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

[Matthew Wood <thepacketgeek@xxxxxxxxx>]

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>
Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
Reviewed-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
---
 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@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 = {
-- 
2.50.1