pci: Add helper to find a VPD resource data type

This patch adds the pci_vpd_find_tag() helper function to find VPD
resource data types in a buffer.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/pci/vpd.c

@@ -0,0 +1,43 @@
+/*
+ * File:	vpd.c
+ * Purpose:	Provide PCI VPD support
+ *
+ * Copyright (C) 2010 Broadcom Corporation.
+ */
+
+#include <linux/pci.h>
+
+int pci_vpd_find_tag(const u8 *buf, unsigned int off, unsigned int len, u8 rdt)
+{
+	int i;
+
+	for (i = off; i < len; ) {
+		u8 val = buf[i];
+
+		if (val & PCI_VPD_LRDT) {
+			/* Don't return success of the tag isn't complete */
+			if (i + PCI_VPD_LRDT_TAG_SIZE > len)
+				break;
+
+			if (val == rdt)
+				return i;
+
+			i += PCI_VPD_LRDT_TAG_SIZE +
+			     pci_vpd_lrdt_size(&buf[i]);
+		} else {
+			u8 tag = val & ~PCI_VPD_SRDT_LEN_MASK;
+
+			if (tag == rdt)
+				return i;
+
+			if (tag == PCI_VPD_SRDT_END)
+				break;
+
+			i += PCI_VPD_SRDT_TAG_SIZE +
+			     pci_vpd_srdt_size(&buf[i]);
+		}
+	}
+
+	return -ENOENT;
+}
+EXPORT_SYMBOL_GPL(pci_vpd_find_tag);