linux-kernel - Re: [PATCH pci-next v2 1/1] PCI/sysfs: Expose PCIe device serial number

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Message-ID: <20250716071618-b6d697c0-76e0-42f9-9937-7ba89e1792cc@linutronix.de>
Date: Wed, 16 Jul 2025 07:22:00 +0200
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Matthew Wood <thepacketgeek@...il.com>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH pci-next v2 1/1] PCI/sysfs: Expose PCIe device serial
 number

On Tue, Jul 15, 2025 at 09:53:22PM -0700, Matthew Wood 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 device_serial_number sysfs attribute will not be visible.
> 
> Signed-off-by: Matthew Wood <thepacketgeek@...il.com>
> ---
>  drivers/pci/pci-sysfs.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 268c69daa4d5..d59756bc91c9 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 device_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 -EINVAL;

-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);
> +}
> +static DEVICE_ATTR_RO(device_serial_number);
> +
>  static ssize_t secondary_bus_number_show(struct device *dev,
>  					 struct device_attribute *attr,
>  					 char *buf)
> @@ -660,6 +676,7 @@ 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_device_serial_number.attr,
>  	NULL,
>  };
>  
> @@ -1749,8 +1766,12 @@ 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))
> +	if (pci_is_pcie(pdev)) {
> +		if (strncmp(a->name, "device_serial_number", 20) == 0 &&

Compare to the real 'struct attribute *' instead of the name.
You could restructure this a bit to be easier to read.

if (!pci_is_pcie(pdev))
	return 0;

if (a == &dev_addr_device_serial_number.attr && !pci_get_dns(pdev))
	return 0;

return a->mode;

> +			!pci_get_dsn(pdev))
> +			return 0;
>  		return a->mode;
> +	}

Also should have some docs in Documentation/ABI/testing/sysfs-bus-pci.

>  
>  	return 0;
>  }
> -- 
> 2.50.0
>