[Intel-gfx] regression bisected: display sync drops after 7221fc33

[dann frazier]

On Tue, Jan 26, 2016 at 08:10:04AM -0700, dann frazier wrote:
> On Tue, Jan 26, 2016 at 01:17:01PM +0200, Ville Syrjälä wrote:
> > On Mon, Jan 25, 2016 at 09:35:26AM -0700, dann frazier wrote:
> > > I've got a Lenovo T410 w/ an external display (DisplayPort<->HDMI). After
> > > upgrading from a 4.2 kernel to a 4.3, I started hitting an issue where
> > > the display thinks it has lost input for a few moments. Oddly, it
> > > usually happens when I start typing in a terminal after a short period
> > > of inactivity.
> > > 
> > > I see no OS-side symptoms - there are no new messages in dmesg/syslog/Xorg
> > > log, etc.
> > 
> > Any fifo underrun reports in dmesg in general?
> 
> Yes, several:
>   [ 1886.547409] [drm:ironlake_irq_handler [i915]] *ERROR* PCH transcoder A FIFO underrun
> 
> > > I reproduced with latest Linus master (@ 3e1e21c7b), and then
> > > bisected down to the following commit:
> > > 
> > > commit 7221fc333dbe1743a3dff155b03527fda90d4ec1
> > > Author: Matt Roper <matthew.d.roper at intel.com>
> > > Date:   Thu Sep 24 15:53:08 2015 -0700
> > > 
> > >     drm/i915: Eliminate usage of pipe_wm_parameters from ILK-style WM (v2)
> > 
> > That's not in 4.3.
> 
> Ah, you're right. I was going by the version in the Makefile at that commit,
> which says 4.3.0-rc3. git naiveté.
> 
> > As far as currentl Linus tree goes, you may want to try these:
> > http://patchwork.freedesktop.org/patch/msgid/1452776015-22076-2-git-send-email-ville.syrjala@linux.intel.com
> > http://patchwork.freedesktop.org/patch/msgid/1452776015-22076-1-git-send-email-ville.syrjala@linux.intel.com
> 
> Building - I'll test and report back.

fyi, the problem persists with 4.5-rc1 + these 2 patches.

  -dann