fbdev: Fix sys_imageblit() for arbitrary image widths

Commit 6f29e04938bf ("fbdev: Improve performance of sys_imageblit()")
broke sys_imageblit() for image width 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: 6f29e04938bf ("fbdev: Improve performance of sys_imageblit()")
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220313192952.12058-2-tzimmermann@suse.de

diff --git a/drivers/video/fbdev/core/sysimgblt.c b/drivers/video/fbdev/core/sysimgblt.c
index 722c327..335e92b 100644 (file)
--- a/drivers/video/fbdev/core/sysimgblt.c
+++ b/drivers/video/fbdev/core/sysimgblt.c
@@ -188,7 +188,7 @@ static void fast_imageblit(const struct fb_image *image, struct fb_info *p,
 {
        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 *dst;
        const u32 *tab;
@@ -229,17 +229,23 @@ static void fast_imageblit(const struct fb_image *image, struct fb_info *p,
 
        for (i = image->height; i--; ) {
                dst = 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) {
                                *dst++ = colortab[(*src >> 4) & bit_mask];
                                *dst++ = colortab[(*src >> 0) & bit_mask];
                        }
                        break;
                case 2: /* 16 bpp */
-                       for (j = k; j; j -= 4, ++src) {
+                       for (j = k; j >= 4; j -= 4, ++src) {
                                *dst++ = colortab[(*src >> 6) & bit_mask];
                                *dst++ = colortab[(*src >> 4) & bit_mask];
                                *dst++ = colortab[(*src >> 2) & bit_mask];
@@ -247,7 +253,7 @@ static void fast_imageblit(const struct fb_image *image, struct fb_info *p,
                        }
                        break;
                case 1: /* 32 bpp */
-                       for (j = k; j; j -= 8, ++src) {
+                       for (j = k; j >= 8; j -= 8, ++src) {
                                *dst++ = colortab[(*src >> 7) & bit_mask];
                                *dst++ = colortab[(*src >> 6) & bit_mask];
                                *dst++ = colortab[(*src >> 5) & bit_mask];
@@ -259,6 +265,21 @@ static void fast_imageblit(const struct fb_image *image, struct fb_info *p,
                        }
                        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;
+                       *dst++ = colortab[(*src >> shift) & bit_mask];
+                       if (!shift) {
+                               shift = 8;
+                               ++src;
+                       }
+               }
+
                dst1 += p->fix.line_length;
                s += spitch;
        }