[Intel-gfx] Possible i915 regression with 4.4-rc

[Chris Wilson]

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

-- 
Chris Wilson, Intel Open Source Technology Centre