Re: [PATCH] drm/i915: Avoid divide by zero

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

On Wed, Jan 23, 2019 at 07:21:57AM +0000, Kahola, Mika wrote:
> On Tue, 2019-01-22 at 21:09 +0200, Ville Syrjälä wrote:
> > On Tue, Jan 22, 2019 at 08:09:40PM +0200, Jani Nikula wrote:
> > > On Tue, 22 Jan 2019, Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > wrote:
> > > > On Tue, Jan 22, 2019 at 02:58:24PM +0200, Mika Kahola wrote:
> > > > > Avoid divide by zero warning on static analysis.
> > > > > 
> > > > > Signed-off-by: Mika Kahola <mika.kahola@intel.com>
> > > > > ---
> > > > >  drivers/gpu/drm/i915/intel_pm.c | 6 ++++--
> > > > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/i915/intel_pm.c
> > > > > b/drivers/gpu/drm/i915/intel_pm.c
> > > > > index 8b63afa3a221..6a8e8b3f44c2 100644
> > > > > --- a/drivers/gpu/drm/i915/intel_pm.c
> > > > > +++ b/drivers/gpu/drm/i915/intel_pm.c
> > > > > @@ -3912,8 +3912,10 @@
> > > > > skl_ddb_get_pipe_allocation_limits(struct drm_i915_private
> > > > > *dev_priv,
> > > > >  			pipe_width = hdisplay;
> > > > >  	}
> > > > >  
> > > > > -	alloc->start = ddb_size * width_before_pipe /
> > > > > total_width;
> > > > > -	alloc->end = ddb_size * (width_before_pipe +
> > > > > pipe_width) / total_width;
> > > > > +	alloc->start = total_width == 0 ?
> > > > > +		0 : ddb_size * width_before_pipe / total_width;
> > > > > +	alloc->end = total_width == 0 ?
> > > > > +		0 : ddb_size * (width_before_pipe + pipe_width)
> > > > > / total_width;
> > > > 
> > > > Can't happen.
> I'd say it's very unlikely to happen but in theory possible. If we
> don't have any crtc_state enabled we end up having total_width = 0. In
> this case it probably won't matter what numbers we end up with alloc-
> >start and alloc->end.

The caller bails out early in that case:

if (!cstate->base.active) {
	alloc->start = alloc->end = 0;
	return 0;
}

> 
> Anyway, this was something that caught my eye while looking into crc
> mismatch errors and static checker results.
> 
> Like Jani said, warn is sufficient with this case.
> 
> Cheers,
> Mika
> 
> > > 
> > > Yeah, it's about stfu the checker...
> > 
> > Feels like the tip of an iceberg. How many more uglies are we going
> > to
> > have to add?
> > 
> > > 
> > > > 
> > > > >  }
> > > > >  
> > > > >  static unsigned int skl_cursor_allocation(int num_active)
> > > > > -- 
> > > > > 2.17.1
> > > > > 
> > > > > _______________________________________________
> > > > > Intel-gfx mailing list
> > > > > Intel-gfx@lists.freedesktop.org
> > > > > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> > > 
> > > -- 
> > > Jani Nikula, Intel Open Source Graphics Center
> > 
> > 

-- 
Ville Syrjälä
Intel
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