On Fri, 18 Jul 2025 12:32:29 -0700
Matthew Wood <thepacketgeek@xxxxxxxxx> wrote:
> Add a single sysfs read-only interface for reading PCIe 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@xxxxxxxxx>
> Reviewed-by: Mario Limonciello <superm1@xxxxxxxxxx>
Nice. The %8phD that Thomas pointed out was new to me. Very useful!
Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
> ---
> Documentation/ABI/testing/sysfs-bus-pci | 9 +++++++++
> drivers/pci/pci-sysfs.c | 27 ++++++++++++++++++++++---
> 2 files changed, 33 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
> index 69f952fffec7..0a2580cdd58c 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: October 2025
> +Contact: Matthew Wood <thepacketgeek@xxxxxxxxx>
> +Description:
> + This is visible only for PCIe 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..1d26e4336f1b 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
> @@ -239,6 +240,22 @@ static ssize_t current_link_width_show(struct device *dev,
> }
> static DEVICE_ATTR_RO(current_link_width);
>
> +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 secondary_bus_number_show(struct device *dev,
> struct device_attribute *attr,
> char *buf)
> @@ -660,6 +677,7 @@ static struct attribute *pcie_dev_attrs[] = {
> &dev_attr_current_link_width.attr,
> &dev_attr_max_link_width.attr,
> &dev_attr_max_link_speed.attr,
> + &dev_attr_serial_number.attr,
> NULL,
> };
>
> @@ -1749,10 +1767,13 @@ static umode_t pcie_dev_attrs_are_visible(struct kobject *kobj,
> struct device *dev = kobj_to_dev(kobj);
> struct pci_dev *pdev = to_pci_dev(dev);
>
> - if (pci_is_pcie(pdev))
> - return a->mode;
> + if (!pci_is_pcie(pdev))
> + return 0;
>
> - return 0;
> + if (a == &dev_attr_serial_number.attr && !pci_get_dsn(pdev))
> + return 0;
> +
> + return a->mode;
> }
>
> static const struct attribute_group pci_dev_group = {
