Re: [RESEND PATCH v7 1/1] PCI/sysfs: Expose PCIe device serial number

[Hans Zhang <hans.zhang@cixtech.com>]

On 2025/8/22 07:22, Matthew Wood wrote:
> EXTERNAL EMAIL
> 
> 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@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>

Tested-by: Hans Zhang <hans.zhang@cixtech.com>

Best regards,
Hans

> ---
>   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..d5251f4f3659 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 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 = {
> --
> 2.50.1
> 
>