On Sun, Mar 05, 2017 at 03:10:32AM +0200, Laurent Pinchart wrote:
The page flip event is armed in the atomic begin handler, creating a race condition with the frame end interrupt that could send the event before the atomic operation actually completes. To avoid that, arm the event in the atomic flush handler after queuing the page flip.
This change doesn't fully close the race window, as the frame end interrupt could be generated before the page flip is committed to hardware but only handled after the event is armed. However, the race window is now much smaller.
The event must however be armed before calling the VSP atomic commit function, otherwise the completion callback could arrive before we arm the event, resulting in a deadlock.
Signed-off-by: Laurent Pinchart laurent.pinchart+renesas@ideasonboard.com
Since your hw is not the only one where this seems fundamentally unfixable, should we document a recommended way to handle/minize the race window? -Daniel
drivers/gpu/drm/rcar-du/rcar_du_crtc.c | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-)
Changes since v1:
- Arm the event before calling the VSP atomic commit function
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c index 7391dd95c733..2aceb84fc15d 100644 --- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c +++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c @@ -502,17 +502,6 @@ static void rcar_du_crtc_atomic_begin(struct drm_crtc *crtc, struct drm_crtc_state *old_crtc_state) { struct rcar_du_crtc *rcrtc = to_rcar_crtc(crtc);
struct drm_device *dev = rcrtc->crtc.dev;
unsigned long flags;
if (crtc->state->event) {
WARN_ON(drm_crtc_vblank_get(crtc) != 0);spin_lock_irqsave(&dev->event_lock, flags);rcrtc->event = crtc->state->event;crtc->state->event = NULL;spin_unlock_irqrestore(&dev->event_lock, flags);}
if (rcar_du_has(rcrtc->group->dev, RCAR_DU_FEATURE_VSP1_SOURCE)) rcar_du_vsp_atomic_begin(rcrtc);
@@ -522,9 +511,20 @@ static void rcar_du_crtc_atomic_flush(struct drm_crtc *crtc, struct drm_crtc_state *old_crtc_state) { struct rcar_du_crtc *rcrtc = to_rcar_crtc(crtc);
struct drm_device *dev = rcrtc->crtc.dev;
unsigned long flags;
rcar_du_crtc_update_planes(rcrtc);
if (crtc->state->event) {
WARN_ON(drm_crtc_vblank_get(crtc) != 0);spin_lock_irqsave(&dev->event_lock, flags);rcrtc->event = crtc->state->event;crtc->state->event = NULL;spin_unlock_irqrestore(&dev->event_lock, flags);}
if (rcar_du_has(rcrtc->group->dev, RCAR_DU_FEATURE_VSP1_SOURCE)) rcar_du_vsp_atomic_flush(rcrtc);
}
Regards,
Laurent Pinchart
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