i915 update to Linux 3.8 ready!

[am_dxer at fastmail.fm]

On Thu, Mar 17, 2016, at 02:16 PM, Ed Maste wrote:
> On 17 March 2016 at 11:20, Ed Maste <emaste at freebsd.org> wrote:
> > On 15 March 2016 at 19:59,  <am_dxer at fastmail.fm> wrote:
> >>
> >> Thank you both for the suggestions. After suspending and resuming the
> >> machine, I find that the power used by the GPU is significantly less.
> >
> > Thank you for testing, and I see the same behaviour on my Thinkpad
> > X220: after loading i915kms.ko only RC6 is nonzero and RC6+ and RC6++
> > remain at zero, while after
> > boot RC6++ is much higher.
> 
> I tried reverting the Sandy Bridge part of the change that was
> identified as the source of the similar problem in Linux, and it fixes
> the power consumption issue for me.
> 
> My partial revert is just removes the write to the GEN6_MBCTL register
> in gen6_init_clock_gating(). Of course there's some reason it was
> added in Linux, but the driver was functional on Sandy Bridge and
> earlier hardware for years prior to the recent FreeBSD i915 update,
> without that register write. Thus I think it's reasonable to disable
> it until we either fully understand the problem or (more likely) just
> update to a later Linux i915 version and verify normal Sandy Bridge
> power consumption.
> 
> The patch: https://people.freebsd.org/~emaste/D5665.diff
> 
> Code review: https://reviews.freebsd.org/D5665

I applied your patch today and compiled a new kernel. The power
consumption in the EliteBook is also back to normal after loading the
i915kms driver. Suspending and resuming the machine is no longer
required. Thank you for the help and suggestions and for solving this
issue.