[Intel-gfx] drm/atomic: Reject events for inactive crtc's.

[Daniel Stone]

Hi,

On 6 August 2015 at 13:49, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Thu, Aug 06, 2015 at 01:19:35PM +0200, Maarten Lankhorst wrote:
>> Op 06-08-15 om 11:47 schreef Daniel Stone:
>> > On 30 July 2015 at 08:03, Maarten Lankhorst
>> > <maarten.lankhorst at linux.intel.com> wrote:
>> >> +       if (!state->active && state->event) {
>> >> +               DRM_DEBUG_ATOMIC("[CRTC:%d] requesting event and not active\n",
>> >> +                                crtc->base.id);
>> >> +               return -EINVAL;
>> >> +       }
>> > Hmm, even if disabling? Maybe (!crtc->state->active && !state->active)
>> > && state->event.
>> How do you want to send a vblank event after disabling?
>
> The event would be when we stop scanning out, but yeah that's a bit a
> tricky one. I guess for now (until we have someone who needs this) we
> could just merge Maarten's patch as the easier thing to do right now?
> Maybe with a small code comment that this is intentional?

Exactly that. Surely this (when the CRTC actually goes dark) is
something we already know? Assuming you don't have atomic_disable /
instant-scanout-stop, and have to wait until the next vblank to kill
it, then how does this work?
  - create FB
  - assign FB to plane on CRTC
  - unreference FB such that plane holds the last remaining reference
  - set plane->fb == NULL + crtc->active = 0, i.e. SetCrtc(NULL, 0, 0,
0, 0, ...)

You can't immediately unpin/destroy the FB since you might still be
mid-scanout. So you already need to defer this, and that would be the
point at which you stop scanout. In a lot of hardware, this is just
another latched register which takes effect on the next vblank, for
which you still catch an IRQ - at which point you send the event. If
you actually have atomic_disable hardware that stops scanout
immediately, you can just send the event immediately.

What am I missing?

Cheers,
Daniel