[Intel-gfx] [PATCH] drm/i915/display: Warn if the FBC is still writing to stolen on removal

[Chris Wilson]

Quoting Ville Syrjälä (2020-05-04 14:49:28)
> On Sun, May 03, 2020 at 07:00:34PM +0100, Chris Wilson wrote:
> > If the FBC is still writing into stolen, it will overwrite any future
> > users of that stolen region. Check before release.
> > 
> > References: https://gitlab.freedesktop.org/drm/intel/-/issues/1635
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > ---
> >  drivers/gpu/drm/i915/display/intel_fbc.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_fbc.c b/drivers/gpu/drm/i915/display/intel_fbc.c
> > index c6afa10e814c..37244ed92ae4 100644
> > --- a/drivers/gpu/drm/i915/display/intel_fbc.c
> > +++ b/drivers/gpu/drm/i915/display/intel_fbc.c
> > @@ -540,6 +540,9 @@ static void __intel_fbc_cleanup_cfb(struct drm_i915_private *dev_priv)
> >  {
> >       struct intel_fbc *fbc = &dev_priv->fbc;
> >  
> > +     if (WARN_ON(intel_fbc_hw_is_active(dev_priv)))
> > +             return;
> > +
> 
> Can't immediately see how that would hapoen, but no harm in checking.

I'm clutching at straws to explain how come fi-bxt-dsi is overwriting

<7> [592.789844] heartbeat [0000] f0101011 f12ff12f f12ff12f f12ff12f f12ff12f f12ff12f f12ff12f f12ff12f
<7> [592.789853] heartbeat [0020] f12ff12f f12ff12f f12ff12f f12ff12f f12ff12f f12ff12f f12ff12f f12ff12f
<7> [592.789860] heartbeat *
<7> [592.789869] heartbeat [0060] f12ff12f f12ff12f f12ff12f f12ff12f c12ff12f f100000f f12ff12f f12ff12f

into sensitive locations. My theory is that it is stolen memory being
clobbers with what looks like some odd pixel data. FBC being a suspect,
hence getting something like this check in place for the idle runs and
see what turns up.
-Chris