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drm: add some comments to drm_wait_vblank and drm_queue_vblank_event 

during the review of the fix for locks problems in drm_wait_vblank,
a couple of false concerns were raised about how the drm_vblank_get
and drm_vblank_put are used in this function; it turned out that the
code is correct and that it cannot be simplified

add a few comments to explain non-obvious flows in the code,
to prevent "false alarms" in the future

v2: incorporate comments received from Daniel Vetter

Signed-off-by: Ilija Hadzic <ihadzic@research.bell-labs.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
This commit is contained in:
Ilija Hadzic 2011-10-31 13:11:57 -04:00 committed by Dave Airlie
parent bfba165826
commit a6778e9e7f
1 changed files with 6 additions and 1 deletions
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7
drivers/gpu/drm/drm_irq.c
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@ -1125,6 +1125,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, int pipe,
trace_drm_vblank_event_delivered(current->pid, pipe,
vblwait->request.sequence);
} else {
/* drm_handle_vblank_events will call drm_vblank_put */
list_add_tail(&e->base.link, &dev->vblank_event_list);
vblwait->reply.sequence = vblwait->request.sequence;
}
@ -1205,8 +1206,12 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
goto done;
}
if (flags & _DRM_VBLANK_EVENT)
if (flags & _DRM_VBLANK_EVENT) {
/* must hold on to the vblank ref until the event fires
* drm_vblank_put will be called asynchronously
*/
return drm_queue_vblank_event(dev, crtc, vblwait, file_priv);
}
if ((flags & _DRM_VBLANK_NEXTONMISS) &&
(seq - vblwait->request.sequence) <= (1<<23)) {