Re: [PATCH] fbdev: atafb: Restrict SuperBlitter to supported formats
From: Michael Schmitz <schmitzmic@gmail.com>
Date: 2026-09-06 01:49:25
Also in:
dri-devel, lkml
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.
quoted hunk ↗ jump to hunk
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;
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@gmail.com>