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

[James Bottomley]

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.
> 
> This should be easy enough to try before bisecting:
> http://patchwork.freedesktop.org/patch/msgid/1466162081-12042-1-git-s
> end-email-mika.kahola at intel.com

I'll try that.  You should know this platform has a firmware bug in the
digital signals across the display port ... some problem with the mux
in the thunderbolt.  Unfortunately the microcode update for this (the
thunderbolt firmware) can't be applied from Linux or even the usual
FreeDOS, so I'm a bit stuck.

It's also been pointed out to me off list that there's a lot of Skylake
errata that have display flicker due to non-graphics issues:

http://www.intel.com/content/www/us/en/processors/core/desktop-6th-gen-core-family-spec-update.html

My system is a Dell XPS 9350 and I have updated it with the just released firmware:

http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=VNT5J

Which causes my cpu microcode version to go from

> [    2.314472] microcode: CPU0 sig=0x406e3, pf=0x80, revision=0x82

to

> [    2.264669] microcode: CPU0 sig=0x406e3, pf=0x80, revision=0x8a

But thanks to the completely opaque microcode update process via the
OEMs it's not clear whether this is sufficient to fix the errata that
are listed as causing flicker (the reported revision on current skylake
lenovos seems to be 0x94)

James