[Intel-gfx] [PATCH] drm/i915: Double check we didn't miss an unclaimed register access

[Chris Wilson]

Quoting Chris Wilson (2018-09-04 13:38:27)
> Quoting Mika Kuoppala (2018-09-04 13:34:12)
> > Chris Wilson <chris at chris-wilson.co.uk> writes:
> > 
> > > Currently, if the user has enabled mmio-debug around each register
> > > access, we presume that we have then checked them all. However, it is
> > > still possible through omission (raw register access) or external
> > > interaction that the unclaimed access was not highlighted.
> > >
> > > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > > Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/intel_uncore.c | 13 +++++++------
> > >  1 file changed, 7 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> > > index 20f2f5ad9c3f..05f0cda18501 100644
> > > --- a/drivers/gpu/drm/i915/intel_uncore.c
> > > +++ b/drivers/gpu/drm/i915/intel_uncore.c
> > > @@ -2283,15 +2283,16 @@ bool intel_uncore_unclaimed_mmio(struct drm_i915_private *dev_priv)
> > >  bool
> > >  intel_uncore_arm_unclaimed_mmio_detection(struct drm_i915_private *dev_priv)
> > >  {
> > > -     if (unlikely(i915_modparams.mmio_debug ||
> > > -                  dev_priv->uncore.unclaimed_mmio_check <= 0))
> > > +     if (unlikely(dev_priv->uncore.unclaimed_mmio_check <= 0))
> > >               return false;
> > >
> > 
> > We could catch the readers attention by marking this as READ_ONCE.
> > 
> > 
> > And then take spinlock here before checking for unclaimed.
> 
> Could do, feels like overkill, but not contentious.

Implied here, is improving unclaimed_mmio_check a fundamental
requirement for this patch or additional work? I think the latter.
-Chris