Re: [PATCH 3/3] drm/i915: fix infinite loop at gen6_update_ring_freq

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Apr 01, 2014 at 07:39:49PM -0300, Paulo Zanoni wrote:
> From: Paulo Zanoni <paulo.r.zanoni@intel.com>
> 
> If I boot my Broadwell machine to X on a system with Mesa Gallium
> llvmpipe instead of i965, then kill X and try to run pm_pc8.c, when we
> disable PC8 and call gen6_update_ring_freq(), we will get stuck on an
> infinite loop because the frequencies are zero and the variables are
> unsigned. This happens because we never ran any batch, so we did not
> enable RC6, so the variables are zero. If I run gem_exec_nop before
> running pm_pc8, everything works as expected because gem_exec_nop
> makes RC6 be enabled.
> 
> This commit should prevent the infinite loop, which IMHO is already a
> good reason to be merged, but it is not the proper fix to the "RC6 is
> not being enabled" problem.
> 
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>

This will be fixed (I hope at least) once we have the in-kernel 3d state
emission stuff.

But there's still a race when we go into runtime suspend right after
coming out of system resume. I think we need to grab a runtime pm
reference when we launch the delayed rps work and drop it once that has
run. Or at least we need to have a flush_delayed_work in the runtime pm
suspend function.

There's probably piles more stuff like this.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch