[Intel-gfx] [PATCH 2/2] drm/i915: repin bound framebuffers on resume

[Chris Wilson]

On Tue, Jun 11, 2013 at 03:49:27PM -0700, Stéphane Marchesin wrote:
> During suspend all fences are reset, including their pin_count which
> is reset to 0. However a framebuffer can be bound across
> suspend/resume, which means that when the buffer is unbound after
> resume, the pin count for the buffer will be negative. Since the
> fence pin count is now negative when available and zero when in use,
> the buffer's fence will get recycled when the fence is in use which
> is the opposite of what we want. The visible effect is that since the
> fence is recycled the tiling mode goes away while the buffer is being
> displayed and we get lines/screens of garbage.
> 
> To fix this, we repin the fences for all bound fbs on resume, which
> ensures the pin count is right.

Yikes. So why do we not just keep the fences alive during suspend (not
touching their pin_count), and then just iterate over the list of fences
rewriting the register as required upon resume? That would seem less
error prone than trying to reconstruct the lost pin_count.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre