PCI: Introduce pci_get_dsn

Several device drivers read their Device Serial Number from the PCIe
extended config space.

Introduce a new helper function, pci_get_dsn(). This function reads the
eight bytes of the DSN and returns them as a u64. If the capability does not
exist for the device, the function returns 0.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Cc: Michael Chan <michael.chan@broadcom.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 34 insertions, 0 deletions

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index c16b0ba2a895..86821313c007 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -580,6 +580,40 @@ int pci_find_ext_capability(struct pci_dev *dev, int cap)
 }
 EXPORT_SYMBOL_GPL(pci_find_ext_capability);
 
+/**
+ * pci_get_dsn - Read and return the 8-byte Device Serial Number
+ * @dev: PCI device to query
+ *
+ * Looks up the PCI_EXT_CAP_ID_DSN and reads the 8 bytes of the Device Serial
+ * Number.
+ *
+ * Returns the DSN, or zero if the capability does not exist.
+ */
+u64 pci_get_dsn(struct pci_dev *dev)
+{
+	u32 dword;
+	u64 dsn;
+	int pos;
+
+	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DSN);
+	if (!pos)
+		return 0;
+
+	/*
+	 * The Device Serial Number is two dwords offset 4 bytes from the
+	 * capability position. The specification says that the first dword is
+	 * the lower half, and the second dword is the upper half.
+	 */
+	pos += 4;
+	pci_read_config_dword(dev, pos, &dword);
+	dsn = (u64)dword;
+	pci_read_config_dword(dev, pos + 4, &dword);
+	dsn |= ((u64)dword) << 32;
+
+	return dsn;
+}
+EXPORT_SYMBOL_GPL(pci_get_dsn);
+
 static int __pci_find_next_ht_cap(struct pci_dev *dev, int pos, int ht_cap)
 {
 	int rc, ttl = PCI_FIND_CAP_TTL;