[PATCH] drm: Don't allow legacy cursor updates to stall others or be stalled

[Chris Wilson]

On Tue, Aug 23, 2016 at 11:48:34AM +0100, Chris Wilson wrote:
> Legacy cursor updates are entirely asynchronous with respect to all
> other users of the atomic pipeline. They neither wait for any
> outstanding flips, nor do they cause subsequent flips to be delayed. The
> only ordering we do require is given by making the legacy cursor update
> nonblocking (so the sequence of userspace calls from a process is
> ordered from the pov of the client).

Hmm, it is also not entirely true. A modeset (reconfiguration of the
pipe size) would require all cursor updates to be flushed, or else we
may make the cursor out-of-bounds which can cause GPU hangs. At the
moment, I think that is governed by the crtc lock and the blocking
nature of the modeset + cursor update. But in the future we want far
more fine grained control over (mostly) asynchronous updates.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre