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, 9 insertions, 0 deletions

diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index f1cc8996456f..5c1ef0938006 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig
@@ -103,6 +103,15 @@ config FB_CFB_IMAGEBLIT
 	  blitting. This is used by drivers that don't provide their own
 	  (accelerated) version.
 
+config FB_CFB_REV_PIXELS_IN_BYTE
+	bool
+	depends on FB
+	default n
+	---help---
+	  Allow generic frame-buffer functions to work on displays with 1, 2
+	  and 4 bits per pixel depths which has opposite order of pixels in
+	  byte order to bytes in long order.
+
 config FB_SYS_FILLRECT
 	tristate
 	depends on FB