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

Hi Linmao,

thanks for your patch!

Am 27.08.2026 um 21:39 schrieb Linmao Li:

quoted

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.

I believe 24 bpp mode can be rescued using something like this (entirely
untested):

--- a/drivers/video/fbdev/atafb.c
+++ b/drivers/video/fbdev/atafb.c

@@ -2463,6 +2463,11 @@ static void svblit_fillrect(struct fb_info *info,
         case 2:
                 memset16((u16 *)line, pix, rect->width);
                 break;
+       case 3:
+               memset(line, pix, ((rect->width * bytespp) % 4));
+               line += ((rect->width * bytespp) % 4);
+               memset32((u32 *)line, pix, (rect->width * bytespp) / 4);
+               break;
         default:
                 memset32((u32 *)line, pix, rect->width);
                 break;

Can't test this on hardware, and would need Miro to confirm it works as
intended.