Re: [PATCH 1/6] drm/i915: grab force_wake when restoring LCPLL

[Ben Widawsky <ben@bwidawsk.net>]

On Mon, Aug 19, 2013 at 04:01:13PM -0300, Paulo Zanoni wrote:
> From: Paulo Zanoni <paulo.r.zanoni@intel.com>
> 
> If LCPLL is disabled, there's a chance we might be in package C8 state
> or deeper, and we'll get a hard hang when restoring LCPLL (also, a red
> led lights up on my motherboard). So grab the force_wake, which will
> get us out of RC6 and, as a consequence, out of PC8+ (since we need
> RC6 to get into PC8+).
> 
> v2: Call the correct force_wake interface.
> 
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>

Hi Paulo. As I recall, the steps in the bspec are laid out exactly so we
don't have to call forcewake. I think the explanation sounds a little
fishy.

Specifically, I thought D_COMP COMP_FORCE + waiting for PLL lock was
sufficient. If it's not, I worry you're papering over another bug, or
incorrect bspec sequence.

Not opposed to the patch in the meanwhile, but it just feels a little
unsafe to me.

-- 
Ben Widawsky, Intel Open Source Technology Center