Re: [PATCH 3/3] drm/i915/display: Update calculation to avoid overflow

["Nautiyal, Ankit K" <ankit.k.nautiyal@xxxxxxxxx>]

On 6/12/2024 3:24 PM, Mitul Golani wrote:
> Update calculation to avoid overflow.
>
> Fixes: 1676ecd303ac ("drm/i915: Compute CMRR and calculate vtotal")
> Cc: Mitul Golani <mitulkumar.ajitkumar.golani@xxxxxxxxx>
> Cc: Ankit Nautiyal <ankit.k.nautiyal@xxxxxxxxx>
> Cc: Suraj Kandpal <suraj.kandpal@xxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
>
> Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@xxxxxxxxx>

Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@xxxxxxxxx>


> ---
>   drivers/gpu/drm/i915/display/intel_vrr.c | 9 +++++----
>   1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
> index dc9cf7ddafe9..5da9d5b9936e 100644
> --- a/drivers/gpu/drm/i915/display/intel_vrr.c
> +++ b/drivers/gpu/drm/i915/display/intel_vrr.c
> @@ -147,10 +147,11 @@ cmrr_get_vtotal(struct intel_crtc_state *crtc_state, bool video_mode_required)
>   		multiplier_n = 1000;
>   	}
>   
> -	crtc_state->cmrr.cmrr_n =
> -		desired_refresh_rate * adjusted_mode->crtc_htotal * multiplier_n;
> -	vtotal = (adjusted_mode->crtc_clock * 1000 * multiplier_n) / crtc_state->cmrr.cmrr_n;
> -	adjusted_pixel_rate = adjusted_mode->crtc_clock * 1000 * multiplier_m;
> +	crtc_state->cmrr.cmrr_n = mul_u32_u32(desired_refresh_rate * adjusted_mode->crtc_htotal,
> +					      multiplier_n);
> +	vtotal = DIV_ROUND_UP_ULL(mul_u32_u32(adjusted_mode->crtc_clock * 1000, multiplier_n),
> +				  crtc_state->cmrr.cmrr_n);
> +	adjusted_pixel_rate = mul_u32_u32(adjusted_mode->crtc_clock * 1000, multiplier_m);
>   	crtc_state->cmrr.cmrr_m = do_div(adjusted_pixel_rate, crtc_state->cmrr.cmrr_n);
>   
>   	return vtotal;