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Subject: [PATCH v4 1/6] drm: allow DRM_MODE_PAGE_FLIP_ASYNC for atomic commits
Date:   Fri, 30 Jun 2023 23:09:12 -0300
Message-ID: <20230701020917.143394-2-andrealmeid@igalia.com>
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From: Simon Ser <contact@emersion.fr>

If the driver supports it, allow user-space to supply the
DRM_MODE_PAGE_FLIP_ASYNC flag to request an async page-flip.
Set drm_crtc_state.async_flip accordingly.

Document that drivers will reject atomic commits if an async
flip isn't possible. This allows user-space to fall back to
something else. For instance, Xorg falls back to a blit.
Another option is to wait as close to the next vblank as
possible before performing the page-flip to reduce latency.

Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Co-developed-by: André Almeida <andrealmeid@igalia.com>
Signed-off-by: André Almeida <andrealmeid@igalia.com>
---
v4: no changes
---
 drivers/gpu/drm/drm_atomic_uapi.c | 28 +++++++++++++++++++++++++---
 include/uapi/drm/drm_mode.h       |  9 +++++++++
 2 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
index d867e7f9f2cd..dfd4cf7169df 100644
--- a/drivers/gpu/drm/drm_atomic_uapi.c
+++ b/drivers/gpu/drm/drm_atomic_uapi.c
@@ -1286,6 +1286,18 @@ static void complete_signaling(struct drm_device *dev,
 	kfree(fence_state);
 }
 
+static void
+set_async_flip(struct drm_atomic_state *state)
+{
+	struct drm_crtc *crtc;
+	struct drm_crtc_state *crtc_state;
+	int i;
+
+	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
+		crtc_state->async_flip = true;
+	}
+}
+
 int drm_mode_atomic_ioctl(struct drm_device *dev,
 			  void *data, struct drm_file *file_priv)
 {
@@ -1326,9 +1338,16 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
 	}
 
 	if (arg->flags & DRM_MODE_PAGE_FLIP_ASYNC) {
-		drm_dbg_atomic(dev,
-			       "commit failed: invalid flag DRM_MODE_PAGE_FLIP_ASYNC\n");
-		return -EINVAL;
+		if (!dev->mode_config.async_page_flip) {
+			drm_dbg_atomic(dev,
+				       "commit failed: DRM_MODE_PAGE_FLIP_ASYNC not supported\n");
+			return -EINVAL;
+		}
+		if (dev->mode_config.atomic_async_page_flip_not_supported) {
+			drm_dbg_atomic(dev,
+				       "commit failed: DRM_MODE_PAGE_FLIP_ASYNC not supported with atomic\n");
+			return -EINVAL;
+		}
 	}
 
 	/* can't test and expect an event at the same time. */
@@ -1426,6 +1445,9 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
 	if (ret)
 		goto out;
 
+	if (arg->flags & DRM_MODE_PAGE_FLIP_ASYNC)
+		set_async_flip(state);
+
 	if (arg->flags & DRM_MODE_ATOMIC_TEST_ONLY) {
 		ret = drm_atomic_check_only(state);
 	} else if (arg->flags & DRM_MODE_ATOMIC_NONBLOCK) {
diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index 46becedf5b2f..56342ba2c11a 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -949,6 +949,15 @@ struct hdr_output_metadata {
  * Request that the page-flip is performed as soon as possible, ie. with no
  * delay due to waiting for vblank. This may cause tearing to be visible on
  * the screen.
+ *
+ * When used with atomic uAPI, the driver will return an error if the hardware
+ * doesn't support performing an asynchronous page-flip for this update.
+ * User-space should handle this, e.g. by falling back to a regular page-flip.
+ *
+ * Note, some hardware might need to perform one last synchronous page-flip
+ * before being able to switch to asynchronous page-flips. As an exception,
+ * the driver will return success even though that first page-flip is not
+ * asynchronous.
  */
 #define DRM_MODE_PAGE_FLIP_ASYNC 0x02
 #define DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE 0x4
-- 
2.41.0