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([2001:df0:0:200c:e5ea:1a30:7c29:cd76]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-338778fb926sm4986048eec.31.2026.09.07.13.18.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Sep 2026 13:18:32 -0700 (PDT) Message-ID: <93ffe3ec-bb45-4c10-8d78-0cd23c9bb61e@gmail.com> Date: Tue, 8 Sep 2026 08:18:25 +1200 Precedence: bulk X-Mailing-List: linux-m68k@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] fbdev: atafb: Restrict SuperBlitter to supported formats To: Geert Uytterhoeven Cc: Linmao Li , deller@gmx.de, linux-fbdev@vger.kernel.org, miro.kropacek@gmail.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-m68k References: <20260827093948.2825531-1-lilinmao@kylinos.cn> Content-Language: en-US From: Michael Schmitz In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Hi Geert, On 7/09/26 20:38, Geert Uytterhoeven wrote: > Hi Michael, > > CC linux-m68k > > On Sun, 6 Sept 2026 at 03:49, Michael Schmitz wrote: >> 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); > This uses unaligned writes for the largest part. > You can avoid that by doing the memset32() first. True enough (iff line happens to be aligned, which is only true if rect->dx is even). But as Miro pointed out, 24 bpp can't actually be used (and without TOS setting such a mode before Linux boot, it can't ever happen). Cheers,     Michael > >> + 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 >>> --- >>> 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?? > I am no Atari expert, but IIRC all external framebuffers rely on > being fully set-up before Linux boots? > > Gr{oetje,eeting}s, > > Geert >