Re: [PATCH 4/9] drm/format-helper: Rework format-helper conversion functions

["Noralf Trønnes" <noralf@tronnes.org>]

Den 22.10.2021 15.28, skrev Thomas Zimmermann:
> Move destination-buffer clipping from all format-helper conversion
> functions into callers. Support destination-buffer pitch. Only
> distinguish between system and I/O memory, but use same logic
> everywhere.
> 
> Simply harmonize the interface and semantics of the existing code.
> Not all conversion helpers support all combinations of parameters.
> We have to add additional features when we need them.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---

>  /**
>   * drm_fb_xrgb8888_to_gray8 - Convert XRGB8888 to grayscale
>   * @dst: 8-bit grayscale destination buffer
> + * @dst_pitch: Number of bytes between two consecutive scanlines within dst
>   * @vaddr: XRGB8888 source buffer
>   * @fb: DRM framebuffer
>   * @clip: Clip rectangle area to copy
> @@ -415,16 +417,21 @@ EXPORT_SYMBOL(drm_fb_xrgb8888_to_rgb888_dstclip);
>   *
>   * ITU BT.601 is used for the RGB -> luma (brightness) conversion.
>   */
> -void drm_fb_xrgb8888_to_gray8(u8 *dst, void *vaddr, struct drm_framebuffer *fb,
> -			       struct drm_rect *clip)
> +void drm_fb_xrgb8888_to_gray8(void *dst, unsigned int dst_pitch, const void *vaddr,
> +			      const struct drm_framebuffer *fb, const struct drm_rect *clip)
>  {
>  	unsigned int len = (clip->x2 - clip->x1) * sizeof(u32);
>  	unsigned int x, y;
>  	void *buf;
> -	u32 *src;
> +	u8 *dst8;
> +	u32 *src32;
>  
>  	if (WARN_ON(fb->format->format != DRM_FORMAT_XRGB8888))
>  		return;
> +
> +	if (!dst_pitch)

len is source length (should really have been named src_len) which
results in a kernel crash:

> +		dst_pitch = len;

This works:

		dst_pitch = drm_rect_width(clip);

With that fixed:

Tested-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>

> +
>  	/*
>  	 * The cma memory is write-combined so reads are uncached.
>  	 * Speed up by fetching one line at a time.
> @@ -433,20 +440,22 @@ void drm_fb_xrgb8888_to_gray8(u8 *dst, void *vaddr, struct drm_framebuffer *fb,
>  	if (!buf)
>  		return;
>  
> +	vaddr += clip_offset(clip, fb->pitches[0], sizeof(u32));
>  	for (y = clip->y1; y < clip->y2; y++) {
> -		src = vaddr + (y * fb->pitches[0]);
> -		src += clip->x1;
> -		memcpy(buf, src, len);
> -		src = buf;
> +		dst8 = dst;
> +		src32 = memcpy(buf, vaddr, len);
>  		for (x = clip->x1; x < clip->x2; x++) {
> -			u8 r = (*src & 0x00ff0000) >> 16;
> -			u8 g = (*src & 0x0000ff00) >> 8;
> -			u8 b =  *src & 0x000000ff;
> +			u8 r = (*src32 & 0x00ff0000) >> 16;
> +			u8 g = (*src32 & 0x0000ff00) >> 8;
> +			u8 b =  *src32 & 0x000000ff;
>  
>  			/* ITU BT.601: Y = 0.299 R + 0.587 G + 0.114 B */
> -			*dst++ = (3 * r + 6 * g + b) / 10;
> -			src++;
> +			*dst8++ = (3 * r + 6 * g + b) / 10;
> +			src32++;
>  		}
> +
> +		vaddr += fb->pitches[0];
> +		dst += dst_pitch;
>  	}
>  
>  	kfree(buf);