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

[Stéphane Marchesin]

On Tue, Jun 11, 2013 at 3:57 PM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> 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.

I suspect they'd need to be saved/restored at the hw level as well,
which AFAICS isn't happening today...

Stéphane