doesn't work when the
buffer is created from a kernel thread. The easy way out is to use
drm_driver.gem_prime_vmap to get the virtual address, which requires a
GEM object. This excludes the vmwgfx driver which is the only non-GEM
driver apart from the legacy ones. A solution for vmwgfx will have to be
worked out later if it wants to support the client API which it probably
will when we have a bootsplash client.

Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180703160354.59955-2-noralf@tronnes.org

Documentation/gpu/drm-client.rst

@@ -0,0 +1,12 @@
+=================
+Kernel clients
+=================
+
+.. kernel-doc:: drivers/gpu/drm/drm_client.c
+   :doc: overview
+
+.. kernel-doc:: include/drm/drm_client.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_client.c
+   :export:

Documentation/gpu/index.rst

@@ -10,6 +10,7 @@ Linux GPU Driver Developer's Guide
    drm-kms
    drm-kms-helpers
    drm-uapi
+   drm-client
    drivers
    vga-switcheroo
    vgaarbiter

drivers/gpu/drm/Makefile

@@ -18,7 +18,7 @@ drm-y       :=	drm_auth.o drm_bufs.o drm_cache.o \
 		drm_encoder.o drm_mode_object.o drm_property.o \
 		drm_plane.o drm_color_mgmt.o drm_print.o \
 		drm_dumb_buffers.o drm_mode_config.o drm_vblank.o \
-		drm_syncobj.o drm_lease.o drm_writeback.o
+		drm_syncobj.o drm_lease.o drm_writeback.o drm_client.o
 
 drm-$(CONFIG_DRM_LIB_RANDOM) += lib/drm_random.o
 drm-$(CONFIG_DRM_VM) += drm_vm.o

drivers/gpu/drm/drm_client.c

@@ -0,0 +1,387 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2018 Noralf Trønnes
+ */
+
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+
+#include <drm/drm_client.h>
+#include <drm/drm_debugfs.h>
+#include <drm/drm_device.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_file.h>
+#include <drm/drm_fourcc.h>
+#include <drm/drm_gem.h>
+#include <drm/drm_mode.h>
+#include <drm/drm_print.h>
+#include <drm/drmP.h>
+
+#include "drm_crtc_internal.h"
+#include "drm_internal.h"
+
+/**
+ * DOC: overview
+ *
+ * This library provides support for clients running in the kernel like fbdev and bootsplash.
+ * Currently it's only partially implemented, just enough to support fbdev.
+ *
+ * GEM drivers which provide a GEM based dumb buffer with a virtual address are supported.
+ */
+
+static int drm_client_open(struct drm_client_dev *client)
+{
+	struct drm_device *dev = client->dev;
+	struct drm_file *file;
+
+	file = drm_file_alloc(dev->primary);
+	if (IS_ERR(file))
+		return PTR_ERR(file);
+
+	mutex_lock(&dev->filelist_mutex);
+	list_add(&file->lhead, &dev->filelist_internal);
+	mutex_unlock(&dev->filelist_mutex);
+
+	client->file = file;
+
+	return 0;
+}
+
+static void drm_client_close(struct drm_client_dev *client)
+{
+	struct drm_device *dev = client->dev;
+
+	mutex_lock(&dev->filelist_mutex);
+	list_del(&client->file->lhead);
+	mutex_unlock(&dev->filelist_mutex);
+
+	drm_file_free(client->file);
+}
+EXPORT_SYMBOL(drm_client_close);
+
+/**
+ * drm_client_new - Create a DRM client
+ * @dev: DRM device
+ * @client: DRM client
+ * @name: Client name
+ * @funcs: DRM client functions (optional)
+ *
+ * The caller needs to hold a reference on @dev before calling this function.
+ * The client is freed when the &drm_device is unregistered. See drm_client_release().
+ *
+ * Returns:
+ * Zero on success or negative error code on failure.
+ */
+int drm_client_new(struct drm_device *dev, struct drm_client_dev *client,
+		   const char *name, const struct drm_client_funcs *funcs)
+{
+	bool registered;
+	int ret;
+
+	if (!drm_core_check_feature(dev, DRIVER_MODESET) ||
+	    !dev->driver->dumb_create || !dev->driver->gem_prime_vmap)
+		return -ENOTSUPP;
+
+	if (funcs && !try_module_get(funcs->owner))
+		return -ENODEV;
+
+	client->dev = dev;
+	client->name = name;
+	client->funcs = funcs;
+
+	ret = drm_client_open(client);
+	if (ret)
+		goto err_put_module;
+
+	mutex_lock(&dev->clientlist_mutex);
+	registered = dev->registered;
+	if (registered)
+		list_add(&client->list, &dev->clientlist);
+	mutex_unlock(&dev->clientlist_mutex);
+	if (!registered) {
+		ret = -ENODEV;
+		goto err_close;
+	}
+
+	drm_dev_get(dev);
+
+	return 0;
+
+err_close:
+	drm_client_close(client);
+err_put_module:
+	if (funcs)
+		module_put(funcs->owner);
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_client_new);
+
+/**
+ * drm_client_release - Release DRM client resources
+ * @client: DRM client
+ *
+ * Releases resources by closing the &drm_file that was opened by drm_client_new().
+ * It is called automatically if the &drm_client_funcs.unregister callback is _not_ set.
+ *
+ * This function should only be called from the unregister callback. An exception
+ * is fbdev which cannot free the buffer if userspace has open file descriptors.
+ *
+ * Note:
+ * Clients cannot initiate a release by themselves. This is done to keep the code simple.
+ * The driver has to be unloaded before the client can be unloaded.
+ */
+void drm_client_release(struct drm_client_dev *client)
+{
+	struct drm_device *dev = client->dev;
+
+	DRM_DEV_DEBUG_KMS(dev->dev, "%s\n", client->name);
+
+	drm_client_close(client);
+	drm_dev_put(dev);
+	if (client->funcs)
+		module_put(client->funcs->owner);
+}
+EXPORT_SYMBOL(drm_client_release);
+
+void drm_client_dev_unregister(struct drm_device *dev)
+{
+	struct drm_client_dev *client, *tmp;
+
+	if (!drm_core_check_feature(dev, DRIVER_MODESET))
+		return;
+
+	mutex_lock(&dev->clientlist_mutex);
+	list_for_each_entry_safe(client, tmp, &dev->clientlist, list) {
+		list_del(&client->list);
+		if (client->funcs && client->funcs->unregister) {
+			client->funcs->unregister(client);
+		} else {
+			drm_client_release(client);
+			kfree(client);
+		}
+	}
+	mutex_unlock(&dev->clientlist_mutex);
+}
+
+/**
+ * drm_client_dev_hotplug - Send hotplug event to clients
+ * @dev: DRM device
+ *
+ * This function calls the &drm_client_funcs.hotplug callback on the attached clients.
+ *
+ * drm_kms_helper_hotplug_event() calls this function, so drivers that use it
+ * don't need to call this function themselves.
+ */
+void drm_client_dev_hotplug(struct drm_device *dev)
+{
+	struct drm_client_dev *client;
+	int ret;
+
+	if (!drm_core_check_feature(dev, DRIVER_MODESET))
+		return;
+
+	mutex_lock(&dev->clientlist_mutex);
+	list_for_each_entry(client, &dev->clientlist, list) {
+		if (!client->funcs || !client->funcs->hotplug)
+			continue;
+
+		ret = client->funcs->hotplug(client);
+		DRM_DEV_DEBUG_KMS(dev->dev, "%s: ret=%d\n", client->name, ret);
+	}
+	mutex_unlock(&dev->clientlist_mutex);
+}
+EXPORT_SYMBOL(drm_client_dev_hotplug);
+
+void drm_client_dev_restore(struct drm_device *dev)
+{
+	struct drm_client_dev *client;
+	int ret;
+
+	if (!drm_core_check_feature(dev, DRIVER_MODESET))
+		return;
+
+	mutex_lock(&dev->clientlist_mutex);
+	list_for_each_entry(client, &dev->clientlist, list) {
+		if (!client->funcs || !client->funcs->restore)
+			continue;
+
+		ret = client->funcs->restore(client);
+		DRM_DEV_DEBUG_KMS(dev->dev, "%s: ret=%d\n", client->name, ret);
+		if (!ret) /* The first one to return zero gets the privilege to restore */
+			break;
+	}
+	mutex_unlock(&dev->clientlist_mutex);
+}
+
+static void drm_client_buffer_delete(struct drm_client_buffer *buffer)
+{
+	struct drm_device *dev = buffer->client->dev;
+
+	if (buffer->vaddr && dev->driver->gem_prime_vunmap)
+		dev->driver->gem_prime_vunmap(buffer->gem, buffer->vaddr);
+
+	if (buffer->gem)
+		drm_gem_object_put_unlocked(buffer->gem);
+
+	drm_mode_destroy_dumb(dev, buffer->handle, buffer->client->file);
+	kfree(buffer);
+}
+
+static struct drm_client_buffer *
+drm_client_buffer_create(struct drm_client_dev *client, u32 width, u32 height, u32 format)
+{
+	struct drm_mode_create_dumb dumb_args = { };
+	struct drm_device *dev = client->dev;
+	struct drm_client_buffer *buffer;
+	struct drm_gem_object *obj;
+	void *vaddr;
+	int ret;
+
+	buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
+	if (!buffer)
+		return ERR_PTR(-ENOMEM);
+
+	buffer->client = client;
+
+	dumb_args.width = width;
+	dumb_args.height = height;
+	dumb_args.bpp = drm_format_plane_cpp(format, 0) * 8;
+	ret = drm_mode_create_dumb(dev, &dumb_args, client->file);
+	if (ret)
+		goto err_free;
+
+	buffer->handle = dumb_args.handle;
+	buffer->pitch = dumb_args.pitch;
+
+	obj = drm_gem_object_lookup(client->file, dumb_args.handle);
+	if (!obj)  {
+		ret = -ENOENT;
+		goto err_delete;
+	}
+
+	buffer->gem = obj;
+
+	/*
+	 * FIXME: The dependency on GEM here isn't required, we could
+	 * convert the driver handle to a dma-buf instead and use the
+	 * backend-agnostic dma-buf vmap support instead. This would
+	 * require that the handle2fd prime ioctl is reworked to pull the
+	 * fd_install step out of the driver backend hooks, to make that
+	 * final step optional for internal users.
+	 */
+	vaddr = dev->driver->gem_prime_vmap(obj);
+	if (!vaddr) {
+		ret = -ENOMEM;
+		goto err_delete;
+	}
+
+	buffer->vaddr = vaddr;
+
+	return buffer;
+
+err_delete:
+	drm_client_buffer_delete(buffer);
+err_free:
+	kfree(buffer);
+
+	return ERR_PTR(ret);
+}
+
+static void drm_client_buffer_rmfb(struct drm_client_buffer *buffer)
+{
+	int ret;
+
+	if (!buffer->fb)
+		return;
+
+	ret = drm_mode_rmfb(buffer->client->dev, buffer->fb->base.id, buffer->client->file);
+	if (ret)
+		DRM_DEV_ERROR(buffer->client->dev->dev,
+			      "Error removing FB:%u (%d)\n", buffer->fb->base.id, ret);
+
+	buffer->fb = NULL;
+}
+
+static int drm_client_buffer_addfb(struct drm_client_buffer *buffer,
+				   u32 width, u32 height, u32 format)
+{
+	struct drm_client_dev *client = buffer->client;
+	struct drm_mode_fb_cmd fb_req = { };
+	const struct drm_format_info *info;
+	int ret;
+
+	info = drm_format_info(format);
+	fb_req.bpp = info->cpp[0] * 8;
+	fb_req.depth = info->depth;
+	fb_req.width = width;
+	fb_req.height = height;
+	fb_req.handle = buffer->handle;
+	fb_req.pitch = buffer->pitch;
+
+	ret = drm_mode_addfb(client->dev, &fb_req, client->file);
+	if (ret)
+		return ret;
+
+	buffer->fb = drm_framebuffer_lookup(client->dev, buffer->client->file, fb_req.fb_id);
+	if (WARN_ON(!buffer->fb))
+		return -ENOENT;
+
+	/* drop the reference we picked up in framebuffer lookup */
+	drm_framebuffer_put(buffer->fb);
+
+	strscpy(buffer->fb->comm, client->name, TASK_COMM_LEN);
+
+	return 0;
+}
+
+/**
+ * drm_client_framebuffer_create - Create a client framebuffer
+ * @client: DRM client
+ * @width: Framebuffer width
+ * @height: Framebuffer height
+ * @format: Buffer format
+ *
+ * This function creates a &drm_client_buffer which consists of a
+ * &drm_framebuffer backed by a dumb buffer.
+ * Call drm_client_framebuffer_delete() to free the buffer.
+ *
+ * Returns:
+ * Pointer to a client buffer or an error pointer on failure.
+ */
+struct drm_client_buffer *
+drm_client_framebuffer_create(struct drm_client_dev *client, u32 width, u32 height, u32 format)
+{
+	struct drm_client_buffer *buffer;
+	int ret;
+
+	buffer = drm_client_buffer_create(client, width, height, format);
+	if (IS_ERR(buffer))
+		return buffer;
+
+	ret = drm_client_buffer_addfb(buffer, width, height, format);
+	if (ret) {
+		drm_client_buffer_delete(buffer);
+		return ERR_PTR(ret);
+	}
+
+	return buffer;
+}
+EXPORT_SYMBOL(drm_client_framebuffer_create);
+
+/**
+ * drm_client_framebuffer_delete - Delete a client framebuffer
+ * @buffer: DRM client buffer (can be NULL)
+ */
+void drm_client_framebuffer_delete(struct drm_client_buffer *buffer)
+{
+	if (!buffer)
+		return;
+
+	drm_client_buffer_rmfb(buffer);
+	drm_client_buffer_delete(buffer);
+}
+EXPORT_SYMBOL(drm_client_framebuffer_delete);

drivers/gpu/drm/drm_drv.c

@@ -34,6 +34,7 @@
 #include <linux/slab.h>
 #include <linux/srcu.h>
 
+#include <drm/drm_client.h>
 #include <drm/drm_drv.h>
 #include <drm/drmP.h>
 
@@ -505,6 +506,8 @@ int drm_dev_init(struct drm_device *dev,
 	dev->driver = driver;
 
 	INIT_LIST_HEAD(&dev->filelist);
+	INIT_LIST_HEAD(&dev->filelist_internal);
+	INIT_LIST_HEAD(&dev->clientlist);
 	INIT_LIST_HEAD(&dev->ctxlist);
 	INIT_LIST_HEAD(&dev->vmalist);
 	INIT_LIST_HEAD(&dev->maplist);
@@ -514,6 +517,7 @@ int drm_dev_init(struct drm_device *dev,
 	spin_lock_init(&dev->event_lock);
 	mutex_init(&dev->struct_mutex);
 	mutex_init(&dev->filelist_mutex);
+	mutex_init(&dev->clientlist_mutex);
 	mutex_init(&dev->ctxlist_mutex);
 	mutex_init(&dev->master_mutex);
 
@@ -569,6 +573,7 @@ int drm_dev_init(struct drm_device *dev,
 err_free:
 	mutex_destroy(&dev->master_mutex);
 	mutex_destroy(&dev->ctxlist_mutex);
+	mutex_destroy(&dev->clientlist_mutex);
 	mutex_destroy(&dev->filelist_mutex);
 	mutex_destroy(&dev->struct_mutex);
 	return ret;
@@ -603,6 +608,7 @@ void drm_dev_fini(struct drm_device *dev)
 
 	mutex_destroy(&dev->master_mutex);
 	mutex_destroy(&dev->ctxlist_mutex);
+	mutex_destroy(&dev->clientlist_mutex);
 	mutex_destroy(&dev->filelist_mutex);
 	mutex_destroy(&dev->struct_mutex);
 	kfree(dev->unique);
@@ -858,6 +864,8 @@ void drm_dev_unregister(struct drm_device *dev)
 
 	dev->registered = false;
 
+	drm_client_dev_unregister(dev);
+
 	if (drm_core_check_feature(dev, DRIVER_MODESET))
 		drm_modeset_unregister_all(dev);
 

drivers/gpu/drm/drm_file.c

@@ -35,6 +35,7 @@
 #include <linux/slab.h>
 #include <linux/module.h>
 
+#include <drm/drm_client.h>
 #include <drm/drm_file.h>
 #include <drm/drmP.h>
 
@@ -444,6 +445,8 @@ void drm_lastclose(struct drm_device * dev)
 
 	if (drm_core_check_feature(dev, DRIVER_LEGACY))
 		drm_legacy_dev_reinit(dev);
+
+	drm_client_dev_restore(dev);
 }
 
 /**

drivers/gpu/drm/drm_probe_helper.c

@@ -33,6 +33,7 @@
 #include <linux/moduleparam.h>
 
 #include <drm/drmP.h>
+#include <drm/drm_client.h>
 #include <drm/drm_crtc.h>
 #include <drm/drm_fourcc.h>
 #include <drm/drm_crtc_helper.h>
@@ -559,6 +560,8 @@ void drm_kms_helper_hotplug_event(struct drm_device *dev)
 	drm_sysfs_hotplug_event(dev);
 	if (dev->mode_config.funcs->output_poll_changed)
 		dev->mode_config.funcs->output_poll_changed(dev);
+
+	drm_client_dev_hotplug(dev);
 }
 EXPORT_SYMBOL(drm_kms_helper_hotplug_event);
 

include/drm/drm_client.h

@@ -0,0 +1,136 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _DRM_CLIENT_H_
+#define _DRM_CLIENT_H_
+
+#include <linux/types.h>
+
+struct drm_client_dev;
+struct drm_device;
+struct drm_file;
+struct drm_framebuffer;
+struct drm_gem_object;
+struct module;
+
+/**
+ * struct drm_client_funcs - DRM client callbacks
+ */
+struct drm_client_funcs {
+	/**
+	 * @owner: The module owner
+	 */
+	struct module *owner;
+
+	/**
+	 * @unregister:
+	 *
+	 * Called when &drm_device is unregistered. The client should respond by
+	 * releasing it's resources using drm_client_release().
+	 *
+	 * This callback is optional.
+	 */
+	void (*unregister)(struct drm_client_dev *client);
+
+	/**
+	 * @restore:
+	 *
+	 * Called on drm_lastclose(). The first client instance in the list that
+	 * returns zero gets the privilege to restore and no more clients are
+	 * called. This callback is not called after @unregister has been called.
+	 *
+	 * This callback is optional.
+	 */
+	int (*restore)(struct drm_client_dev *client);
+
+	/**
+	 * @hotplug:
+	 *
+	 * Called on drm_kms_helper_hotplug_event().
+	 * This callback is not called after @unregister has been called.
+	 *
+	 * This callback is optional.
+	 */
+	int (*hotplug)(struct drm_client_dev *client);
+};
+
+/**
+ * struct drm_client_dev - DRM client instance
+ */
+struct drm_client_dev {
+	/**
+	 * @dev: DRM device
+	 */
+	struct drm_device *dev;
+
+	/**
+	 * @name: Name of the client.
+	 */
+	const char *name;
+
+	/**
+	 * @list:
+	 *
+	 * List of all clients of a DRM device, linked into
+	 * &drm_device.clientlist. Protected by &drm_device.clientlist_mutex.
+	 */
+	struct list_head list;
+
+	/**
+	 * @funcs: DRM client functions (optional)
+	 */
+	const struct drm_client_funcs *funcs;
+
+	/**
+	 * @file: DRM file
+	 */
+	struct drm_file *file;
+};
+
+int drm_client_new(struct drm_device *dev, struct drm_client_dev *client,
+		   const char *name, const struct drm_client_funcs *funcs);
+void drm_client_release(struct drm_client_dev *client);
+
+void drm_client_dev_unregister(struct drm_device *dev);
+void drm_client_dev_hotplug(struct drm_device *dev);
+void drm_client_dev_restore(struct drm_device *dev);
+
+/**
+ * struct drm_client_buffer - DRM client buffer
+ */
+struct drm_client_buffer {
+	/**
+	 * @client: DRM client
+	 */
+	struct drm_client_dev *client;
+
+	/**
+	 * @handle: Buffer handle
+	 */
+	u32 handle;
+
+	/**
+	 * @pitch: Buffer pitch
+	 */
+	u32 pitch;
+
+	/**
+	 * @gem: GEM object backing this buffer
+	 */
+	struct drm_gem_object *gem;
+
+	/**
+	 * @vaddr: Virtual address for the buffer
+	 */
+	void *vaddr;
+
+	/**
+	 * @fb: DRM framebuffer
+	 */
+	struct drm_framebuffer *fb;
+};
+
+struct drm_client_buffer *
+drm_client_framebuffer_create(struct drm_client_dev *client, u32 width, u32 height, u32 format);
+void drm_client_framebuffer_delete(struct drm_client_buffer *buffer);
+
+#endif

include/drm/drm_device.h

@@ -74,6 +74,27 @@ struct drm_device {
 	struct mutex filelist_mutex;
 	struct list_head filelist;
 
+	/**
+	 * @filelist_internal:
+	 *
+	 * List of open DRM files for in-kernel clients. Protected by @filelist_mutex.
+	 */
+	struct list_head filelist_internal;
+
+	/**
+	 * @clientlist_mutex:
+	 *
+	 * Protects @clientlist access.
+	 */
+	struct mutex clientlist_mutex;
+
+	/**
+	 * @clientlist:
+	 *
+	 * List of in-kernel clients. Protected by @clientlist_mutex.
+	 */
+	struct list_head clientlist;
+
 	/** \name Memory management */
 	/*@{ */
 	struct list_head maplist;	/**< Linked list of regions */