From 728b54528d37ffa27b07c9b181c5ed8d2d359379 Mon Sep 17 00:00:00 2001
From: Tj <tj.iam.tj@proton.me>
Date: Fri, 19 Jul 2024 19:50:56 +0200
Subject: [PATCH] xfree86: fbdevhw: fix pci detection on recent Linux

Linux kernel v6.9 has changed the symlink to point to the parent device. This
breaks fbdev_open() detection logic. Change it to use the subsystem symlink
instead which will remain stable.

Kernel v6.8:

[    14.067] (II) fbdev_open() sysfs_path=/sys/class/graphics/fb0
[    14.067] (II) fbdev_open() buf=../../devices/platform/vesa-framebuffer.0/graphics/fb0

Kernel v6.9:

[    15.609] (II) fbdev_open() sysfs_path=/sys/class/graphics/fb0
[    15.609] (II) fbdev_open() buf=../../devices/pci0000:00/0000:00:01.0/vesa-framebuffer.0/graphics/fb0

Originally found in automated Debian ISO QA testing [0] and confirmed in Linux [1].

Tested on kernels v6.9.7 and v6.8.12

[0] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1075713
[1] https://lore.kernel.org/lkml/lLyvPFC_APGHNfyGNHRpQy5izBikkaTPOpHooZIT3fFAoJPquSI31ZMueA99XTdr8ysir3X7O7IMdc6za-0m79vr_claeparHhoRouVgHOI=@proton.me/

Fixes: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1714
Signed-off-by: Tj <tj.iam.tj@proton.me>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1612>
---
 hw/xfree86/fbdevhw/fbdevhw.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/hw/xfree86/fbdevhw/fbdevhw.c b/hw/xfree86/fbdevhw/fbdevhw.c
index 1e39c81469..92cac3f4af 100644
--- a/hw/xfree86/fbdevhw/fbdevhw.c
+++ b/hw/xfree86/fbdevhw/fbdevhw.c
@@ -378,9 +378,9 @@ fbdev_open(int scrnIndex, const char *dev, char **namep)
         char *sysfs_path = NULL;
         char *node = strrchr(dev, '/') + 1;
 
-        if (asprintf(&sysfs_path, "/sys/class/graphics/%s", node) < 0 ||
+        if (asprintf(&sysfs_path, "/sys/class/graphics/%s/device/subsystem", node) < 0 ||
             readlink(sysfs_path, buf, sizeof(buf)) < 0 ||
-            strstr(buf, "devices/pci")) {
+            strstr(buf, "bus/pci")) {
             free(sysfs_path);
             close(fd);
             return -1;
-- 
GitLab

