Phonet: zero-copy aligned GPRS RX

Newer Nokia cellular modems can use aligned payload for their GPRS pipe.
Signed-off-by: NRémi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/phonet/pep.h

@@ -77,6 +77,7 @@ static inline struct pnpipehdr *pnp_hdr(struct sk_buff *skb)
 
 enum {
 	PNS_PIPE_DATA = 0x20,
+	PNS_PIPE_ALIGNED_DATA,
 
 	PNS_PEP_CONNECT_REQ = 0x40,
 	PNS_PEP_CONNECT_RESP,

net/phonet/pep-gprs.c

@@ -96,11 +96,11 @@ static int gprs_recv(struct gprs_dev *gp, struct sk_buff *skb)
 		goto drop;
 	}
 
-	if (likely(skb_headroom(skb) & 3)) {
+	if (skb_headroom(skb) & 3) {
 		struct sk_buff *rskb, *fs;
 		int flen = 0;
 
-		/* Phonet Pipe data header is misaligned (3 bytes),
+		/* Phonet Pipe data header may be misaligned (3 bytes),
 		 * so wrap the IP packet as a single fragment of an head-less
 		 * socket buffer. The network stack will pull what it needs,
 		 * but at least, the whole IP payload is not memcpy'd. */

net/phonet/pep.c

@@ -354,6 +354,9 @@ static int pipe_do_rcv(struct sock *sk, struct sk_buff *skb)
 		queue = &pn->ctrlreq_queue;
 		goto queue;
 
+	case PNS_PIPE_ALIGNED_DATA:
+		__skb_pull(skb, 1);
+		/* fall through */
 	case PNS_PIPE_DATA:
 		__skb_pull(skb, 3); /* Pipe data header */
 		if (!pn_flow_safe(pn->rx_fc)) {