[PATCH 5/5] drm/tegra: Implement page-flipping support

[Daniel Vetter]

On Wed, Jan 16, 2013 at 11:01 AM, Thierry Reding
<thierry.reding at avionic-design.de> wrote:
> drm_events_release() should be enough to clean up the events, but I
> suspect the reason why Laurent put that code in was that the drm_crtc
> private data still has a reference to the event and needs to clear it.
> Otherwise the next page flip won't be scheduled because .page_flip()
> would return -EBUSY.

Hm, indeed we seem to have a nice bug in most drivers there :(

> However, it seems like {tegra_dc,shmob_drm_crtc}_cancel_page_flip()
> could both be simplified a lot and just set their event to NULL. Then
> again, maybe keeping a separate reference isn't all that useful. Maybe
> the better thing to do here is iterate over the list of pending VBLANK
> events in *_finish_page_flip() and process each of them? That would
> allow more than one user-space process to queue page flips.

I think we need a slightly more generally useful solution, since most
drivers are currently broken. I've read a bit through the code, but
short of refcounting drm events and adding event->file_priv checks at
relevent places I don't see a sane solution ... And even that one is
rather invasive. Do you have an idea? Imo doing the cleanup in each
driver will be rather error-prone, and since usually kms clients wait
for flips to complete, also guaranteed to be little tested.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch