ieee802154: add ieee802154_skb_dst_pan helper

This patch adds ieee802154_skb_dst_pan function to get the pointer
address of the destination pan id at skb mac pointer.
Signed-off-by: Alexander Aring <aar@pengutronix.de>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

include/linux/ieee802154.h

@@ -31,6 +31,8 @@
 #define IEEE802154_MIN_PSDU_LEN		9
 #define IEEE802154_FCS_LEN		2
 #define IEEE802154_MAX_AUTH_TAG_LEN	16
+#define IEEE802154_FC_LEN		2
+#define IEEE802154_SEQ_LEN		1
 
 /*  General MAC frame format:
  *  2 bytes: Frame Control
@@ -221,9 +223,14 @@ enum {
 #define IEEE802154_FCTL_ACKREQ		0x0020
 #define IEEE802154_FCTL_SECEN		0x0004
 #define IEEE802154_FCTL_INTRA_PAN	0x0040
+#define IEEE802154_FCTL_DADDR		0x0c00
 
 #define IEEE802154_FTYPE_DATA		0x0001
 
+#define IEEE802154_FCTL_ADDR_NONE	0x0000
+#define IEEE802154_FCTL_DADDR_SHORT	0x0800
+#define IEEE802154_FCTL_DADDR_EXTENDED	0x0c00
+
 /*
  * ieee802154_is_data - check if type is IEEE802154_FTYPE_DATA
  * @fc: frame control bytes in little-endian byteorder
@@ -261,6 +268,15 @@ static inline bool ieee802154_is_intra_pan(__le16 fc)
 	return fc & cpu_to_le16(IEEE802154_FCTL_INTRA_PAN);
 }
 
+/*
+ * ieee802154_daddr_mode - get daddr mode from fc
+ * @fc: frame control bytes in little-endian byteorder
+ */
+static inline __le16 ieee802154_daddr_mode(__le16 fc)
+{
+	return fc & cpu_to_le16(IEEE802154_FCTL_DADDR);
+}
+
 /**
  * ieee802154_is_valid_psdu_len - check if psdu len is valid
  * available lengths:

include/net/mac802154.h

@@ -257,6 +257,35 @@ static inline __le16 ieee802154_get_fc_from_skb(const struct sk_buff *skb)
 	return get_unaligned_le16(skb_mac_header(skb));
 }
 
+/**
+ * ieee802154_skb_dst_pan - get the pointer to destination pan field
+ * @fc: mac header frame control field
+ * @skb: skb where the destination pan pointer will be get from
+ */
+static inline unsigned char *ieee802154_skb_dst_pan(__le16 fc,
+						    const struct sk_buff *skb)
+{
+	unsigned char *dst_pan;
+
+	switch (ieee802154_daddr_mode(fc)) {
+	case cpu_to_le16(IEEE802154_FCTL_ADDR_NONE):
+		dst_pan = NULL;
+		break;
+	case cpu_to_le16(IEEE802154_FCTL_DADDR_SHORT):
+	case cpu_to_le16(IEEE802154_FCTL_DADDR_EXTENDED):
+		dst_pan = skb_mac_header(skb) +
+			  IEEE802154_FC_LEN +
+			  IEEE802154_SEQ_LEN;
+		break;
+	default:
+		WARN_ONCE(1, "invalid addr mode detected");
+		dst_pan = NULL;
+		break;
+	}
+
+	return dst_pan;
+}
+
 /**
  * ieee802154_be64_to_le64 - copies and convert be64 to le64
  * @le64_dst: le64 destination pointer