[0/2] fbdev: Fix image blitting for arbitrary image widths

Recent optimization of the fbdev image-bitting helpers broke the code for
image width that do not align with multiples of 8. Both, sys and cfb, are
affected. Fix this problem by handling the trailing pixels on each line
separately.

Tested with simpledrm and the 7x14 font.

Thomas Zimmermann (2):
  fbdev: Fix sys_imageblit() for arbitrary image widths
  fbdev: Fix cfb_imageblit() for arbitrary image widths

 drivers/video/fbdev/core/cfbimgblt.c | 28 +++++++++++++++++++++++----
 drivers/video/fbdev/core/sysimgblt.c | 29 ++++++++++++++++++++++++----
 2 files changed, 49 insertions(+), 8 deletions(-)

On 13.03.2022 20:29, Thomas Zimmermann wrote:
> Commit 0d03011894d2 ("fbdev: Improve performance of cfb_imageblit()")
> broke cfb_imageblit() for image widths that are not aligned to 8-bit
> boundaries. Fix this by handling the trailing pixels on each line
> separately. The performance improvements in the original commit do not
> regress by this change.
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Fixes: 0d03011894d2 ("fbdev: Improve performance of cfb_imageblit()")
> Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Javier Martinez Canillas <javierm@redhat.com>
> Cc: Sam Ravnborg <sam@ravnborg.org>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
>   drivers/video/fbdev/core/cfbimgblt.c | 28 ++++++++++++++++++++++++----
>   1 file changed, 24 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/video/fbdev/core/cfbimgblt.c b/drivers/video/fbdev/core/cfbimgblt.c
> index 7361cfabdd85..9ebda4e0dc7a 100644
> --- a/drivers/video/fbdev/core/cfbimgblt.c
> +++ b/drivers/video/fbdev/core/cfbimgblt.c
> @@ -218,7 +218,7 @@ static inline void fast_imageblit(const struct fb_image *image, struct fb_info *
>   {
>   	u32 fgx = fgcolor, bgx = bgcolor, bpp = p->var.bits_per_pixel;
>   	u32 ppw = 32/bpp, spitch = (image->width + 7)/8;
> -	u32 bit_mask, eorx;
> +	u32 bit_mask, eorx, shift;
>   	const char *s = image->data, *src;
>   	u32 __iomem *dst;
>   	const u32 *tab = NULL;
> @@ -259,17 +259,23 @@ static inline void fast_imageblit(const struct fb_image *image, struct fb_info *
>   
>   	for (i = image->height; i--; ) {
>   		dst = (u32 __iomem *)dst1;
> +		shift = 8;
>   		src = s;
>   
> +		/*
> +		 * Manually unroll the per-line copying loop for better
> +		 * performance. This works until we processed the last
> +		 * completely filled source byte (inclusive).
> +		 */
>   		switch (ppw) {
>   		case 4: /* 8 bpp */
> -			for (j = k; j; j -= 2, ++src) {
> +			for (j = k; j >= 2; j -= 2, ++src) {
>   				FB_WRITEL(colortab[(*src >> 4) & bit_mask], dst++);
>   				FB_WRITEL(colortab[(*src >> 0) & bit_mask], dst++);
>   			}
>   			break;
>   		case 2: /* 16 bpp */
> -			for (j = k; j; j -= 4, ++src) {
> +			for (j = k; j >= 4; j -= 4, ++src) {
>   				FB_WRITEL(colortab[(*src >> 6) & bit_mask], dst++);
>   				FB_WRITEL(colortab[(*src >> 4) & bit_mask], dst++);
>   				FB_WRITEL(colortab[(*src >> 2) & bit_mask], dst++);
> @@ -277,7 +283,7 @@ static inline void fast_imageblit(const struct fb_image *image, struct fb_info *
>   			}
>   			break;
>   		case 1: /* 32 bpp */
> -			for (j = k; j; j -= 8, ++src) {
> +			for (j = k; j >= 8; j -= 8, ++src) {
>   				FB_WRITEL(colortab[(*src >> 7) & bit_mask], dst++);
>   				FB_WRITEL(colortab[(*src >> 6) & bit_mask], dst++);
>   				FB_WRITEL(colortab[(*src >> 5) & bit_mask], dst++);
> @@ -290,6 +296,20 @@ static inline void fast_imageblit(const struct fb_image *image, struct fb_info *
>   			break;
>   		}
>   
> +		/*
> +		 * For image widths that are not a multiple of 8, there
> +		 * are trailing pixels left on the current line. Print
> +		 * them as well.
> +		 */
> +		for (; j--; ) {
> +			shift -= ppw;
> +			FB_WRITEL(colortab[(*src >> shift) & bit_mask], dst++);
> +			if (!shift) {
> +				shift = 8;
> +				++src;
> +			}
> +		}
> +
>   		dst1 += p->fix.line_length;
>   		s += spitch;
>   	}

Best regards