[Intel-gfx] [PATCH 2/2] drm/i915: avoid division by zero on cnl_calc_wrpll_link

[Rodrigo Vivi]

On Thu, Oct 05, 2017 at 09:38:42PM +0000, Paulo Zanoni wrote:
> If for some unexpected reason the registers all read zero it's better
> to WARN and return instead of dividing by zero and completely freezing
> the machine.
> 
> I don't expect this to happen in the wild with the current code, but I
> accidentally triggered the division by zero while doing some debugging
> in an unusual environment.

Good idea

Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>

> 
> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_ddi.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index f7c91bb..be86eb6 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -1220,6 +1220,9 @@ static int cnl_calc_wrpll_link(struct drm_i915_private *dev_priv,
>  	dco_freq += (((cfgcr0 & DPLL_CFGCR0_DCO_FRACTION_MASK) >>
>  		      DPLL_CFGCR0_DCO_FRACTION_SHIFT) * ref_clock) / 0x8000;
>  
> +	if (WARN_ON(p0 == 0 || p1 == 0 || p2 == 0))
> +		return 0;
> +
>  	return dco_freq / (p0 * p1 * p2 * 5);
>  }
>  
> -- 
> 2.9.5
>