[PATCH] fbdev: atafb: Restrict SuperBlitter to supported formats

The SuperBlitter operations derive an integer byte count per pixel.  The
accelerated fill path handles only one-, two- and four-byte pixels.
However, the operations are currently installed for every external
framebuffer in SuperVidel RAM, including planar 1/2/4/8-bpp and 24-bpp
truecolor modes accepted by the external video parser.

For 1/2/4-bpp modes, the byte count becomes zero, so accelerated copies do
nothing and fills fall through to 32-bit stores.  Planar 8-bpp uses an
incompatible memory layout.  For 24-bpp modes, fills also use 32-bit stores
despite advancing addresses by three bytes per pixel.  These cases can
corrupt the framebuffer beyond the requested rectangle.

Enable the SuperBlitter operations only for the layouts they implement:
8-bpp packed pixels and 16/32-bpp truecolor.  Keep the existing software
operations for all other external formats.

Fixes: d463633d63e6 ("fbdev: atafb: Add support for SuperVidel's SuperBlitter")
Signed-off-by: Linmao Li <redacted>
---
 drivers/video/fbdev/atafb.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/atafb.c b/drivers/video/fbdev/atafb.c
index 5bca34c45cef3..c3011b61a94b9 100644
--- a/drivers/video/fbdev/atafb.c
+++ b/drivers/video/fbdev/atafb.c

@@ -3360,7 +3360,11 @@ static int __init atafb_probe(struct platform_device *pdev)
 		memset (screen_base, 0, external_len);
 
 		/* framebuffer in SV RAM: enable the SuperBlitter */
-		if (external_addr >= 0xa0000000) {
+		if (external_addr >= 0xa0000000 &&
+		    ((external_pmode == FB_TYPE_PACKED_PIXELS &&
+		      external_depth == 8) ||
+		     (external_pmode == -1 &&
+		      (external_depth == 16 || external_depth == 32)))) {
 			svblit_regs = ioremap(SVBLIT_REGS_PHYS, 0x100);
 			if (svblit_regs) {
 				svblit_fw = svblit_rd(SVBLIT_VERSION) & 0x1ff;

-- 
2.25.1