On Fri, Oct 28, 2011 at 05:44:23PM -0400, Ilija Hadzic wrote:
> 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
>
> Signed-off-by: Ilija Hadzic <ihadzic@xxxxxxxxxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_irq.c | 8 ++++++++
> 1 files changed, 8 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index c8b4da8..e9dd19d 100644
> --- a/drivers/gpu/drm/drm_irq.c
> +++ b/drivers/gpu/drm/drm_irq.c
> @@ -1065,6 +1065,10 @@ out:
> return ret;
> }
>
> +/* must acquire vblank reference count (call drm_vblank_get) */
> +/* before calling this function; the matching drm_vblank_put */
> +/* will either be issued here or in drm_handle_vblank_events */
> +/* after the vblank is signaled */
> static int drm_queue_vblank_event(struct drm_device *dev, int pipe,
> union drm_wait_vblank *vblwait,
> struct drm_file *file_priv)
> @@ -1124,6 +1128,9 @@ static int drm_queue_vblank_event(struct drm_device *dev, int pipe,
> trace_drm_vblank_event_delivered(current->pid, pipe,
> vblwait->request.sequence);
> } else {
> + /* can't call drm_vblank_put here because interrupt */
> + /* must remain enabled until the event occurs */
> + /* drm_handle_vblank_events will do this for us */
> list_add_tail(&e->base.link, &dev->vblank_event_list);
> vblwait->reply.sequence = vblwait->request.sequence;
> }
> @@ -1215,6 +1222,7 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
>
> if (flags & _DRM_VBLANK_EVENT) {
> spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
> + /* drm_queue_vblank_event() will call drm_vblank_put() */
I think three comments for this is a bit overkill. Imo one here at the
only callsite of queue_vblank_event saying that it needs to hold onto the
vblank ref untill the event fires and hence will call drm_vblank_put
asynchronously is good enought.
> return drm_queue_vblank_event(dev, crtc, vblwait, file_priv);
> }
>
> --
> 1.7.7
>
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--
Daniel Vetter
Mail: daniel@xxxxxxxx
Mobile: +41 (0)79 365 57 48
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