[Intel-gfx] [PATCH] drm/i915: Don't write DSPSURF for old chips

[Chris Wilson]

On Tue, 28 Feb 2012 07:43:55 +0100, Takashi Iwai <tiwai at suse.de> wrote:
> At Mon, 27 Feb 2012 14:08:28 +0100,
> Takashi Iwai wrote:
> > 
> > At Mon, 27 Feb 2012 12:17:57 +0000,
> > Chris Wilson wrote:
> > > 
> > > On Mon, 27 Feb 2012 12:39:24 +0100, Takashi Iwai <tiwai at suse.de> wrote:
> > > > It seems that writing DSPSURF in intel_flush_display_plane() causes
> > > > the blank screen on some old laptops like Dell D630 with 965GM.
> > > > Since this operation is needed only for ILK+, make it conditional.
> > > 
> > > The specs say that DSPASURF is the latch register for updates of the DSPA
> > > registers on gen4 (including 965gm) as well. Presumably the bug is that
> > > we only partially update the DSPA registers prior to the first call to
> > > intel_flush_display_plane() which this papers over by disabling the
> > > update until a valid address is written to DSPASURF. And there is such a
> > > spurious call to intel_enable_plane() prior to us setting a valid
> > > scanout surface:
> > 
> > Sounds reasonable.  FWIW, the change was first introduced in commit
> > [b24e7179: drm/i915: add pipe/plane enable/disable functions],
> > then in commit [efc2924e: drm/i915: Call intel_enable_plane from
> > i9xx_crtc_mode_set (again)], it's placed into i9xx_crtc_mode_set().
> > 
> > This explains the fact that it was discovered only on old machines
> > as i9xx_crtc_mode_set() is the only crtc_mode_set op calling
> > intel_enable_plane().
> > 
> > BTW, the bisection leaded to a merge commit, so the bug is really
> > depending on the activation path or timing.
> > 
> > I'll ask a tester to try your patch.
> 
> He reported back that it reduces the failure rate but doesn't fix
> completely.  Still get a blank screen in 20% rate.
> 
> Any other clue?

I haven't yet found anything else in the same vein as this, but the
965gm does ring a warning bell for this recent regression:

commit 5ca0c34ae28344b6b4ca3036bc82f89c8db16a59
Author: Dave Airlie <airlied at redhat.com>
Date:   Thu Feb 23 15:33:40 2012 +0000

    drm/i915: fix mode set on load pipe. (v2)
    
    Booted my i965 machine and it started printing the unsupported pixel
    format of 0 message (once I added content to it).
    
    Oh looksie here, we pass 0. fix.
    
    v2: compile it.
    
    Buzilla: https://bugs.freedesktop.org/show_bug.cgi?id=45966
    
    Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
    Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
    Signed-off-by: Dave Airlie <airlied at redhat.com>
    Signed-off-by: Jesse Barnes <jbarnes at virtuousgeek.org>

which is currently sitting in airlied/drm-fixes.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre