[Intel-gfx] [PATCH] drm/i915: Avoid divide by zero

[Kahola, Mika]

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 at 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 at 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.

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 at lists.freedesktop.org
> > > > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> > 
> > -- 
> > Jani Nikula, Intel Open Source Graphics Center
> 
>