[SRU][R/S][PATCH 1/1] x86/video: Only fall back to vga_default_device() without screen info

[Aaron Ma]

From: Mario Limonciello <mario.limonciello at amd.com>

BugLink: https://bugs.launchpad.net/bugs/2161036

Some multi GPU systems may have a VGA compatible device, but that might not be
used for display.  If due to enumeration order this device is found before the
one actually used for display then multiple devices may show the boot_display
attribute, confusing userspace.

When screen info is valid, use it exclusively to find the primary device so
that only the device backing the framebuffer is reported.  Only when no
framebuffer has been set up does it make sense to fall back to the default VGA
device.  This ensures at most one primary graphics device, preferably the one
with the framebuffer.

Fixes: ad90860bd10ee ("fbcon: Use screen info to find primary device")
Closes: https://lore.kernel.org/linux-pci/20260618081803.2790848-1-aaron.ma@canonical.com/#t
Reported-by: Aaron Ma <aaron.ma at canonical.com>
Suggested-by: Thomas Zimmermann <tzimmermann at suse.de>
Signed-off-by: Mario Limonciello <mario.limonciello at amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp at alien8.de>
Reviewed-by: Thomas Zimmermann <tzimmermann at suse.de>
Tested-by: Aaron Ma <aaron.ma at canonical.com>
Cc: <stable at kernel.org>
Link: https://patch.msgid.link/20260623141505.1816786-1-mario.limonciello@amd.com
(cherry picked from commit 596b3678326d3d1aed7c19423b6746f1ce09688a)
Signed-off-by: Aaron Ma <aaron.ma at canonical.com>
---
 arch/x86/video/video-common.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/arch/x86/video/video-common.c b/arch/x86/video/video-common.c
index e0aeee99bc99e..e5fb3cf885fbd 100644
--- a/arch/x86/video/video-common.c
+++ b/arch/x86/video/video-common.c
@@ -43,21 +43,26 @@ bool video_is_primary_device(struct device *dev)
 	if (!pci_is_display(pdev))
 		return false;
 
-	if (pdev == vga_default_device())
-		return true;
-
 #ifdef CONFIG_SCREEN_INFO
 	numres = screen_info_resources(si, res, ARRAY_SIZE(res));
-	for (i = 0; i < numres; ++i) {
-		if (!(res[i].flags & IORESOURCE_MEM))
-			continue;
+	if (numres > 0) {
+		for (i = 0; i < numres; ++i) {
+			if (!(res[i].flags & IORESOURCE_MEM))
+				continue;
+
+			if (pci_find_resource(pdev, &res[i]))
+				return true;
+		}
 
-		if (pci_find_resource(pdev, &res[i]))
-			return true;
+		return false;
 	}
 #endif
 
-	return false;
+	/*
+	 * No framebuffer was set up by the firmware/bootloader, so fall back
+	 * to the default VGA device.
+	 */
+	return pdev == vga_default_device();
 }
 EXPORT_SYMBOL(video_is_primary_device);
 
-- 
2.43.0