On 10/28/25 11:50 AM, Thomas Zimmermann wrote:
Hi
Am 28.10.25 um 14:15 schrieb Mario Limonciello:
On 10/28/25 5:16 AM, Aaron Erhardt wrote:
On Mon, Aug 11, 2025 at 11:26:05AM -0500, Mario Limonciello (AMD) wrote:
On systems with non VGA GPUs fbcon can't find the primary GPU because
video_is_primary_device() only checks the VGA arbiter.
Add a screen info check to video_is_primary_device() so that callers
can get accurate data on such systems.
I have a question regarding this change. To me, the function name
video_is_primary_device() implies that there is only one primary GPU.
I would also expect that the 'boot_display' attribute added later in
the patch series based on this function is only set for one GPU, but
that is not necessarily the case. Since I'm working on a user-space
program that reads the 'boot_display' attribute, I need to know what
behavior is intended in order to do a correct implementation.
Reviewed-by: Thomas Zimmermann <[email protected]>
Suggested-by: Thomas Zimmermann <[email protected]>
Suggested-by: Bjorn Helgaas <[email protected]>
Signed-off-by: Mario Limonciello (AMD) <[email protected]>
---
v10:
* Rebase on 6.17-rc1
* Squash 'fbcon: Stop using screen_info_pci_dev()'
---
arch/x86/video/video-common.c | 25 ++++++++++++++++++++++++-
1 file changed, 24 insertions(+), 1 deletion(-)
diff --git a/arch/x86/video/video-common.c b/arch/x86/video/video-
common.c
index 81fc97a2a837a..e0aeee99bc99e 100644
--- a/arch/x86/video/video-common.c
+++ b/arch/x86/video/video-common.c
@@ -9,6 +9,7 @@
#include <linux/module.h>
#include <linux/pci.h>
+#include <linux/screen_info.h>
#include <linux/vgaarb.h>
#include <asm/video.h>
@@ -27,6 +28,11 @@ EXPORT_SYMBOL(pgprot_framebuffer);
bool video_is_primary_device(struct device *dev)
{
+#ifdef CONFIG_SCREEN_INFO
+ struct screen_info *si = &screen_info;
+ struct resource res[SCREEN_INFO_MAX_RESOURCES];
+ ssize_t i, numres;
+#endif
struct pci_dev *pdev;
if (!dev_is_pci(dev))
@@ -34,7 +40,24 @@ bool video_is_primary_device(struct device *dev)
pdev = to_pci_dev(dev);
- return (pdev == vga_default_device());
+ if (!pci_is_display(pdev))
+ return false;
+
+ if (pdev == vga_default_device())
+ return true;
This can mark a VGA device as primary GPU.
Is the value returned from vga_default_device() eq to NULL?
+
+#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 (pci_find_resource(pdev, &res[i]))
+ return true;
+ }
+#endif
And then the new code can also choose a primary GPU.
Maybe we should drop this block or move it to [1]? At [1] it would only
run if the more sophisticated vgaarb has been disabled.
The vgaarb now selects CONFIG_SCREEN_INFO and already tests for
overlapping resources. There's nothing here that vgaarb shouldn't
already do. Yet, I don't understand how only one of the can be true at a
time.
[1] https://elixir.bootlin.com/linux/v6.18-rc3/source/include/linux/
vgaarb.h#L55
There is a hunk at the end of vga_is_boot_device() which I think is
causing this issue. We have one VGA device which is NOT the boot
display but the code figures if it found nothing this must be right.
/*
* Vgadev has neither IO nor MEM enabled. If we haven't found any
* other VGA devices, it is the best candidate so far.
*/
if (!boot_vga)
return true;
I feel the right solution is to drop this now.
+
+ return false;
}
EXPORT_SYMBOL(video_is_primary_device);
In particular, I have hardware that has this exact configuration where
two GPUs are marked as primary and have a 'boot_display' attribute: the
first one through vga_default_device(), the second one through the new
detection method.
Is this intended?
Kind regards
Aaron
I wouldn't have expected a case like this and I think it means there
is a logic error.
Can you please file a kernel bugzilla with details about your system
and CC me?
dmesg and lspci -vvnn please
Also; please clarify which GPU shows something when booting up.
Agreed.
Best regards
Thomas
