linux-kernel - Re: [PATCH] drm/rect: remove useless call to clamp_t

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Date:   Wed, 20 Nov 2019 17:22:34 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Benjamin Gaignard <benjamin.gaignard@...com>
Cc:     maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        sean@...rly.run, airlied@...ux.ie, daniel@...ll.ch,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm/rect: remove useless call to clamp_t

On Tue, Nov 19, 2019 at 02:34:35PM +0100, Benjamin Gaignard wrote:
> Clamping a value between INT_MIN and INT_MAX always return the value itself
> and generate warnings when compiling with W=1.
> 
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...com>
> ---
>  drivers/gpu/drm/drm_rect.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_rect.c b/drivers/gpu/drm/drm_rect.c
> index b8363aaa9032..681f1fd09357 100644
> --- a/drivers/gpu/drm/drm_rect.c
> +++ b/drivers/gpu/drm/drm_rect.c
> @@ -89,7 +89,7 @@ bool drm_rect_clip_scaled(struct drm_rect *src, struct drm_rect *dst,
>  		u32 new_src_w = clip_scaled(drm_rect_width(src),
>  					    drm_rect_width(dst), diff);

Hmm. I think we borked this a bit when introducing clip_scaled().
'diff' can exceed dst width here so clip_scaled() should be able to
return a negative value.

Probably we should make this more consistent and do something like:
        diff = clip->x1 - dst->x1;
        if (diff > 0) {
-               u32 new_src_w = clip_scaled(drm_rect_width(src),
-                                           drm_rect_width(dst), diff);
+               int dst_w, new_src_w;

-               src->x1 = clamp_t(int64_t, src->x2 - new_src_w, INT_MIN, INT_MAX);
-               dst->x1 = clip->x1;
+               dst_w = drm_rect_width(dst);
+               diff = min(diff, dst_w);
+               new_src_w = clip_scaled(drm_rect_width(src), dst_w, diff);
+
+               src->x1 = src->x2 - new_src_w;
+               dst->x1 += diff;
        }

etc.

>  
> -		src->x1 = clamp_t(int64_t, src->x2 - new_src_w, INT_MIN, INT_MAX);
> +		src->x1 = src->x2 - new_src_w;
>  		dst->x1 = clip->x1;
>  	}
>  	diff = clip->y1 - dst->y1;
> @@ -97,7 +97,7 @@ bool drm_rect_clip_scaled(struct drm_rect *src, struct drm_rect *dst,
>  		u32 new_src_h = clip_scaled(drm_rect_height(src),
>  					    drm_rect_height(dst), diff);
>  
> -		src->y1 = clamp_t(int64_t, src->y2 - new_src_h, INT_MIN, INT_MAX);
> +		src->y1 = src->y2 - new_src_h;
>  		dst->y1 = clip->y1;
>  	}
>  	diff = dst->x2 - clip->x2;
> @@ -105,7 +105,7 @@ bool drm_rect_clip_scaled(struct drm_rect *src, struct drm_rect *dst,
>  		u32 new_src_w = clip_scaled(drm_rect_width(src),
>  					    drm_rect_width(dst), diff);
>  
> -		src->x2 = clamp_t(int64_t, src->x1 + new_src_w, INT_MIN, INT_MAX);
> +		src->x2 = src->x1 + new_src_w;
>  		dst->x2 = clip->x2;
>  	}
>  	diff = dst->y2 - clip->y2;
> @@ -113,7 +113,7 @@ bool drm_rect_clip_scaled(struct drm_rect *src, struct drm_rect *dst,
>  		u32 new_src_h = clip_scaled(drm_rect_height(src),
>  					    drm_rect_height(dst), diff);
>  
> -		src->y2 = clamp_t(int64_t, src->y1 + new_src_h, INT_MIN, INT_MAX);
> +		src->y2 = src->y1 + new_src_h;
>  		dst->y2 = clip->y2;
>  	}
>  
> -- 
> 2.15.0
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Ville Syrjälä
Intel

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