Hi
Am 27.06.25 um 06:31 schrieb Mario Limonciello:
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>
---
v6:
* Only show for the device that is boot display
* Only create after PCI device sysfs files are initialized to ensure
that resources are ready.
v4:
* new patch
---
Documentation/ABI/testing/sysfs-bus-pci | 8 +++++
drivers/pci/pci-sysfs.c | 46 +++++++++++++++++++++++++
The code looks good. Just one more question: could this be added
independently from the PCI bus (at a reasonable cost)? There are other
busses that can host the boot display. Alternatively, we'd add this
attribute per bus as needed.
Best regards
Thomas
2 files changed, 54 insertions(+)
diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index 69f952fffec72..8b455b1a58852 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/Documentation/ABI/testing/sysfs-bus-pci
@@ -612,3 +612,11 @@ 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 the device was used as a boot
+ display. If the device was used as the boot display, the file
+ will be present and contain "1".
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 268c69daa4d57..cc766461de1da 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, "1\n");
+}
+static DEVICE_ATTR_RO(boot_display);
+
static ssize_t boot_vga_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
@@ -1246,6 +1254,37 @@ static int pci_create_attr(struct pci_dev *pdev, int num, int write_combine)
return 0;
}
+/**
+ * pci_create_boot_display_file - create a file in sysfs for @dev
+ * @pdev: dev in question
+ *
+ * Creates a file `boot_display` in sysfs for the PCI device @pdev
+ * if it is the boot display device.
+ */
+static int pci_create_boot_display_file(struct pci_dev *pdev)
+{
+#ifdef CONFIG_VIDEO
+ if (video_is_primary_device(&pdev->dev))
+ return sysfs_create_file(&pdev->dev.kobj, &dev_attr_boot_display.attr);
+#endif
+ return 0;
+}
+
+/**
+ * pci_remove_boot_display_file - remove the boot display file for @dev
+ * @pdev: dev in question
+ *
+ * Removes the file `boot_display` in sysfs for the PCI device @pdev
+ * if it is the boot display device.
+ */
+static void pci_remove_boot_display_file(struct pci_dev *pdev)
+{
+#ifdef CONFIG_VIDEO
+ if (video_is_primary_device(&pdev->dev))
+ sysfs_remove_file(&pdev->dev.kobj, &dev_attr_boot_display.attr);
+#endif
+}
+
/**
* pci_create_resource_files - create resource files in sysfs for @dev
* @pdev: dev in question
@@ -1654,9 +1693,15 @@ static const struct attribute_group pci_dev_resource_resize_group = {
int __must_check pci_create_sysfs_dev_files(struct pci_dev *pdev)
{
+ int retval;
+
if (!sysfs_initialized)
return -EACCES;
+ retval = pci_create_boot_display_file(pdev);
+ if (retval)
+ return retval;
+
return pci_create_resource_files(pdev);
}
@@ -1671,6 +1716,7 @@ void pci_remove_sysfs_dev_files(struct pci_dev *pdev)
if (!sysfs_initialized)
return;
+ pci_remove_boot_display_file(pdev);
pci_remove_resource_files(pdev);
}
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)
