Re: Possible i915 regression with 4.4-rc

From: Dave Gordon <david.s.gordon@intel.com>
To: "Chris Wilson" <chris@chris-wilson.co.uk>,
	"Ville Syrjälä" <ville.syrjala@linux.intel.com>,
	"Takashi Iwai" <tiwai@suse.de>,
	intel-gfx@lists.freedesktop.org
Subject: Re: Possible i915 regression with 4.4-rc
Date: Fri, 4 Dec 2015 12:00:08 +0000	[thread overview]
Message-ID: <56618048.1080206@intel.com> (raw)
In-Reply-To: <20151203213559.GA29847@nuc-i3427.alporthouse.com>

On 03/12/15 21:35, Chris Wilson wrote:
> On Thu, Dec 03, 2015 at 11:25:48PM +0200, Ville Syrjälä wrote:
>> On Thu, Dec 03, 2015 at 10:08:05PM +0100, Takashi Iwai wrote:
>>> On Thu, 03 Dec 2015 21:33:29 +0100,
>>> Ville Syrjälä wrote:
>>>>
>>>> On Thu, Dec 03, 2015 at 09:00:55PM +0100, Takashi Iwai wrote:
>>>>> Hi,
>>>>>
>>>>> I've experienced a few graphics issues recently, and I tend to believe
>>>>> that it has happened since 4.4-rc.  Namely, after some long time usage
>>>>> on my HSW laptop (two or three days), the mouse cursor vanished
>>>>> suddenly.  It kept pointing but just became invisible.  Also, after
>>>>> some S3 cycles, some glyphs on a console or on Firefox became
>>>>> invisible, too.  The windows and graphics were shown well, and X core
>>>>> fonts were still shown properly, too.  Switching to VT1 and back
>>>>> didn't change the situation.
>>>>
>>>> I think I have a fix for this *very* annoying problem. I'v been cursing
>>>> on irc for weeks about it, until I finally got off my arse and debugged
>>>> it.
>>>>
>>>> I pushed out my my cursor branch:
>>>> git://github.com/vsyrjala/linux.git disappearing_cursor_fix
>>>>
>>>> It has lots of other junk too, but it should be just there two that fix it:
>>>> 59f65fa270fb ("drm/i915: Kill intel_crtc->cursor_bo")
>>>> 25651a198d17 ("drm/i915: Drop the broken curcor base==0 special casing")
>>>>
>>>> Unfortunatleey I've managed to keep myself busy on other stuff, so didn't
>>>> send them out yet. Maybe tomorrow...
>>>
>>> Great, I'll try them out now.  But these look like fixing only the
>>> cursor issue.  Would they cover also the missing glyphs I experienced?
>>
>> No. That's either userland, or some object/context/etc. getting corrupted
>> I think. I've had something like that occasionally too after some number of
>> suspend cycles, and usually fbcon is dead at that point too (just get a
>> black screen on VT switch).
>>
>> I think we had some bug with not properly pinning the fbdev buffer which
>> could explain things getting corrupted. Chris had a fix I think, but I'm
>> not sure if that went anywhere. Chris?
>
> Jani keeps refusing it :). But it's not the issue with the missing
> glyphs. The missing glyphs is the kernel dropping rendering, or that
> rendering not being flushed out to memory across the suspend as it is just
> texture corruption. The glyph cache only slowly changes, so corruption
> tends to be visible for some time.  An alternative explanation would be
> that GPU state is not restored upon resume that only (visibly) effects
> glyph rendering (and portions thereof). Lost rendering is a simpler
> explanation.
> -Chris

Could also be down to certain objects getting their contents discarded 
when evicted (due to not being marked dirty), for which I posted a fix 
"Always mark GEM objects as dirty when written by the CPU" a few days ago?

.Dave.
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