[PATCH] drm-vblank: Always return true vblank count of scheduled vblank event.

Mario Kleiner mario.kleiner at tuebingen.mpg.de
Fri Dec 10 07:00:19 PST 2010

-------- Original Message --------
Subject: [PATCH] drm-vblank: Always return true vblank count of 
scheduled vblank event.
Date: Fri, 10 Dec 2010 15:58:10 +0100
From: Mario Kleiner <mario.kleiner at tuebingen.mpg.de>
To: airlied at gmail.com
CC: jbarnes at virtuousgeek.org,	krh at bitplanet.net,	Mario Kleiner 
<mario.kleiner at tuebingen.mpg.de>

This patch tries to make sure that the vbl.reply.sequence
vblank count for a queued or emitted vblank event always
corresponds to the true vblank count of queueing/emission, so
the ddx can rely on the returned target_msc for consistency
checks and implementation of swap_intervals in glXSwapBuffers().

Without this there is a small race-condition between the
userspace ddx queueing a vblank event and the vblank
counter incrementing before the event gets queued in
the kernel.

Signed-off-by: Mario Kleiner <mario.kleiner at tuebingen.mpg.de>
  drivers/gpu/drm/drm_irq.c |    3 +++
  1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 4e82d0d..55160d7 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -1086,15 +1086,18 @@ static int drm_queue_vblank_event(struct 
drm_device *dev, int pipe,

  	e->event.sequence = vblwait->request.sequence;
  	if ((seq - vblwait->request.sequence) <= (1 << 23)) {
+		e->event.sequence = seq;
  		e->event.tv_sec = now.tv_sec;
  		e->event.tv_usec = now.tv_usec;
  		drm_vblank_put(dev, e->pipe);
  		list_add_tail(&e->base.link, &e->base.file_priv->event_list);
+		vblwait->reply.sequence = seq;
  		trace_drm_vblank_event_delivered(current->pid, pipe,
  	} else {
  		list_add_tail(&e->base.link, &dev->vblank_event_list);
+		vblwait->reply.sequence = vblwait->request.sequence;

  	spin_unlock_irqrestore(&dev->event_lock, flags);

More information about the dri-devel mailing list