linux-kernel - [PATCH] fbdev: Fix logic error in "offb" name match

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Message-ID: <f91c6079ef9764c7e23abd80ceab39a35f39417f.1759964186.git.fthain@linux-m68k.org>
Date: Thu, 09 Oct 2025 09:56:25 +1100
From: Finn Thain <fthain@...ux-m68k.org>
To: Simona Vetter <simona@...ll.ch>,
    Helge Deller <deller@....de>,
    Thomas Zimmermann <tzimmermann@...e.de>,
    Javier Martinez Canillas <javierm@...hat.com>
Cc: stable@...r.kernel.org,
    linux-fbdev@...r.kernel.org,
    dri-devel@...ts.freedesktop.org,
    linux-kernel@...r.kernel.org
Subject: [PATCH] fbdev: Fix logic error in "offb" name match

A regression was reported to me recently whereby /dev/fb0 had disappeared
from a PowerBook G3 Series "Wallstreet". The problem shows up when the
"video=ofonly" parameter is passed to the kernel, which is what the
bootloader does when "no video driver" is selected. The cause of the
problem is the "offb" string comparison, which got mangled when it got
refactored. Fix it.

Cc: stable@...r.kernel.org
Fixes: 93604a5ade3a ("fbdev: Handle video= parameter in video/cmdline.c")
Reported-and-tested-by: Stan Johnson <userm57@...oo.com>
Signed-off-by: Finn Thain <fthain@...ux-m68k.org>
---
 drivers/video/fbdev/core/fb_cmdline.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/core/fb_cmdline.c b/drivers/video/fbdev/core/fb_cmdline.c
index 4d1634c492ec..594b60424d1c 100644
--- a/drivers/video/fbdev/core/fb_cmdline.c
+++ b/drivers/video/fbdev/core/fb_cmdline.c
@@ -40,7 +40,7 @@ int fb_get_options(const char *name, char **option)
 	bool enabled;
 
 	if (name)
-		is_of = strncmp(name, "offb", 4);
+		is_of = !strncmp(name, "offb", 4);
 
 	enabled = __video_get_options(name, &options, is_of);
 
-- 
2.49.1