[Intel-gfx] [PATCH v2] drm/i915/display: assume some pixelrate for src smaller than 1

[Imre Deak]

On Sun, Jan 08, 2023 at 01:30:44PM +0200, Juha-Pekka Heikkila wrote:
> intel_adjusted_rate() didn't take into account src rectangle
> can be less than 1 in with or height.

Thanks for catching this.

> Signed-off-by: Juha-Pekka Heikkila <juhapekka.heikkila at gmail.com>
> ---
>  drivers/gpu/drm/i915/display/intel_atomic_plane.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_atomic_plane.c b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> index 10e1fc9d0698..cd24d069b6eb 100644
> --- a/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> +++ b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> @@ -144,7 +144,7 @@ unsigned int intel_adjusted_rate(const struct drm_rect *src,
>  				 const struct drm_rect *dst,
>  				 unsigned int rate)
>  {
> -	unsigned int src_w, src_h, dst_w, dst_h;
> +	unsigned int src_w, src_h, dst_w, dst_h, dst_wh;
>  
>  	src_w = drm_rect_width(src) >> 16;
>  	src_h = drm_rect_height(src) >> 16;
> @@ -155,8 +155,10 @@ unsigned int intel_adjusted_rate(const struct drm_rect *src,
>  	dst_w = min(src_w, dst_w);
>  	dst_h = min(src_h, dst_h);
>  
> -	return DIV_ROUND_UP_ULL(mul_u32_u32(rate, src_w * src_h),
> -				dst_w * dst_h);
> +	/* in case src contained only fractional part */
> +	dst_wh = max(dst_w * dst_h, 1U);
> +
> +	return DIV_ROUND_UP_ULL(mul_u32_u32(rate, src_w * src_h), dst_wh);

The div-by-zero is avoided, but we'd return a 0 rate which doesn't look
ok to me. I'd round up instead of down when converting src_w/h from
fixed point to int above.

>  }
>  
>  unsigned int intel_plane_pixel_rate(const struct intel_crtc_state *crtc_state,
> -- 
> 2.39.0
>