Re: [PATCH v8 1/1] PCI/sysfs: Expose PCI device serial number

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Sep 17, 2025 at 05:58:14AM -0700, Matthew Wood wrote:
> Add a single sysfs read-only interface for reading PCI device serial
> numbers from userspace in a programmatic way. This device attribute
> uses the same hexadecimal 1-byte dashed formatting as lspci serial number
> capability output. If a device doesn't support the serial number
> capability, the serial_number sysfs attribute will not be visible.
> 
> Signed-off-by: Matthew Wood <thepacketgeek@gmail.com>
> Reviewed-by: Mario Limonciello <superm1@kernel.org>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> Reviewed-by: Keith Busch <kbusch@kernel.org>
> Reviewed-by: Krzysztof Wilczyński <kwilczynski@kernel.org>

Applied to pci/misc for v6.18, thanks, and sorry for the inexcusable
delay.

> ---
>  Documentation/ABI/testing/sysfs-bus-pci |  9 +++++++++
>  drivers/pci/pci-sysfs.c                 | 21 +++++++++++++++++++++
>  2 files changed, 30 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
> index 69f952fffec7..92debe879ffb 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/.../serial_number
> +Date:		December 2025
> +Contact:	Matthew Wood <thepacketgeek@gmail.com>
> +Description:
> +		This is visible only for PCI devices that support the serial
> +		number extended capability. The file is read only and due to
> +		the possible sensitivity of accessible serial numbers, admin
> +		only.
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 268c69daa4d5..b7b7412c9f00 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 <linux/unaligned.h>
>  #include "pci.h"
>  
>  #ifndef ARCH_PCI_DEV_GROUPS
> @@ -694,6 +695,22 @@ static ssize_t boot_vga_show(struct device *dev, struct device_attribute *attr,
>  }
>  static DEVICE_ATTR_RO(boot_vga);
>  
> +static ssize_t serial_number_show(struct device *dev,
> +				  struct device_attribute *attr, char *buf)
> +{
> +	struct pci_dev *pci_dev = to_pci_dev(dev);
> +	u64 dsn;
> +	u8 bytes[8];
> +
> +	dsn = pci_get_dsn(pci_dev);
> +	if (!dsn)
> +		return -EIO;
> +	put_unaligned_be64(dsn, bytes);
> +
> +	return sysfs_emit(buf, "%8phD\n", bytes);
> +}
> +static DEVICE_ATTR_ADMIN_RO(serial_number);
> +
>  static ssize_t pci_read_config(struct file *filp, struct kobject *kobj,
>  			       const struct bin_attribute *bin_attr, char *buf,
>  			       loff_t off, size_t count)
> @@ -1698,6 +1715,7 @@ late_initcall(pci_sysfs_init);
>  
>  static struct attribute *pci_dev_dev_attrs[] = {
>  	&dev_attr_boot_vga.attr,
> +	&dev_attr_serial_number.attr,
>  	NULL,
>  };
>  
> @@ -1710,6 +1728,9 @@ 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;
>  
> +	if (a == &dev_attr_serial_number.attr && pci_get_dsn(pdev))
> +		return a->mode;
> +
>  	return 0;
>  }
>  
> -- 
> 2.50.1
>