From 66f8c10003966130b0b2812fcbdfa6389bccd577 Mon Sep 17 00:00:00 2001 From: Daniel Vetter Date: Wed, 8 Mar 2017 15:12:39 +0100 Subject: [PATCH] drm/doc: document fallback behaviour for atomic events 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 Reviewed-by: Laurent Pinchart Signed-off-by: Daniel Vetter Link: http://patchwork.freedesktop.org/patch/msgid/20170308141257.12119-7-daniel.vetter@ffwll.ch --- include/drm/drm_crtc.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h index cba29ffedafd..6ef59da3fd8e 100644 --- a/include/drm/drm_crtc.h +++ b/include/drm/drm_crtc.h @@ -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; -- 2.20.1