[Intel-gfx] [3.14.0-rc4] regression: drm FIFO underruns

[Daniel Vetter]

On Sat, May 10, 2014 at 10:52 AM, Jörg Otte <jrg.otte at gmail.com> wrote:
>> On Fri, May 09, 2014 at 05:14:38PM +0100, Damien Lespiau wrote:
>>> On Fri, May 09, 2014 at 06:11:37PM +0200, Jörg Otte wrote:
>>> > > Jörg, can you please boot with drm.debug=0xe, reproduce the issue and
>>> > > then attach the complete dmesg? Please make sure that the dmesg
>>> > > contains the boot-up stuff too.
>>> > >
>>> > > Thanks, Daniel
>>> > Here it is. I should mention it only happens at boot-up.
>>>
>>> [    0.374095] [drm] Wrong MCH_SSKPD value: 0x20100406
>>> [    0.374096] [drm] This can cause pipe underruns and display issues.
>>> [    0.374097] [drm] Please upgrade your BIOS to fix this.
>>
>> That can be a factor, but I think we may have some more general issue
>> in the modeset sequence which causes these to get reported. I'm getting
>> some on my machine as well where SSKPD looks more sane. Maybe we turn on
>> the error reporting too early or something.
>>
>> But I'm not going to spend time worrying about these before my previous
>> watermark stuff gets merged. Also the underrun reporting code itself
>> would need some kind of rewrite to be really useful.
>>
>> If the display doesn't blank out during use everything is more or less
>> fine and you can ignore these errors. It's quite likely that the
>> errors were always present and you didn't know it. We just made them
>> more prominent recently.
>>
>> --
>> Ville Syrjälä
>> Intel OTC
>
> It comes out on the boot-up screen which is normally clean. So it becomes
> highly visible for anyone.

To make sure that you're only seeing this at boot up and not elseplace
please check that it doesn't show up when you do anything of the
below:
a) suspend/resume
b) changing the output mode (e.g. with xrandr --mode)
c) changing the output pipe (e.g. with xrandr --crtc)
d) all of the above but with heavy system load, e.g. compile kernels
with make -j <num-cores*2>

Also please test the latest drm-intel-nightly branch from
http://cgit.freedesktop.org/drm-intel to make sure we haven't yet
fixed this in our -next branch.

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch