Re: [PATCH 08/15] drm/i915/pfit: Unconfuse panel_fitter_scaling()

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 19 Oct 2026, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> panel_fitter_scaling() apparently tries to implemnt

*implement

> DIV_ROUND_CLOSEST() by hand, but in a somewhat weird way
> where the division and rounding are done as separate steps.
> Just use the real DIV_ROUND_CLOSEST() instead.
>
> This does in fact match how the i965+ hardware calculates
> the automagic scaling factors, which will be important
> for upcoming readout support.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_pfit.c | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_pfit.c b/drivers/gpu/drm/i915/display/intel_pfit.c
> index 82804159d0a1..5d519f45adbe 100644
> --- a/drivers/gpu/drm/i915/display/intel_pfit.c
> +++ b/drivers/gpu/drm/i915/display/intel_pfit.c
> @@ -350,15 +350,7 @@ centre_vertically(struct drm_display_mode *adjusted_mode,
>  
>  static u32 panel_fitter_scaling(u32 source, u32 target)
>  {
> -	/*
> -	 * Floating point operation is not supported. So the FACTOR
> -	 * is defined, which can avoid the floating point computation
> -	 * when calculating the panel ratio.
> -	 */
> -#define ACCURACY 12
> -#define FACTOR (1 << ACCURACY)
> -	u32 ratio = source * FACTOR / target;
> -	return (FACTOR * ratio + FACTOR/2) / FACTOR;
> +	return DIV_ROUND_CLOSEST(source << 12, target);
>  }
>  
>  static void i965_scale_aspect(struct intel_crtc_state *crtc_state,

-- 
Jani Nikula, Intel