Re: [PATCH] drm/i915: Re-enable rc6 w/fix

[Ben Widawsky <ben@bwidawsk.net>]

On Mon, Mar 14, 2011 at 10:00:20PM -0700, Ben Widawsky wrote:
> On Mon, Mar 14, 2011 at 09:55:01PM -0700, Ben Widawsky wrote:
> > This fixes a race condition with MI_SET_CONTEXT and setting of the
> > PWRCTXA register. If PWRCTXA ends up getting set before MI_SET_CONTEXT
> > completes, it's possible that the system will enter rc6, and try to
> > return to the default render context, which if unset, could cause a GPU
> > hang
> > 
> > Resolve https://bugzilla.kernel.org/show_bug.cgi?id=28582
> 
> I'm still waiting for feedback on bugzilla if this patch works like the
> previous. Just submitting it here for review while we wait...

It appears that I've jumped the gun on this fix. I can sort of reason
that the LOAD_REGISTER_IMM doesn't work, perhaps because somehow the
MI_SET_CONTEXT is really slow, and the GPU executes the register load
out of order, thus invoking the original potential race.

But I followed up with the i915_gpu_idle(), and that too did not work...

Anyone have any ideas?

Ben