Re: [PATCH] drm/i915: fix long-standing SNB regression in power consumption after resume

From: Daniel Vetter <daniel@ffwll.ch>
To: Chris Wilson <chris@chris-wilson.co.uk>,
	Konstantin Khlebnikov <khlebnikov@openvz.org>,
	David Airlie <airlied@linux.ie>,
	intel-gfx <intel-gfx@lists.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH] drm/i915: fix long-standing SNB regression in power consumption after resume
Date: Tue, 16 Jul 2013 13:13:43 +0200	[thread overview]
Message-ID: <CAKMK7uFyu74z5+EFJHdXxHaaVHN=YG89Ak2obZ_hubxam+1G5w@mail.gmail.com> (raw)
In-Reply-To: <20130716083140.GK2823@cantiga.alporthouse.com>

On Tue, Jul 16, 2013 at 10:31 AM, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> On Tue, Jul 16, 2013 at 09:44:59AM +0200, Daniel Vetter wrote:
>> The issue I have with the current patch is that it looks a bit like
>> duct-tape since the point where we drop the forcewake references seems to
>> lack justification. The write to MBCTL itself will temporarily wake up the
>> chip, so just wrapping that up in with forcewake is very likely not good
>> enough. So I fear that we'll only hold forcewake long enough on most
>> systems and still have a bunch of oddball broken systems out there.
>>
>> Holding forcewake otoh until we've fully set up rps/rc6 makes imo tons of
>> sense, hence why I've brought up the idea. Same reasoning applies to
>> extending the w/a to all systems supporting rc6.
>
> In which case disable rc6 at the start of init gating and only enable it
> at the end of the deferred task. That I think will better test your
> hypothesis and make the transistion steps clearer.

Hm yeah, that would be much clearer instead of risky tricks with a
refcount which is only dropped someplace completely else.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch