fbdev: Support for byte-reversed framebuffer formats

Allow generic frame-buffer code to correctly write texts and blit images for
1, 2 and 4 bit per pixel frame-buffer organizations when pixels in bytes are
organized to in opposite order than bytes in long type.

Overhead should be reasonable.  If option is not selected, than compiler
should eliminate completely all overhead.

The feature is disabled at compile time if CONFIG_FB_CFB_REV_PIXELS_IN_BYTE is
not set.

[adaplas]
Convert helper functions to macros if feature is not enabled.

Signed-off-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>
Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 68 insertions, 0 deletions

diff --git a/drivers/video/fb_draw.h b/drivers/video/fb_draw.h
index c5c45203833b..816843f06bb7 100644
--- a/drivers/video/fb_draw.h
+++ b/drivers/video/fb_draw.h
@@ -2,6 +2,7 @@
 #define _FB_DRAW_H
 
 #include <asm/types.h>
+#include <linux/fb.h>
 
     /*
      *  Compose two values, using a bitmask as decision value
@@ -69,4 +70,71 @@ pixel_to_pat( u32 bpp, u32 pixel)
     }
 }
 #endif
+
+#ifdef CONFIG_FB_CFB_REV_PIXELS_IN_BYTE
+
+static inline u32 fb_shifted_pixels_mask_u32(u32 index, u32 bswapmask)
+{
+        u32 mask;
+
+        if (!bswapmask) {
+                mask = FB_SHIFT_HIGH(~(u32)0, index);
+        } else {
+                mask = 0xff << FB_LEFT_POS(8);
+                mask = FB_SHIFT_LOW(mask, index & (bswapmask)) & mask;
+                mask = FB_SHIFT_HIGH(mask, index & ~(bswapmask));
+#if defined(__i386__) || defined(__x86_64__)
+                /* Shift argument is limited to 0 - 31 on x86 based CPU's */
+                if(index + bswapmask < 32)
+#endif
+                        mask |= FB_SHIFT_HIGH(~(u32)0,
+                                        (index + bswapmask) & ~(bswapmask));
+        }
+        return mask;
+}
+
+static inline unsigned long fb_shifted_pixels_mask_long(u32 index, u32 bswapmask)
+{
+        unsigned long mask;
+
+        if (!bswapmask) {
+                mask = FB_SHIFT_HIGH(~0UL, index);
+        } else {
+                mask = 0xff << FB_LEFT_POS(8);
+                mask = FB_SHIFT_LOW(mask, index & (bswapmask)) & mask;
+                mask = FB_SHIFT_HIGH(mask, index & ~(bswapmask));
+#if defined(__i386__) || defined(__x86_64__)
+                /* Shift argument is limited to 0 - 31 on x86 based CPU's */
+                if(index + bswapmask < BITS_PER_LONG)
+#endif
+                        mask |= FB_SHIFT_HIGH(~0UL,
+                                        (index + bswapmask) & ~(bswapmask));
+        }
+        return mask;
+}
+
+
+static inline u32 fb_compute_bswapmask(struct fb_info *info)
+{
+        u32 bswapmask = 0;
+        unsigned bpp = info->var.bits_per_pixel;
+
+        if ((bpp < 8) && (info->var.nonstd & FB_NONSTD_REV_PIX_IN_B)) {
+                /*
+                 * Reversed order of pixel layout in bytes
+                 * works only for 1, 2 and 4 bpp
+                 */
+                bswapmask = 7 - bpp + 1;
+        }
+        return bswapmask;
+}
+
+#else /* CONFIG_FB_CFB_REV_PIXELS_IN_BYTE */
+
+#define fb_shifted_pixels_mask_u32(i, b) FB_SHIFT_HIGH(~(u32)0, (i))
+#define fb_shifted_pixels_mask_long(i, b) FB_SHIFT_HIGH(~0UL, (i))
+#define fb_compute_bswapmask(...) 0
+
+#endif  /* CONFIG_FB_CFB_REV_PIXELS_IN_BYTE */
+
 #endif /* FB_DRAW_H */