[Intel-gfx] Bad flicker on skylake HQD due to code in the 4.7 merge window

[Jani Nikula]

On Thu, 23 Jun 2016, Steven Newbury <steve at snewbury.org.uk> wrote:
> [ Unknown signature status ]
> On Sun, 2016-06-19 at 14:53 -0700, James Bottomley wrote:
>> On Fri, 2016-06-17 at 16:06 -0700, James Bottomley wrote:
>> > On Fri, 2016-06-17 at 16:34 +0300, Jani Nikula wrote:
>> > > On Fri, 17 Jun 2016, Daniel Vetter <daniel at ffwll.ch> wrote:
>> > > > On Thu, Jun 16, 2016 at 03:42:12PM -0700, James Bottomley
>> > > > wrote:
>> > > > > On Thu, 2016-06-16 at 14:29 -0700, James Bottomley wrote:
>> > > > > > On Thu, 2016-06-16 at 23:24 +0200, Daniel Vetter wrote:
>> > > > > > > I guess we'll need the bisect on this one to make
>> > > > > > > progress.
>> > > > > > 
>> > > > > > Sigh, I was afraid that might be the next step.
>> > > > > 
>> > > > > OK, I have a curious data point.  I assumed the problem would
>> > > > > be
>> > > > > somewhere in the drm update, so I started bisecting that at
>> > > > > the
>> > > > > top. 
>> > > > >  However, the top most commit:
>> > > > > 
>> > > > > commit 1d6da87a3241deb13d073c4125d19ed0e5a0c62c
>> > > > > Merge: 1f40c49 a39ed68
>> > > > > Author: Linus Torvalds <torvalds at linux-foundation.org>
>> > > > > Date:   Mon May 23 11:48:48 2016 -0700
>> > > > > 
>> > > > >     Merge branch 'drm-next' of
>> > > > > git://people.freedesktop.org/~airlied/linux
>> > > > > 
>> > > > > Isn't actually bad.  There's no flicker here, so whatever
>> > > > > caused
>> > > > > the
>> > > > > problem came from some update after this.
>> > > > 
>> > > > There was a fixes pull after this. Might be worth it to
>> > > > restrict
>> > > > to
>> > > > just
>> > > > the i915 changes, which are just
>> > > > 5b4fd5b1111b1230cd037..157d2c7fad0863222
>> > > > 
>> > > > Looking at those nothing seems to stick out which might explain
>> > > > what's
>> > > > happening for you.
>> > 
>> > OK, so just on the firmware, the system seems less flickery with
>> > the
>> > new 1.4.3 UEFI, so I'm starting to think it is a Skylake errata 
>> > issue.  The flicker isn't gone for good, but seems to be reboot 
>> > dependent (it's there in some boots, but gone on a reboot).
>> > 
>> > > This should be easy enough to try before bisecting:
>> > > http://patchwork.freedesktop.org/patch/msgid/1466162081-12042-1-g
>> > > it
>> > > -s
>> > > end-email-mika.kahola at intel.com
>> > 
>> > Applying this didn't seem to make a difference: still there on
>> > some 
>> > and gone on other reboots.
>> 
>> OK, my candidate bad commit is this one:
>> 
>> commit a05628195a0d9f3173dd9aa76f482aef692e46ee
>> Author: Ville Syrjälä <ville.syrjala at linux.intel.com>
>> Date:   Mon Apr 11 10:23:51 2016 +0300
>> 
>>     drm/i915: Get panel_type from OpRegion panel details
>> 
>> After being more careful about waiting to identify flicker, this one
>> seems to be the one the bisect finds.  I'm now running v4.7-rc3 with
>> this one reverted and am currently seeing no flicker problems.  It
>> is,
>> however, early days because the flicker can hide for long periods, so
>> I
>> 'll wait until Monday evening and a few reboots before declaring
>> victory.
>> 
>> 
> I'm seeing this on my IvyBridge.  I'll try reverting the commit here
> too, to see if it's the same issue.

IvyBridge doesn't have low vswing for eDP. If reverting helps, it's a
different failure mode.

BR,
Jani.

-- 
Jani Nikula, Intel Open Source Technology Center