On Tue, 30 Aug 2022 17:29:35 +0000
Simon Ser <contact@xxxxxxxxxxx> wrote:
> 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.
>
> v2: document new uAPI
>
> Signed-off-by: Simon Ser <contact@xxxxxxxxxxx>
> Co-developed-by: André Almeida <andrealmeid@xxxxxxxxxx>
> Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Joshua Ashton <joshua@xxxxxxxxx>
> Cc: Melissa Wen <mwen@xxxxxxxxxx>
> Cc: Alex Deucher <alexander.deucher@xxxxxxx>
> Cc: Harry Wentland <hwentlan@xxxxxxx>
> Cc: Nicholas Kazlauskas <nicholas.kazlauskas@xxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_atomic_uapi.c | 28 +++++++++++++++++++++++++---
> include/uapi/drm/drm_mode.h | 4 ++++
> 2 files changed, 29 insertions(+), 3 deletions(-)
...
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index 86a292c3185a..cce1a1bea645 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -942,6 +942,10 @@ 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.
> */
> #define DRM_MODE_PAGE_FLIP_ASYNC 0x02
> #define DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE 0x4
Hi Simon,
recalling what Ville explained that enabling async flips might require
one more sync flip first, how is that supposed to work?
A TEST_ONLY commit is not allowed to change hardware state, and a
failing real commit is not allowed to change hardware state either
(right?), therefore a failing async flip cannot prepare the next flip
to be async, meaning async will never work.
Thanks,
pq
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