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@xxxxxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_irq.c | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletions(-)
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 3830e9e..79c02da 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -1124,6 +1124,7 @@ 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;
}
@@ -1204,8 +1205,12 @@ 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)) {
--
1.7.7
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