Re: [Intel-gfx] [PATCH v2 4/8] drm/i915: Reject excessive SAGV block time

["Lisovskiy, Stanislav" <stanislav.lisovskiy@intel.com>]

On Wed, Mar 09, 2022 at 06:49:44PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> If the mailbox returns an exceesively large SAGV block time let's just
> reject it. This avoids having to worry about overflows when we add the
> SAGV block time to the wm0 latency.
> 
> We shall put the limit arbitrarily at U16_MAX. >65msec latency
> doesn't really make sense to me in any case.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>

> ---
>  drivers/gpu/drm/i915/intel_pm.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 36f5bccabf64..166246fa27e4 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -3716,6 +3716,12 @@ static void intel_sagv_init(struct drm_i915_private *i915)
>  	drm_dbg_kms(&i915->drm, "SAGV supported: %s, original SAGV block time: %u us\n",
>  		    str_yes_no(intel_has_sagv(i915)), i915->sagv_block_time_us);
>  
> +	/* avoid overflow when adding with wm0 latency/etc. */
> +	if (drm_WARN(&i915->drm, i915->sagv_block_time_us > U16_MAX,
> +		     "Excessive SAGV block time %u, ignoring\n",
> +		     i915->sagv_block_time_us))
> +		i915->sagv_block_time_us = 0;
> +
>  	if (!intel_has_sagv(i915))
>  		i915->sagv_block_time_us = 0;
>  }
> -- 
> 2.34.1
>