Re: [PATCH v5 1/1] PCI/sysfs: Expose PCIe device serial number

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Thu, 17 Jul 2025 09:50:54 -0700
Matthew Wood <thepacketgeek@gmail.com> 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@gmail.com>
> Reviewed-by: Mario Limonciello <superm1@kernel.org>
Hi Matthew,

A suggestion inline.  I'm also fine with the current version if that's
what people feel more comfortable with.

If we stick to what you have here
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>

Jonathan

> ---
>  Documentation/ABI/testing/sysfs-bus-pci |  9 +++++++++
>  drivers/pci/pci-sysfs.c                 | 26 ++++++++++++++++++++++---
>  2 files changed, 32 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@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..bc0e0add15d1 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -239,6 +239,22 @@ 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;
> +
> +	dsn = pci_get_dsn(pci_dev);
> +	if (!dsn)
> +		return -EIO;
> +
> +	return sysfs_emit(buf, "%02llx-%02llx-%02llx-%02llx-%02llx-%02llx-%02llx-%02llx\n",
> +		dsn >> 56, (dsn >> 48) & 0xff, (dsn >> 40) & 0xff, (dsn >> 32) & 0xff,
> +		(dsn >> 24) & 0xff, (dsn >> 16) & 0xff, (dsn >> 8) & 0xff, dsn & 0xff);

I wonder if doing the following i too esoteric. Eyeballing those shifts is painful.

	u8 bytewise[8]; /* naming hard... */

	put_unaligned_u64(dsn, bytewise);

	return sysfs_emit(buf, "%02x-%02x-%02x-%02x-%02x-%02x-%02x-%02x\n",
		bytewise[0], bytewise[1], bytewise[2], bytewise[3],
		bytewise[4], bytewise[5], bytewise[6], bytewise[7]);


> +}
> +static DEVICE_ATTR_ADMIN_RO(serial_number);