fbdev/efifb: Fix 16 color palette entry calculation

commit d50b3f43db739f03fcf8c0a00664b3d2fed0496e upstream.

When using efifb with a 16-bit (5:6:5) visual, fbcon's text is rendered
in the wrong colors - e.g. text gray (#aaaaaa) is rendered as green
(#50bc50) and neighboring pixels have slightly different values
(such as #50bc78).

The reason is that fbcon loads its 16 color palette through
efifb_setcolreg(), which in turn calculates a 32-bit value to write
into memory for each palette index.
Until now, this code could only handle 8-bit visuals and didn't mask
overlapping values when ORing them.

With this patch, fbcon displays the correct colors when a qemu VM is
booted in 16-bit mode (in GRUB: "set gfxpayload=800x600x16").

Fixes: 7c83172b98e5 ("x86_64 EFI boot support: EFI frame buffer driver")  # v2.6.24+
Signed-off-by: Max Staudt <mstaudt@suse.de>
Acked-By: Peter Jones <pjones@redhat.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/video/efifb.c b/drivers/video/efifb.c
index 784139a..1bb5918 100644 (file)
--- a/drivers/video/efifb.c
+++ b/drivers/video/efifb.c
@@ -268,9 +268,9 @@ static int efifb_setcolreg(unsigned regno, unsigned red, unsigned green,
                return 1;
 
        if (regno < 16) {
-               red   >>= 8;
-               green >>= 8;
-               blue  >>= 8;
+               red   >>= 16 - info->var.red.length;
+               green >>= 16 - info->var.green.length;
+               blue  >>= 16 - info->var.blue.length;
                ((u32 *)(info->pseudo_palette))[regno] =
                        (red   << info->var.red.offset)   |
                        (green << info->var.green.offset) |