[RFC,v3,3/4] drm/atomic: add ATOMIC_AMEND flag to the Atomic IOCTL.

Submitted by Helen Koike on April 12, 2019, 12:58 p.m.


Message ID 20190412125827.5877-4-helen.koike@collabora.com
State New
Headers show
Series "async vs amend - UAPI" ( rev: 1 ) in DRI devel

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Commit Message

Helen Koike April 12, 2019, 12:58 p.m.
This flag tells core to jump ahead the queued update if the conditions
in drm_atomic_amend_check() are met. That means we are only able to do an
amend update if no modeset is pending and update for the same plane is
not queued.

It uses the already in place infrastructure for amend updates.

It is useful for cursor updates over the atomic ioctl.
Otherwise in some cases updates may be delayed to the point the
user will notice it.
Note that for now it's only enabled for cursor planes.

DRM_MODE_ATOMIC_AMEND should be passed to the Atomic IOCTL to use this

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
[updated for upstream]
Signed-off-by: Helen Koike <helen.koike@collabora.com>

This is the third attempt to introduce the new ATOMIC_AMEND flag for atomic
operations, see the commit message for a more detailed description.
I am sending this patch in the series as an RFC as I still have things
to define/discuss.

The main reasons to expose this through atomic api is to avoid mixing legacy
with modern/atomic API (since their interactions are not well defined)
and to be able to explicitly manage the cursor plane.

The way I envision it working is:

1) userspace just use DRM_MODE_PAGE_FLIP_ASYNC if true async is desired.
2) if it fails, then userspace can try DRM_MODE_ATOMIC_AMEND if true async is
not required, but a legacy cursor behavior is required
3) if amend is not possible, we can or:
        A) fallback to a non amend update
        B) fail
        C) add another flag to define what it should do.

Right now the code does A for legacy cursor and B for atomic api using
Discussing with some people it seems that failing is better for Xorg,
but Ozone (chrome compositor) doesn't expect the amend to fail, but I
think it could just retry the same atomic commit without the AMEND flag
if it wants to fallback.

Alexandros also did a proof-of-concept to use this flag and draw cursors
using atomic if possible on ozone (Chrome compositor) [1].

I'm sending this as an RFC for now as I still need to verify the
requirements from other compositors and make some tests (and also to
justify the s/async/amend renaming).

Please, let me know if you detect issues with this.
If not, I'll start implementing tests in igt and push the adoption in
other compositors.


[1] https://chromium-review.googlesource.com/c/chromium/src/+/1092711
[2] https://gitlab.collabora.com/eballetbo/drm-cursor/commits/async-capability

Changes in v3:
- rebase tree
- rebase on top of renaming async_update to amend_update
- improve documentation
- don't fall back to a normal commit if amend is not possible when
requested through the atomic api

Changes in v2:
- rebase tree
- do not fall back to a non-async update if if there isn't any
pending commit to amend

Changes in v1:
- https://patchwork.freedesktop.org/patch/243088/
- Only enable it if userspace requests it.
- Only allow async update for cursor type planes.

 drivers/gpu/drm/drm_atomic_helper.c | 39 +++++++++++++++++++++++------
 drivers/gpu/drm/drm_atomic_uapi.c   |  8 ++++++
 include/uapi/drm/drm_mode.h         |  9 ++++++-
 3 files changed, 48 insertions(+), 8 deletions(-)

Patch hide | download patch | download mbox

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index eb5dcd84fea7..9b0df08836c3 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -947,10 +947,18 @@  int drm_atomic_helper_check(struct drm_device *dev,
 	if (ret)
 		return ret;
+	/*
+	 * If amend was explicitly requested, but it is not possible,
+	 * return error instead of falling back to a normal commit.
+	 */
+	if (state->amend_update)
+		return drm_atomic_helper_amend_check(dev, state);
+	/* Legacy mode falls back to a normal commit if amend isn't possible. */
 	if (state->legacy_cursor_update)
 		state->amend_update = !drm_atomic_helper_amend_check(dev, state);
-	return ret;
+	return 0;
@@ -1574,12 +1582,20 @@  static void commit_work(struct work_struct *work)
  * The amend feature provides a way to perform 1000 updates to be applied as
  * soon as possible without waiting for 1000 vblanks.
- * Currently, only the legacy cursor update uses amend mode, where historically,
+ * Legacy cursor update uses amend mode, where historically,
  * userspace performs several updates before the next vblank and don't want to
  * see a delay in the cursor's movement.
  * If amend is not supported, legacy cursor falls back to a normal sync update.
- * To implement the legacy cursor update, drivers should provide
+ * Amend can also be performed through the atomic API using the flag
+ * DRM_MODE_ATOMIC_AMEND. The atomic commit will fail if this flag is set but
+ * the driver doesn't support it.
+ * Amend can't perform modeset, thus atomic API will fail if
+ * DRM_MODE_ATOMIC_AMEND is used in conjunction with
+ *
+ * To implement the legacy cursor update and amend mode through atomic, drivers
+ * should provide:
  * &drm_plane_helper_funcs.atomic_amend_check() and
  * &drm_plane_helper_funcs.atomic_amend_update()
@@ -1601,16 +1617,21 @@  static void commit_work(struct work_struct *work)
  * Notes / highlights:
- * - amend update is performed on legacy cursor updates.
+ * - amend update is performed on legacy cursor updates, but it will fallback to
+ *   a normal commit if amend is not possible. However, if amend was requested
+ *   through atomic, the ioctl will fail instead of fall back if it can't be
+ *   amended.
+ *
+ * - atomic api will reject amend if DRM_MODE_ATOMIC_ALLOW_MODESET flag is used.
+ *
+ *   will be ignored.
  * - amend update won't happen if there is an outstanding commit modifying the
  *   same plane.
  * - amend update won't happen if atomic_amend_check() returns false.
- * - if atomic_amend_check() fails, it falls back to a normal synchronous
- *   update.
- *
  * - if userspace wants to ensure an asynchronous page flip, i.e. change hw
  *   state immediately, see DRM_MODE_PAGE_FLIP_ASYNC flag
  *   (asynchronous page flip maintains the amend property by definition).
@@ -1673,6 +1694,10 @@  int drm_atomic_helper_amend_check(struct drm_device *dev,
 	if (new_plane_state->fence)
 		return -EINVAL;
+	/* Only allow amend update for cursor type planes. */
+	if (plane->type != DRM_PLANE_TYPE_CURSOR)
+		return -EINVAL;
 	 * Don't do an amend update if there is an outstanding commit modifying
 	 * the plane.
diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
index 4eb81f10bc54..d1962cdea602 100644
--- a/drivers/gpu/drm/drm_atomic_uapi.c
+++ b/drivers/gpu/drm/drm_atomic_uapi.c
@@ -28,6 +28,7 @@ 
 #include <drm/drm_atomic_uapi.h>
 #include <drm/drm_atomic.h>
+#include <drm/drm_atomic_uapi.h>
 #include <drm/drm_print.h>
 #include <drm/drm_drv.h>
 #include <drm/drm_writeback.h>
@@ -1300,6 +1301,10 @@  int drm_mode_atomic_ioctl(struct drm_device *dev,
 			(arg->flags & DRM_MODE_PAGE_FLIP_EVENT))
 		return -EINVAL;
+	if ((arg->flags & DRM_MODE_ATOMIC_ALLOW_MODESET) &&
+			(arg->flags & DRM_MODE_ATOMIC_AMEND))
+		return -EINVAL;
 	state = drm_atomic_state_alloc(dev);
 	if (!state)
 		return -ENOMEM;
@@ -1307,6 +1312,9 @@  int drm_mode_atomic_ioctl(struct drm_device *dev,
 	drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
 	state->acquire_ctx = &ctx;
 	state->allow_modeset = !!(arg->flags & DRM_MODE_ATOMIC_ALLOW_MODESET);
+	/* async takes precedence over amend */
+	state->amend_update = arg->flags & DRM_MODE_PAGE_FLIP_ASYNC ? 0 :
+					!!(arg->flags & DRM_MODE_ATOMIC_AMEND);
 	copied_objs = 0;
diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index 88ef2cf04d13..3831d04f3b38 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -743,19 +743,26 @@  struct drm_mode_destroy_dumb {
  * Indicates whether a full modeset is acceptable or not.
+ *
+ * Used to perform an atomic amend. See "DOC: amend mode atomic commit" in
+ * drm_atomic_helper.c for more details.
+ * This flag can't be used with DRM_MODE_ATOMIC_ALLOW_MODESET.
 /*  */
+#define DRM_MODE_ATOMIC_AMEND 0x0800
 struct drm_mode_atomic {
 	__u32 flags;