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

[Michael Schmitz]

Hi Linmao,

thanks for your patch!

Am 27.08.2026 um 21:39 schrieb Linmao Li:
> 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.

> 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 <lilinmao@xxxxxxxxxx>
> ---
>  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;

Otherwise, LGTM.

@Geert: can you remember if pixel format or bit depth of an external 
framebuffer can be changed at runtime using fbset??

Reviewed-by: Michael Schmitz <schmitzmic@xxxxxxxxx>