[Intel-gfx] [PATCH 0/3] drm/i915: Handle hanging during nonblocking modeset correctly.

[Chris Wilson]

On Thu, Jan 26, 2017 at 04:59:21PM +0100, Maarten Lankhorst wrote:
> When writing some testcases for nonblocking modesets. I found out that the
> infinite wait on the old fb was causing issues.

The crux of the issue here is the locked wait for old dependencies and
the inability to inject the intel_prepare_reset disabling of all planes.
There are a couple of locked waits on struct_mutex within the modeset
locks for intel_overlay and if we happen to be using the display plane
for the first time.

The first I suggested solving using fences to track dependencies and
keep the order between atomic states. Cancelling the outstanding
modesets, replacing with a disable and then on restore jumping to the
final state look doable. It also requires avoiding the struct_mutex for
disabling, which is quite easy. To avoid the wait under struct_mutex,
we've talked about switching to mmio, but for starters we could move the
wait from inside intel_overlay into the fence for the atomic operation.
(But's that a little more surgery than we would like for intel_overlay I
guess - dig out Ville's patches for overlay planes?) And to prevent the
wait under struct_mutex for pin_to_display_plane, my plane is to move
that to an async fenced operation that is then naturally waited upon by
the atomic modeset.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre