Commit c7a47229 authored by Simon Ser's avatar Simon Ser
Browse files

drm/syncobj: add IOCTL to register an eventfd 

Introduce a new DRM_IOCTL_SYNCOBJ_EVENTFD IOCTL which signals an
eventfd from a syncobj.

This is useful for Wayland compositors to handle wait-before-submit.
Wayland clients can send a timeline point to the compositor
before the point has materialized yet, then compositors can wait
for the point to materialize via this new IOCTL.

The existing DRM_IOCTL_SYNCOBJ_TIMELINE_WAIT IOCTL is not suitable
because it blocks. Compositors want to integrate the wait with
their poll(2)-based event loop.

Requirements for new uAPI:

- User-space patch: https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/4262
- IGT: https://lists.freedesktop.org/archives/igt-dev/2023-July/057893.html



v2:
- Wait for fence when flags is zero
- Improve documentation (Pekka)
- Rename IOCTL (Christian)
- Fix typo in drm_syncobj_add_eventfd() (Christian)

v3:
- Link user-space + IGT patches
- Add reference from overview docs

v4: fix IOCTL number conflict with GETFB2 (Nicholas Choi, Vitaly Prosyak)

Signed-off-by: default avatarSimon Ser <contact@emersion.fr>
Reviewed-by: default avatarChristian König <christian.koenig@amd.com>
Acked-by: default avatarPekka Paalanen <pekka.paalanen@collabora.com>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Cc: Daniel Stone <daniel@fooishbar.org>
Cc: James Jones <jajones@nvidia.com>
Cc: Austin Shafer <ashafer@nvidia.com>
Cc: Vitaly Prosyak <vprosyak@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230714111257.11940-1-contact@emersion.fr
parent 4f66feea

drivers/gpu/drm/drm_internal.h

+2 −0
Original line number Diff line number Diff line
@@ -245,6 +245,8 @@ int drm_syncobj_wait_ioctl(struct drm_device *dev, void *data, 
			   struct drm_file *file_private);

int drm_syncobj_timeline_wait_ioctl(struct drm_device *dev, void *data,

				    struct drm_file *file_private);

int drm_syncobj_eventfd_ioctl(struct drm_device *dev, void *data,

			      struct drm_file *file_private);

int drm_syncobj_reset_ioctl(struct drm_device *dev, void *data,

			    struct drm_file *file_private);

int drm_syncobj_signal_ioctl(struct drm_device *dev, void *data,

drivers/gpu/drm/drm_ioctl.c

+2 −0
Original line number Diff line number Diff line
@@ -701,6 +701,8 @@ static const struct drm_ioctl_desc drm_ioctls[] = { 
		      DRM_RENDER_ALLOW),

	DRM_IOCTL_DEF(DRM_IOCTL_SYNCOBJ_TIMELINE_WAIT, drm_syncobj_timeline_wait_ioctl,

		      DRM_RENDER_ALLOW),

	DRM_IOCTL_DEF(DRM_IOCTL_SYNCOBJ_EVENTFD, drm_syncobj_eventfd_ioctl,

		      DRM_RENDER_ALLOW),

	DRM_IOCTL_DEF(DRM_IOCTL_SYNCOBJ_RESET, drm_syncobj_reset_ioctl,

		      DRM_RENDER_ALLOW),

	DRM_IOCTL_DEF(DRM_IOCTL_SYNCOBJ_SIGNAL, drm_syncobj_signal_ioctl,

drivers/gpu/drm/drm_syncobj.c

+142 −6
Original line number Diff line number Diff line
@@ -136,6 +136,10 @@ 
 * requirement is inherited from the wait-before-signal behavior required by

 * the Vulkan timeline semaphore API.

 *

 * Alternatively, &DRM_IOCTL_SYNCOBJ_EVENTFD can be used to wait without

 * blocking: an eventfd will be signaled when the syncobj is. This is useful to

 * integrate the wait in an event loop.

 *

 *

 * Import/export of syncobjs

 * -------------------------
@@ -185,6 +189,7 @@ 


#include <linux/anon_inodes.h>

#include <linux/dma-fence-unwrap.h>

#include <linux/eventfd.h>

#include <linux/file.h>

#include <linux/fs.h>

#include <linux/sched/signal.h>
@@ -212,6 +217,20 @@ struct syncobj_wait_entry { 
static void syncobj_wait_syncobj_func(struct drm_syncobj *syncobj,

				      struct syncobj_wait_entry *wait);



struct syncobj_eventfd_entry {

	struct list_head node;

	struct dma_fence *fence;

	struct dma_fence_cb fence_cb;

	struct drm_syncobj *syncobj;

	struct eventfd_ctx *ev_fd_ctx;

	u64 point;

	u32 flags;

};



static void

syncobj_eventfd_entry_func(struct drm_syncobj *syncobj,

			   struct syncobj_eventfd_entry *entry);



/**

 * drm_syncobj_find - lookup and reference a sync object.

 * @file_private: drm file private pointer
@@ -274,6 +293,28 @@ static void drm_syncobj_remove_wait(struct drm_syncobj *syncobj, 
	spin_unlock(&syncobj->lock);

}



static void

syncobj_eventfd_entry_free(struct syncobj_eventfd_entry *entry)

{

	eventfd_ctx_put(entry->ev_fd_ctx);

	dma_fence_put(entry->fence);

	/* This happens either inside the syncobj lock, or after the node has

	 * already been removed from the list.

	 */

	list_del(&entry->node);

	kfree(entry);

}



static void

drm_syncobj_add_eventfd(struct drm_syncobj *syncobj,

			struct syncobj_eventfd_entry *entry)

{

	spin_lock(&syncobj->lock);

	list_add_tail(&entry->node, &syncobj->ev_fd_list);

	syncobj_eventfd_entry_func(syncobj, entry);

	spin_unlock(&syncobj->lock);

}



/**

 * drm_syncobj_add_point - add new timeline point to the syncobj

 * @syncobj: sync object to add timeline point do
@@ -288,7 +329,8 @@ void drm_syncobj_add_point(struct drm_syncobj *syncobj, 
			   struct dma_fence *fence,

			   uint64_t point)

{

	struct syncobj_wait_entry *cur, *tmp;

	struct syncobj_wait_entry *wait_cur, *wait_tmp;

	struct syncobj_eventfd_entry *ev_fd_cur, *ev_fd_tmp;

	struct dma_fence *prev;



	dma_fence_get(fence);
@@ -302,8 +344,10 @@ void drm_syncobj_add_point(struct drm_syncobj *syncobj, 
	dma_fence_chain_init(chain, prev, fence, point);

	rcu_assign_pointer(syncobj->fence, &chain->base);



	list_for_each_entry_safe(cur, tmp, &syncobj->cb_list, node)

		syncobj_wait_syncobj_func(syncobj, cur);

	list_for_each_entry_safe(wait_cur, wait_tmp, &syncobj->cb_list, node)

		syncobj_wait_syncobj_func(syncobj, wait_cur);

	list_for_each_entry_safe(ev_fd_cur, ev_fd_tmp, &syncobj->ev_fd_list, node)

		syncobj_eventfd_entry_func(syncobj, ev_fd_cur);

	spin_unlock(&syncobj->lock);



	/* Walk the chain once to trigger garbage collection */
@@ -323,7 +367,8 @@ void drm_syncobj_replace_fence(struct drm_syncobj *syncobj, 
			       struct dma_fence *fence)

{

	struct dma_fence *old_fence;

	struct syncobj_wait_entry *cur, *tmp;

	struct syncobj_wait_entry *wait_cur, *wait_tmp;

	struct syncobj_eventfd_entry *ev_fd_cur, *ev_fd_tmp;



	if (fence)

		dma_fence_get(fence);
@@ -335,8 +380,10 @@ void drm_syncobj_replace_fence(struct drm_syncobj *syncobj, 
	rcu_assign_pointer(syncobj->fence, fence);



	if (fence != old_fence) {

		list_for_each_entry_safe(cur, tmp, &syncobj->cb_list, node)

			syncobj_wait_syncobj_func(syncobj, cur);

		list_for_each_entry_safe(wait_cur, wait_tmp, &syncobj->cb_list, node)

			syncobj_wait_syncobj_func(syncobj, wait_cur);

		list_for_each_entry_safe(ev_fd_cur, ev_fd_tmp, &syncobj->ev_fd_list, node)

			syncobj_eventfd_entry_func(syncobj, ev_fd_cur);

	}



	spin_unlock(&syncobj->lock);
@@ -472,7 +519,13 @@ void drm_syncobj_free(struct kref *kref) 
	struct drm_syncobj *syncobj = container_of(kref,

						   struct drm_syncobj,

						   refcount);

	struct syncobj_eventfd_entry *ev_fd_cur, *ev_fd_tmp;



	drm_syncobj_replace_fence(syncobj, NULL);



	list_for_each_entry_safe(ev_fd_cur, ev_fd_tmp, &syncobj->ev_fd_list, node)

		syncobj_eventfd_entry_free(ev_fd_cur);



	kfree(syncobj);

}

EXPORT_SYMBOL(drm_syncobj_free);
@@ -501,6 +554,7 @@ int drm_syncobj_create(struct drm_syncobj **out_syncobj, uint32_t flags, 


	kref_init(&syncobj->refcount);

	INIT_LIST_HEAD(&syncobj->cb_list);

	INIT_LIST_HEAD(&syncobj->ev_fd_list);

	spin_lock_init(&syncobj->lock);



	if (flags & DRM_SYNCOBJ_CREATE_SIGNALED) {
@@ -1304,6 +1358,88 @@ drm_syncobj_timeline_wait_ioctl(struct drm_device *dev, void *data, 
	return ret;

}



static void syncobj_eventfd_entry_fence_func(struct dma_fence *fence,

					     struct dma_fence_cb *cb)

{

	struct syncobj_eventfd_entry *entry =

		container_of(cb, struct syncobj_eventfd_entry, fence_cb);



	eventfd_signal(entry->ev_fd_ctx, 1);

	syncobj_eventfd_entry_free(entry);

}



static void

syncobj_eventfd_entry_func(struct drm_syncobj *syncobj,

			   struct syncobj_eventfd_entry *entry)

{

	int ret;

	struct dma_fence *fence;



	/* This happens inside the syncobj lock */

	fence = dma_fence_get(rcu_dereference_protected(syncobj->fence, 1));

	ret = dma_fence_chain_find_seqno(&fence, entry->point);

	if (ret != 0 || !fence) {

		dma_fence_put(fence);

		return;

	}



	list_del_init(&entry->node);

	entry->fence = fence;



	if (entry->flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE) {

		eventfd_signal(entry->ev_fd_ctx, 1);

		syncobj_eventfd_entry_free(entry);

	} else {

		ret = dma_fence_add_callback(fence, &entry->fence_cb,

					     syncobj_eventfd_entry_fence_func);

		if (ret == -ENOENT) {

			eventfd_signal(entry->ev_fd_ctx, 1);

			syncobj_eventfd_entry_free(entry);

		}

	}

}



int

drm_syncobj_eventfd_ioctl(struct drm_device *dev, void *data,

			  struct drm_file *file_private)

{

	struct drm_syncobj_eventfd *args = data;

	struct drm_syncobj *syncobj;

	struct eventfd_ctx *ev_fd_ctx;

	struct syncobj_eventfd_entry *entry;



	if (!drm_core_check_feature(dev, DRIVER_SYNCOBJ_TIMELINE))

		return -EOPNOTSUPP;



	if (args->flags & ~DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE)

		return -EINVAL;



	if (args->pad)

		return -EINVAL;



	syncobj = drm_syncobj_find(file_private, args->handle);

	if (!syncobj)

		return -ENOENT;



	ev_fd_ctx = eventfd_ctx_fdget(args->fd);

	if (IS_ERR(ev_fd_ctx))

		return PTR_ERR(ev_fd_ctx);



	entry = kzalloc(sizeof(*entry), GFP_KERNEL);

	if (!entry) {

		eventfd_ctx_put(ev_fd_ctx);

		return -ENOMEM;

	}

	entry->syncobj = syncobj;

	entry->ev_fd_ctx = ev_fd_ctx;

	entry->point = args->point;

	entry->flags = args->flags;



	drm_syncobj_add_eventfd(syncobj, entry);

	drm_syncobj_put(syncobj);



	return 0;

}



int

drm_syncobj_reset_ioctl(struct drm_device *dev, void *data,

include/drm/drm_syncobj.h

+5 −1
Original line number Diff line number Diff line
@@ -54,7 +54,11 @@ struct drm_syncobj { 
	 */

	struct list_head cb_list;

	/**

	 * @lock: Protects &cb_list and write-locks &fence.

	 * @ev_fd_list: List of registered eventfd.

	 */

	struct list_head ev_fd_list;

	/**

	 * @lock: Protects &cb_list and &ev_fd_list, and write-locks &fence.

	 */

	spinlock_t lock;

	/**

include/uapi/drm/drm.h

+23 −0
Original line number Diff line number Diff line
@@ -909,6 +909,27 @@ struct drm_syncobj_timeline_wait { 
	__u32 pad;

};



/**

 * struct drm_syncobj_eventfd

 * @handle: syncobj handle.

 * @flags: Zero to wait for the point to be signalled, or

 *         &DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE to wait for a fence to be

 *         available for the point.

 * @point: syncobj timeline point (set to zero for binary syncobjs).

 * @fd: Existing eventfd to sent events to.

 * @pad: Must be zero.

 *

 * Register an eventfd to be signalled by a syncobj. The eventfd counter will

 * be incremented by one.

 */

struct drm_syncobj_eventfd {

	__u32 handle;

	__u32 flags;

	__u64 point;

	__s32 fd;

	__u32 pad;

};





struct drm_syncobj_array {

	__u64 handles;
@@ -1169,6 +1190,8 @@ extern "C" { 
 */

#define DRM_IOCTL_MODE_GETFB2		DRM_IOWR(0xCE, struct drm_mode_fb_cmd2)



#define DRM_IOCTL_SYNCOBJ_EVENTFD	DRM_IOWR(0xCF, struct drm_syncobj_eventfd)



/*

 * Device specific ioctls should only be in their respective headers

 * The device specific ioctl range is from 0x40 to 0x9f.