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

[Rob Clark]

On Wed, Jan 16, 2013 at 6:36 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> 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.

I suppose we could move the *pending_vblank_event to 'struct
drm_crtc'.. I think probably all/most drivers need the same thing
anyway.  If a driver needs to do something special, it could just
never set crtc->pending_vblank_event and instead do it's own cleanup.

BR,
-R

> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
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