[PATCH v6 9/9] PCI: Add a new 'boot_display' attribute

[Thomas Zimmermann]

Hi

Am 27.06.25 um 06:31 schrieb Mario Limonciello:
> From: Mario Limonciello <mario.limonciello at amd.com>
>
> 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 at amd.com>
> ---
> 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 at vger.kernel.org>
> +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)