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

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Date:	Sat, 10 May 2014 10:52:30 +0200
From:	Jörg Otte <jrg.otte@...il.com>
To:	Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:	Damien Lespiau <damien.lespiau@...el.com>,
	David Airlie <airlied@...ux.ie>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	intel-gfx <intel-gfx@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Airlie <airlied@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [Intel-gfx] [3.14.0-rc4] regression: drm FIFO underruns

2014-05-09 19:03 GMT+02:00 Ville Syrjälä <ville.syrjala@...ux.intel.com>:
> 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.

Thanks, Jörg
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