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drm/doc: document fallback behaviour for atomic events

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Worst case if the hw can't support completion signalling in a
race-free way we want the event to be too late, not too early.

Text adapted from a proposal from Laurent - the other side of how to
make hw work correctly where it's possible is imo already sufficiently
documented.

v2: Review from Laurent.

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170308141257.12119-7-daniel.vetter@ffwll.ch
This commit is contained in:
Daniel Vetter 2017-03-08 15:12:39 +01:00
parent b0b7d372df
commit 66f8c10003
1 changed files with 6 additions and 0 deletions
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6
include/drm/drm_crtc.h
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@ -204,6 +204,12 @@ struct drm_crtc_state {
* drm_crtc_arm_vblank_event(). See the documentation of that function
* for a detailed discussion of the constraints it needs to be used
* safely.
*
* If the device can't notify of flip completion in a race-free way
* at all, then the event should be armed just after the page flip is
* committed. In the worst case the driver will send the event to
* userspace one frame too late. This doesn't allow for a real atomic
* update, but it should avoid tearing.
*/
struct drm_pending_vblank_event *event;