On 6/26/2025 3:45 PM, Bjorn Helgaas wrote:
On Tue, Jun 24, 2025 at 03:30:42PM -0500, Mario Limonciello wrote:
From: Mario Limonciello <mario.limonciello@xxxxxxx>
On systems with multiple GPUs there can be uncertainty which GPU is the
primary one used to drive the display at bootup. In order to disambiguate
this add a new sysfs attribute 'boot_display' that uses the output of
video_is_primary_device() to populate whether a PCI device was used for
driving the display.
Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Question below.
---
v4:
* new patch
---
Documentation/ABI/testing/sysfs-bus-pci | 9 +++++++++
drivers/pci/pci-sysfs.c | 14 ++++++++++++++
2 files changed, 23 insertions(+)
diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index 69f952fffec72..897cfc1b0de0f 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/Documentation/ABI/testing/sysfs-bus-pci
@@ -612,3 +612,12 @@ Description:
# ls doe_features
0001:01 0001:02 doe_discovery
+
+What: /sys/bus/pci/devices/.../boot_display
+Date: October 2025
+Contact: Linux PCI developers <linux-pci@xxxxxxxxxxxxxxx>
+Description:
+ This file indicates whether the device was used as a boot
+ display. If the device was used as the boot display, the file
+ will contain "1". If the device is a display device but wasn't
+ used as a boot display, the file will contain "0".
Is there a reason to expose this file if it wasn't a boot display
device? Maybe it doesn't need to exist at all unless it contains "1"?
I was mostly thinking that it's a handy way for userspace to know
whether the kernel even supports this feature. If userspace sees that
file on any GPU as it walks a list then it knows it can use that for a hint.
But if you would rather it only shows up for the boot display yes it's
possible to do I think. It's just more complexity to the visibility
lookup to also call video_is_primary_device().
LMK which way you want to go and I'll respin the series with your tags
and the robot fix.
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 268c69daa4d57..5bbf79b1b953d 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -30,6 +30,7 @@
#include <linux/msi.h>
#include <linux/of.h>
#include <linux/aperture.h>
+#include <asm/video.h>
#include "pci.h"
#ifndef ARCH_PCI_DEV_GROUPS
@@ -679,6 +680,13 @@ const struct attribute_group *pcibus_groups[] = {
NULL,
};
+static ssize_t boot_display_show(struct device *dev, struct device_attribute *attr,
+ char *buf)
+{
+ return sysfs_emit(buf, "%u\n", video_is_primary_device(dev));
+}
+static DEVICE_ATTR_RO(boot_display);
+
static ssize_t boot_vga_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
@@ -1698,6 +1706,7 @@ late_initcall(pci_sysfs_init);
static struct attribute *pci_dev_dev_attrs[] = {
&dev_attr_boot_vga.attr,
+ &dev_attr_boot_display.attr,
NULL,
};
@@ -1710,6 +1719,11 @@ static umode_t pci_dev_attrs_are_visible(struct kobject *kobj,
if (a == &dev_attr_boot_vga.attr && pci_is_vga(pdev))
return a->mode;
+#ifdef CONFIG_VIDEO
+ if (a == &dev_attr_boot_display.attr && pci_is_display(pdev))
+ return a->mode;
+#endif
+
return 0;
}
--
2.43.0
