Re: [PATCH 01/17] drm/i915: Clear pipestat consistently

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Jun 22, 2017 at 01:39:47PM +0100, Chris Wilson wrote:
> Quoting ville.syrjala@linux.intel.com (2017-06-22 12:55:39)
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > We have a lot of different ways of clearing the PIPESTAT registers.
> > Let's unify it all into one function. There's no magic in PIPESTAT
> > that would require any of the double clearing and whatnot that
> > some of the code tries to do. All we can really do is clear the status
> > bits and disable the enable bits. There is no way to mask anything
> > so as soon as another event happens the status bit will become set
> > again, and trying to clear them twice or something can't protect
> > against that.
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_irq.c | 67 ++++++++++++++++++-----------------------
> >  1 file changed, 30 insertions(+), 37 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> > index b1c7d1a04612..6daaf47482d4 100644
> > --- a/drivers/gpu/drm/i915/i915_irq.c
> > +++ b/drivers/gpu/drm/i915/i915_irq.c
> > @@ -1732,6 +1732,19 @@ static bool intel_pipe_handle_vblank(struct drm_i915_private *dev_priv,
> >         return ret;
> >  }
> >  
> > +static void i9xx_pipestat_irq_reset(struct drm_i915_private *dev_priv)
> > +{
> > +       enum pipe pipe;
> > +
> > +       for_each_pipe(dev_priv, pipe) {
> > +               I915_WRITE(PIPESTAT(pipe),
> > +                          PIPESTAT_INT_STATUS_MASK |
> > +                          PIPE_FIFO_UNDERRUN_STATUS);
> 
> Hmm, is this change for i915/i965 significant? Maybe explain it away in
> the changelog?

Sorry missed your question. Which change are we concerned about here
specifically?

As the commit message tried to explain, the "first disable then clear"
thing at least is pointless, and we can just do it in one step.
But maybe that wasn't the part you're thinking about?

-- 
Ville Syrjälä
Intel OTC
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