[U-Boot] [PATCH V3] cfb_console: align fields in gzipped .bmp files

[Eric Nelson <eric.nelson@boundarydevices.com>]

.bmp files contain 32-bit integers aligned at offsets of +2, +6,
et cetera within the bmp_header structure (see include/bmp_layout.h).

Support for gzip-compressed .bmp files is present in the cfb_console
display subsystem by uncompressing them prior to use.

This patch forces the in-memory header to be aligned properly
for these compressed images by extracting them to a 2-byte
offset in the memory returned by malloc. Since malloc will always
return a 4-byte aligned value, this forces the .bmp header
fields to be naturally aligned on 4-byte addresses.

Refer to these files for more details:
	doc/README.displaying-bmps
	doc/README.arm-unaligned-accesses

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
---
Changes in V2:
    - re-worded the subject line
    - expanded and re-worded the commit message
Changes in V3:
    - shortened the subject line
    - fixed multiline comment style
    - added patch history
    - sent with "In-Reply-To" header referring to V1
      See also:
        V1: http://patchwork.ozlabs.org/patch/323243/
        V2: http://patchwork.ozlabs.org/patch/325348/

 drivers/video/cfb_console.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/video/cfb_console.c b/drivers/video/cfb_console.c
index 6db4073..b52e9ed 100644
--- a/drivers/video/cfb_console.c
+++ b/drivers/video/cfb_console.c
@@ -1473,7 +1473,11 @@ int video_display_bitmap(ulong bmp_image, int x, int y)
 			printf("Error: malloc in gunzip failed!\n");
 			return 1;
 		}
-		if (gunzip(dst, CONFIG_SYS_VIDEO_LOGO_MAX_SIZE,
+		/*
+		 * NB: we need to force offset of +2
+		 * See doc/README.displaying-bmps
+		 */
+		if (gunzip(dst+2, CONFIG_SYS_VIDEO_LOGO_MAX_SIZE-2,
 			   (uchar *) bmp_image,
 			   &len) != 0) {
 			printf("Error: no valid bmp or bmp.gz image at %lx\n",
@@ -1489,7 +1493,7 @@ int video_display_bitmap(ulong bmp_image, int x, int y)
 		/*
 		 * Set addr to decompressed image
 		 */
-		bmp = (bmp_image_t *) dst;
+		bmp = (bmp_image_t *)(dst+2);
 
 		if (!((bmp->header.signature[0] == 'B') &&
 		      (bmp->header.signature[1] == 'M'))) {
-- 
1.8.3.2