NFC: Add an shdlc llc module to llc core

This is used by HCI drivers such as the one for the pn544 which require
communications between HCI and the chip to use shdlc.
Signed-off-by: NEric Lapuyade <eric.lapuyade@intel.com>
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>

include/net/nfc/llc.h

@@ -25,6 +25,7 @@
 #include <linux/skbuff.h>
 
 #define LLC_NOP_NAME "nop"
+#define LLC_SHDLC_NAME "shdlc"
 
 typedef void (*rcv_to_hci_t) (struct nfc_hci_dev *hdev, struct sk_buff *skb);
 typedef int (*xmit_to_drv_t) (struct nfc_hci_dev *hdev, struct sk_buff *skb);

net/nfc/hci/Makefile

@@ -5,4 +5,4 @@
 obj-$(CONFIG_NFC_HCI) += hci.o
 
 hci-y			:= core.o hcp.o command.o llc.o llc_nop.o
-hci-$(CONFIG_NFC_SHDLC)	+= shdlc.o
+hci-$(CONFIG_NFC_SHDLC) += shdlc.o llc_shdlc.o

net/nfc/hci/llc.c

@@ -26,9 +26,23 @@ static struct list_head llc_engines;
 
 int nfc_llc_init(void)
 {
+	int r;
+
 	INIT_LIST_HEAD(&llc_engines);
 
-	return nfc_llc_nop_register();
+	r = nfc_llc_nop_register();
+	if (r)
+		goto exit;
+
+	r = nfc_llc_shdlc_register();
+	if (r)
+		goto exit;
+
+	return 0;
+
+exit:
+	nfc_llc_exit();
+	return r;
 }
 EXPORT_SYMBOL(nfc_llc_init);
 

net/nfc/hci/llc.h

@@ -56,5 +56,6 @@ int nfc_llc_register(const char *name, struct nfc_llc_ops *ops);
 void nfc_llc_unregister(const char *name);
 
 int nfc_llc_nop_register(void);
+int nfc_llc_shdlc_register(void);
 
 #endif /* __LOCAL_LLC_H_ */

net/nfc/hci/llc_shdlc.c

+/*
+ * shdlc Link Layer Control
+ *
+ * Copyright (C) 2012  Intel Corporation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the
+ * Free Software Foundation, Inc.,
+ * 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ */
+
+#define pr_fmt(fmt) "shdlc: %s: " fmt, __func__
+
+#include <linux/types.h>
+#include <linux/sched.h>
+#include <linux/export.h>
+#include <linux/wait.h>
+#include <linux/slab.h>
+#include <linux/skbuff.h>
+
+#include "llc.h"
+
+enum shdlc_state {
+	SHDLC_DISCONNECTED = 0,
+	SHDLC_CONNECTING = 1,
+	SHDLC_NEGOCIATING = 2,
+	SHDLC_CONNECTED = 3
+};
+
+struct llc_shdlc {
+	struct nfc_hci_dev *hdev;
+	xmit_to_drv_t xmit_to_drv;
+	rcv_to_hci_t rcv_to_hci;
+
+	struct mutex state_mutex;
+	enum shdlc_state state;
+	int hard_fault;
+
+	wait_queue_head_t *connect_wq;
+	int connect_tries;
+	int connect_result;
+	struct timer_list connect_timer;/* aka T3 in spec 10.6.1 */
+
+	u8 w;				/* window size */
+	bool srej_support;
+
+	struct timer_list t1_timer;	/* send ack timeout */
+	bool t1_active;
+
+	struct timer_list t2_timer;	/* guard/retransmit timeout */
+	bool t2_active;
+
+	int ns;				/* next seq num for send */
+	int nr;				/* next expected seq num for receive */
+	int dnr;			/* oldest sent unacked seq num */
+
+	struct sk_buff_head rcv_q;
+
+	struct sk_buff_head send_q;
+	bool rnr;			/* other side is not ready to receive */
+
+	struct sk_buff_head ack_pending_q;
+
+	struct work_struct sm_work;
+
+	int tx_headroom;
+	int tx_tailroom;
+
+	llc_failure_t llc_failure;
+};
+
+#define SHDLC_LLC_HEAD_ROOM	2
+
+#define SHDLC_MAX_WINDOW	4
+#define SHDLC_SREJ_SUPPORT	false
+
+#define SHDLC_CONTROL_HEAD_MASK	0xe0
+#define SHDLC_CONTROL_HEAD_I	0x80
+#define SHDLC_CONTROL_HEAD_I2	0xa0
+#define SHDLC_CONTROL_HEAD_S	0xc0
+#define SHDLC_CONTROL_HEAD_U	0xe0
+
+#define SHDLC_CONTROL_NS_MASK	0x38
+#define SHDLC_CONTROL_NR_MASK	0x07
+#define SHDLC_CONTROL_TYPE_MASK	0x18
+
+#define SHDLC_CONTROL_M_MASK	0x1f
+
+enum sframe_type {
+	S_FRAME_RR = 0x00,
+	S_FRAME_REJ = 0x01,
+	S_FRAME_RNR = 0x02,
+	S_FRAME_SREJ = 0x03
+};
+
+enum uframe_modifier {
+	U_FRAME_UA = 0x06,
+	U_FRAME_RSET = 0x19
+};
+
+#define SHDLC_CONNECT_VALUE_MS	5
+#define SHDLC_T1_VALUE_MS(w)	((5 * w) / 4)
+#define SHDLC_T2_VALUE_MS	300
+
+#define SHDLC_DUMP_SKB(info, skb)				  \
+do {								  \
+	pr_debug("%s:\n", info);				  \
+	print_hex_dump(KERN_DEBUG, "shdlc: ", DUMP_PREFIX_OFFSET, \
+		       16, 1, skb->data, skb->len, 0);		  \
+} while (0)
+
+/* checks x < y <= z modulo 8 */
+static bool llc_shdlc_x_lt_y_lteq_z(int x, int y, int z)
+{
+	if (x < z)
+		return ((x < y) && (y <= z)) ? true : false;
+	else
+		return ((y > x) || (y <= z)) ? true : false;
+}
+
+/* checks x <= y < z modulo 8 */
+static bool llc_shdlc_x_lteq_y_lt_z(int x, int y, int z)
+{
+	if (x <= z)
+		return ((x <= y) && (y < z)) ? true : false;
+	else			/* x > z -> z+8 > x */
+		return ((y >= x) || (y < z)) ? true : false;
+}
+
+static struct sk_buff *llc_shdlc_alloc_skb(struct llc_shdlc *shdlc,
+					   int payload_len)
+{
+	struct sk_buff *skb;
+
+	skb = alloc_skb(shdlc->tx_headroom + SHDLC_LLC_HEAD_ROOM +
+			shdlc->tx_tailroom + payload_len, GFP_KERNEL);
+	if (skb)
+		skb_reserve(skb, shdlc->tx_headroom + SHDLC_LLC_HEAD_ROOM);
+
+	return skb;
+}
+
+/* immediately sends an S frame. */
+static int llc_shdlc_send_s_frame(struct llc_shdlc *shdlc,
+				  enum sframe_type sframe_type, int nr)
+{
+	int r;
+	struct sk_buff *skb;
+
+	pr_debug("sframe_type=%d nr=%d\n", sframe_type, nr);
+
+	skb = llc_shdlc_alloc_skb(shdlc, 0);
+	if (skb == NULL)
+		return -ENOMEM;
+
+	*skb_push(skb, 1) = SHDLC_CONTROL_HEAD_S | (sframe_type << 3) | nr;
+
+	r = shdlc->xmit_to_drv(shdlc->hdev, skb);
+
+	kfree_skb(skb);
+
+	return r;
+}
+
+/* immediately sends an U frame. skb may contain optional payload */
+static int llc_shdlc_send_u_frame(struct llc_shdlc *shdlc,
+				  struct sk_buff *skb,
+				  enum uframe_modifier uframe_modifier)
+{
+	int r;
+
+	pr_debug("uframe_modifier=%d\n", uframe_modifier);
+
+	*skb_push(skb, 1) = SHDLC_CONTROL_HEAD_U | uframe_modifier;
+
+	r = shdlc->xmit_to_drv(shdlc->hdev, skb);
+
+	kfree_skb(skb);
+
+	return r;
+}
+
+/*
+ * Free ack_pending frames until y_nr - 1, and reset t2 according to
+ * the remaining oldest ack_pending frame sent time
+ */
+static void llc_shdlc_reset_t2(struct llc_shdlc *shdlc, int y_nr)
+{
+	struct sk_buff *skb;
+	int dnr = shdlc->dnr;	/* MUST initially be < y_nr */
+
+	pr_debug("release ack pending up to frame %d excluded\n", y_nr);
+
+	while (dnr != y_nr) {
+		pr_debug("release ack pending frame %d\n", dnr);
+
+		skb = skb_dequeue(&shdlc->ack_pending_q);
+		kfree_skb(skb);
+
+		dnr = (dnr + 1) % 8;
+	}
+
+	if (skb_queue_empty(&shdlc->ack_pending_q)) {
+		if (shdlc->t2_active) {
+			del_timer_sync(&shdlc->t2_timer);
+			shdlc->t2_active = false;
+
+			pr_debug
+			    ("All sent frames acked. Stopped T2(retransmit)\n");
+		}
+	} else {
+		skb = skb_peek(&shdlc->ack_pending_q);
+
+		mod_timer(&shdlc->t2_timer, *(unsigned long *)skb->cb +
+			  msecs_to_jiffies(SHDLC_T2_VALUE_MS));
+		shdlc->t2_active = true;
+
+		pr_debug
+		    ("Start T2(retransmit) for remaining unacked sent frames\n");
+	}
+}
+
+/*
+ * Receive validated frames from lower layer. skb contains HCI payload only.
+ * Handle according to algorithm at spec:10.8.2
+ */
+static void llc_shdlc_rcv_i_frame(struct llc_shdlc *shdlc,
+				  struct sk_buff *skb, int ns, int nr)
+{
+	int x_ns = ns;
+	int y_nr = nr;
+
+	pr_debug("recvd I-frame %d, remote waiting frame %d\n", ns, nr);
+
+	if (shdlc->state != SHDLC_CONNECTED)
+		goto exit;
+
+	if (x_ns != shdlc->nr) {
+		llc_shdlc_send_s_frame(shdlc, S_FRAME_REJ, shdlc->nr);
+		goto exit;
+	}
+
+	if (shdlc->t1_active == false) {
+		shdlc->t1_active = true;
+		mod_timer(&shdlc->t1_timer, jiffies +
+			  msecs_to_jiffies(SHDLC_T1_VALUE_MS(shdlc->w)));
+		pr_debug("(re)Start T1(send ack)\n");
+	}
+
+	if (skb->len) {
+		shdlc->rcv_to_hci(shdlc->hdev, skb);
+		skb = NULL;
+	}
+
+	shdlc->nr = (shdlc->nr + 1) % 8;
+
+	if (llc_shdlc_x_lt_y_lteq_z(shdlc->dnr, y_nr, shdlc->ns)) {
+		llc_shdlc_reset_t2(shdlc, y_nr);
+
+		shdlc->dnr = y_nr;
+	}
+
+exit:
+	kfree_skb(skb);
+}
+
+static void llc_shdlc_rcv_ack(struct llc_shdlc *shdlc, int y_nr)
+{
+	pr_debug("remote acked up to frame %d excluded\n", y_nr);
+
+	if (llc_shdlc_x_lt_y_lteq_z(shdlc->dnr, y_nr, shdlc->ns)) {
+		llc_shdlc_reset_t2(shdlc, y_nr);
+		shdlc->dnr = y_nr;
+	}
+}
+
+static void llc_shdlc_requeue_ack_pending(struct llc_shdlc *shdlc)
+{
+	struct sk_buff *skb;
+
+	pr_debug("ns reset to %d\n", shdlc->dnr);
+
+	while ((skb = skb_dequeue_tail(&shdlc->ack_pending_q))) {
+		skb_pull(skb, 1);	/* remove control field */
+		skb_queue_head(&shdlc->send_q, skb);
+	}
+	shdlc->ns = shdlc->dnr;
+}
+
+static void llc_shdlc_rcv_rej(struct llc_shdlc *shdlc, int y_nr)
+{
+	struct sk_buff *skb;
+
+	pr_debug("remote asks retransmition from frame %d\n", y_nr);
+
+	if (llc_shdlc_x_lteq_y_lt_z(shdlc->dnr, y_nr, shdlc->ns)) {
+		if (shdlc->t2_active) {
+			del_timer_sync(&shdlc->t2_timer);
+			shdlc->t2_active = false;
+			pr_debug("Stopped T2(retransmit)\n");
+		}
+
+		if (shdlc->dnr != y_nr) {
+			while ((shdlc->dnr = ((shdlc->dnr + 1) % 8)) != y_nr) {
+				skb = skb_dequeue(&shdlc->ack_pending_q);
+				kfree_skb(skb);
+			}
+		}
+
+		llc_shdlc_requeue_ack_pending(shdlc);
+	}
+}
+
+/* See spec RR:10.8.3 REJ:10.8.4 */
+static void llc_shdlc_rcv_s_frame(struct llc_shdlc *shdlc,
+				  enum sframe_type s_frame_type, int nr)
+{
+	struct sk_buff *skb;
+
+	if (shdlc->state != SHDLC_CONNECTED)
+		return;
+
+	switch (s_frame_type) {
+	case S_FRAME_RR:
+		llc_shdlc_rcv_ack(shdlc, nr);
+		if (shdlc->rnr == true) {	/* see SHDLC 10.7.7 */
+			shdlc->rnr = false;
+			if (shdlc->send_q.qlen == 0) {
+				skb = llc_shdlc_alloc_skb(shdlc, 0);
+				if (skb)
+					skb_queue_tail(&shdlc->send_q, skb);
+			}
+		}
+		break;
+	case S_FRAME_REJ:
+		llc_shdlc_rcv_rej(shdlc, nr);
+		break;
+	case S_FRAME_RNR:
+		llc_shdlc_rcv_ack(shdlc, nr);
+		shdlc->rnr = true;
+		break;
+	default:
+		break;
+	}
+}
+
+static void llc_shdlc_connect_complete(struct llc_shdlc *shdlc, int r)
+{
+	pr_debug("result=%d\n", r);
+
+	del_timer_sync(&shdlc->connect_timer);
+
+	if (r == 0) {
+		shdlc->ns = 0;
+		shdlc->nr = 0;
+		shdlc->dnr = 0;
+
+		shdlc->state = SHDLC_CONNECTED;
+	} else {
+		shdlc->state = SHDLC_DISCONNECTED;
+	}
+
+	shdlc->connect_result = r;
+
+	wake_up(shdlc->connect_wq);
+}
+
+static int llc_shdlc_connect_initiate(struct llc_shdlc *shdlc)
+{
+	struct sk_buff *skb;
+
+	pr_debug("\n");
+
+	skb = llc_shdlc_alloc_skb(shdlc, 2);
+	if (skb == NULL)
+		return -ENOMEM;
+
+	*skb_put(skb, 1) = SHDLC_MAX_WINDOW;
+	*skb_put(skb, 1) = SHDLC_SREJ_SUPPORT ? 1 : 0;
+
+	return llc_shdlc_send_u_frame(shdlc, skb, U_FRAME_RSET);
+}
+
+static int llc_shdlc_connect_send_ua(struct llc_shdlc *shdlc)
+{
+	struct sk_buff *skb;
+
+	pr_debug("\n");
+
+	skb = llc_shdlc_alloc_skb(shdlc, 0);
+	if (skb == NULL)
+		return -ENOMEM;
+
+	return llc_shdlc_send_u_frame(shdlc, skb, U_FRAME_UA);
+}
+
+static void llc_shdlc_rcv_u_frame(struct llc_shdlc *shdlc,
+				  struct sk_buff *skb,
+				  enum uframe_modifier u_frame_modifier)
+{
+	u8 w = SHDLC_MAX_WINDOW;
+	bool srej_support = SHDLC_SREJ_SUPPORT;
+	int r;
+
+	pr_debug("u_frame_modifier=%d\n", u_frame_modifier);
+
+	switch (u_frame_modifier) {
+	case U_FRAME_RSET:
+		if (shdlc->state == SHDLC_NEGOCIATING) {
+			/* we sent RSET, but chip wants to negociate */
+			if (skb->len > 0)
+				w = skb->data[0];
+
+			if (skb->len > 1)
+				srej_support = skb->data[1] & 0x01 ? true :
+					       false;
+
+			if ((w <= SHDLC_MAX_WINDOW) &&
+			    (SHDLC_SREJ_SUPPORT || (srej_support == false))) {
+				shdlc->w = w;
+				shdlc->srej_support = srej_support;
+				r = llc_shdlc_connect_send_ua(shdlc);
+				llc_shdlc_connect_complete(shdlc, r);
+			}
+		} else if (shdlc->state == SHDLC_CONNECTED) {
+			/*
+			 * Chip wants to reset link. This is unexpected and
+			 * unsupported.
+			 */
+			shdlc->hard_fault = -ECONNRESET;
+		}
+		break;
+	case U_FRAME_UA:
+		if ((shdlc->state == SHDLC_CONNECTING &&
+		     shdlc->connect_tries > 0) ||
+		    (shdlc->state == SHDLC_NEGOCIATING))
+			llc_shdlc_connect_complete(shdlc, 0);
+		break;
+	default:
+		break;
+	}
+
+	kfree_skb(skb);
+}
+
+static void llc_shdlc_handle_rcv_queue(struct llc_shdlc *shdlc)
+{
+	struct sk_buff *skb;
+	u8 control;
+	int nr;
+	int ns;
+	enum sframe_type s_frame_type;
+	enum uframe_modifier u_frame_modifier;
+
+	if (shdlc->rcv_q.qlen)
+		pr_debug("rcvQlen=%d\n", shdlc->rcv_q.qlen);
+
+	while ((skb = skb_dequeue(&shdlc->rcv_q)) != NULL) {
+		control = skb->data[0];
+		skb_pull(skb, 1);
+		switch (control & SHDLC_CONTROL_HEAD_MASK) {
+		case SHDLC_CONTROL_HEAD_I:
+		case SHDLC_CONTROL_HEAD_I2:
+			ns = (control & SHDLC_CONTROL_NS_MASK) >> 3;
+			nr = control & SHDLC_CONTROL_NR_MASK;
+			llc_shdlc_rcv_i_frame(shdlc, skb, ns, nr);
+			break;
+		case SHDLC_CONTROL_HEAD_S:
+			s_frame_type = (control & SHDLC_CONTROL_TYPE_MASK) >> 3;
+			nr = control & SHDLC_CONTROL_NR_MASK;
+			llc_shdlc_rcv_s_frame(shdlc, s_frame_type, nr);
+			kfree_skb(skb);
+			break;
+		case SHDLC_CONTROL_HEAD_U:
+			u_frame_modifier = control & SHDLC_CONTROL_M_MASK;
+			llc_shdlc_rcv_u_frame(shdlc, skb, u_frame_modifier);
+			break;
+		default:
+			pr_err("UNKNOWN Control=%d\n", control);
+			kfree_skb(skb);
+			break;
+		}
+	}
+}
+
+static int llc_shdlc_w_used(int ns, int dnr)
+{
+	int unack_count;
+
+	if (dnr <= ns)
+		unack_count = ns - dnr;
+	else
+		unack_count = 8 - dnr + ns;
+
+	return unack_count;
+}
+
+/* Send frames according to algorithm at spec:10.8.1 */
+static void llc_shdlc_handle_send_queue(struct llc_shdlc *shdlc)
+{
+	struct sk_buff *skb;
+	int r;
+	unsigned long time_sent;
+
+	if (shdlc->send_q.qlen)
+		pr_debug
+		    ("sendQlen=%d ns=%d dnr=%d rnr=%s w_room=%d unackQlen=%d\n",
+		     shdlc->send_q.qlen, shdlc->ns, shdlc->dnr,
+		     shdlc->rnr == false ? "false" : "true",
+		     shdlc->w - llc_shdlc_w_used(shdlc->ns, shdlc->dnr),
+		     shdlc->ack_pending_q.qlen);
+
+	while (shdlc->send_q.qlen && shdlc->ack_pending_q.qlen < shdlc->w &&
+	       (shdlc->rnr == false)) {
+
+		if (shdlc->t1_active) {
+			del_timer_sync(&shdlc->t1_timer);
+			shdlc->t1_active = false;
+			pr_debug("Stopped T1(send ack)\n");
+		}
+
+		skb = skb_dequeue(&shdlc->send_q);
+
+		*skb_push(skb, 1) = SHDLC_CONTROL_HEAD_I | (shdlc->ns << 3) |
+				    shdlc->nr;
+
+		pr_debug("Sending I-Frame %d, waiting to rcv %d\n", shdlc->ns,
+			 shdlc->nr);
+	/*	SHDLC_DUMP_SKB("shdlc frame written", skb); */
+
+		r = shdlc->xmit_to_drv(shdlc->hdev, skb);
+		if (r < 0) {
+			shdlc->hard_fault = r;
+			break;
+		}
+
+		shdlc->ns = (shdlc->ns + 1) % 8;
+
+		time_sent = jiffies;
+		*(unsigned long *)skb->cb = time_sent;
+
+		skb_queue_tail(&shdlc->ack_pending_q, skb);
+
+		if (shdlc->t2_active == false) {
+			shdlc->t2_active = true;
+			mod_timer(&shdlc->t2_timer, time_sent +
+				  msecs_to_jiffies(SHDLC_T2_VALUE_MS));
+			pr_debug("Started T2 (retransmit)\n");
+		}
+	}
+}
+
+static void llc_shdlc_connect_timeout(unsigned long data)
+{
+	struct llc_shdlc *shdlc = (struct llc_shdlc *)data;
+
+	pr_debug("\n");
+
+	queue_work(system_nrt_wq, &shdlc->sm_work);
+}
+
+static void llc_shdlc_t1_timeout(unsigned long data)
+{
+	struct llc_shdlc *shdlc = (struct llc_shdlc *)data;
+
+	pr_debug("SoftIRQ: need to send ack\n");
+
+	queue_work(system_nrt_wq, &shdlc->sm_work);
+}
+
+static void llc_shdlc_t2_timeout(unsigned long data)
+{
+	struct llc_shdlc *shdlc = (struct llc_shdlc *)data;
+
+	pr_debug("SoftIRQ: need to retransmit\n");
+
+	queue_work(system_nrt_wq, &shdlc->sm_work);
+}
+
+static void llc_shdlc_sm_work(struct work_struct *work)
+{
+	struct llc_shdlc *shdlc = container_of(work, struct llc_shdlc, sm_work);
+	int r;
+
+	pr_debug("\n");
+
+	mutex_lock(&shdlc->state_mutex);
+
+	switch (shdlc->state) {
+	case SHDLC_DISCONNECTED:
+		skb_queue_purge(&shdlc->rcv_q);
+		skb_queue_purge(&shdlc->send_q);
+		skb_queue_purge(&shdlc->ack_pending_q);
+		break;
+	case SHDLC_CONNECTING:
+		if (shdlc->hard_fault) {
+			llc_shdlc_connect_complete(shdlc, shdlc->hard_fault);
+			break;
+		}
+
+		if (shdlc->connect_tries++ < 5)
+			r = llc_shdlc_connect_initiate(shdlc);
+		else
+			r = -ETIME;
+		if (r < 0)
+			llc_shdlc_connect_complete(shdlc, r);
+		else {
+			mod_timer(&shdlc->connect_timer, jiffies +
+				  msecs_to_jiffies(SHDLC_CONNECT_VALUE_MS));
+
+			shdlc->state = SHDLC_NEGOCIATING;
+		}
+		break;
+	case SHDLC_NEGOCIATING:
+		if (timer_pending(&shdlc->connect_timer) == 0) {
+			shdlc->state = SHDLC_CONNECTING;
+			queue_work(system_nrt_wq, &shdlc->sm_work);
+		}
+
+		llc_shdlc_handle_rcv_queue(shdlc);
+
+		if (shdlc->hard_fault) {
+			llc_shdlc_connect_complete(shdlc, shdlc->hard_fault);
+			break;
+		}
+		break;
+	case SHDLC_CONNECTED:
+		llc_shdlc_handle_rcv_queue(shdlc);
+		llc_shdlc_handle_send_queue(shdlc);
+
+		if (shdlc->t1_active && timer_pending(&shdlc->t1_timer) == 0) {
+			pr_debug
+			    ("Handle T1(send ack) elapsed (T1 now inactive)\n");
+
+			shdlc->t1_active = false;
+			r = llc_shdlc_send_s_frame(shdlc, S_FRAME_RR,
+						   shdlc->nr);
+			if (r < 0)
+				shdlc->hard_fault = r;
+		}
+
+		if (shdlc->t2_active && timer_pending(&shdlc->t2_timer) == 0) {
+			pr_debug
+			    ("Handle T2(retransmit) elapsed (T2 inactive)\n");
+
+			shdlc->t2_active = false;
+
+			llc_shdlc_requeue_ack_pending(shdlc);
+			llc_shdlc_handle_send_queue(shdlc);
+		}
+
+		if (shdlc->hard_fault) {
+			shdlc->llc_failure(shdlc->hdev, shdlc->hard_fault);
+		}
+		break;
+	default:
+		break;
+	}
+	mutex_unlock(&shdlc->state_mutex);
+}
+
+/*
+ * Called from syscall context to establish shdlc link. Sleeps until
+ * link is ready or failure.
+ */
+static int llc_shdlc_connect(struct llc_shdlc *shdlc)
+{
+	DECLARE_WAIT_QUEUE_HEAD_ONSTACK(connect_wq);
+
+	pr_debug("\n");
+
+	mutex_lock(&shdlc->state_mutex);
+
+	shdlc->state = SHDLC_CONNECTING;
+	shdlc->connect_wq = &connect_wq;
+	shdlc->connect_tries = 0;
+	shdlc->connect_result = 1;
+
+	mutex_unlock(&shdlc->state_mutex);
+
+	queue_work(system_nrt_wq, &shdlc->sm_work);
+
+	wait_event(connect_wq, shdlc->connect_result != 1);
+
+	return shdlc->connect_result;
+}
+
+static void llc_shdlc_disconnect(struct llc_shdlc *shdlc)
+{
+	pr_debug("\n");
+
+	mutex_lock(&shdlc->state_mutex);
+
+	shdlc->state = SHDLC_DISCONNECTED;
+
+	mutex_unlock(&shdlc->state_mutex);
+
+	queue_work(system_nrt_wq, &shdlc->sm_work);
+}
+
+/*
+ * Receive an incoming shdlc frame. Frame has already been crc-validated.
+ * skb contains only LLC header and payload.
+ * If skb == NULL, it is a notification that the link below is dead.
+ */
+static void llc_shdlc_recv_frame(struct llc_shdlc *shdlc, struct sk_buff *skb)
+{
+	if (skb == NULL) {
+		pr_err("NULL Frame -> link is dead\n");
+		shdlc->hard_fault = -EREMOTEIO;
+	} else {
+		SHDLC_DUMP_SKB("incoming frame", skb);
+		skb_queue_tail(&shdlc->rcv_q, skb);
+	}
+
+	queue_work(system_nrt_wq, &shdlc->sm_work);
+}
+
+static void *llc_shdlc_init(struct nfc_hci_dev *hdev, xmit_to_drv_t xmit_to_drv,
+			    rcv_to_hci_t rcv_to_hci, int tx_headroom,
+			    int tx_tailroom, int *rx_headroom, int *rx_tailroom,
+			    llc_failure_t llc_failure)
+{
+	struct llc_shdlc *shdlc;
+
+	*rx_headroom = SHDLC_LLC_HEAD_ROOM;
+	*rx_tailroom = 0;
+
+	shdlc = kzalloc(sizeof(struct llc_shdlc), GFP_KERNEL);
+	if (shdlc == NULL)
+		return NULL;
+
+	mutex_init(&shdlc->state_mutex);
+	shdlc->state = SHDLC_DISCONNECTED;
+
+	init_timer(&shdlc->connect_timer);
+	shdlc->connect_timer.data = (unsigned long)shdlc;
+	shdlc->connect_timer.function = llc_shdlc_connect_timeout;
+
+	init_timer(&shdlc->t1_timer);
+	shdlc->t1_timer.data = (unsigned long)shdlc;
+	shdlc->t1_timer.function = llc_shdlc_t1_timeout;
+
+	init_timer(&shdlc->t2_timer);
+	shdlc->t2_timer.data = (unsigned long)shdlc;
+	shdlc->t2_timer.function = llc_shdlc_t2_timeout;
+
+	shdlc->w = SHDLC_MAX_WINDOW;
+	shdlc->srej_support = SHDLC_SREJ_SUPPORT;
+
+	skb_queue_head_init(&shdlc->rcv_q);
+	skb_queue_head_init(&shdlc->send_q);
+	skb_queue_head_init(&shdlc->ack_pending_q);
+
+	INIT_WORK(&shdlc->sm_work, llc_shdlc_sm_work);
+
+	shdlc->hdev = hdev;
+	shdlc->xmit_to_drv = xmit_to_drv;
+	shdlc->rcv_to_hci = rcv_to_hci;
+	shdlc->tx_headroom = tx_headroom;
+	shdlc->tx_tailroom = tx_tailroom;
+	shdlc->llc_failure = llc_failure;
+
+	return shdlc;
+}
+
+static void llc_shdlc_deinit(struct nfc_llc *llc)
+{
+	struct llc_shdlc *shdlc = nfc_llc_get_data(llc);
+
+	skb_queue_purge(&shdlc->rcv_q);
+	skb_queue_purge(&shdlc->send_q);
+	skb_queue_purge(&shdlc->ack_pending_q);
+
+	kfree(shdlc);
+}
+
+static int llc_shdlc_start(struct nfc_llc *llc)
+{
+	struct llc_shdlc *shdlc = nfc_llc_get_data(llc);
+
+	return llc_shdlc_connect(shdlc);
+}
+
+static int llc_shdlc_stop(struct nfc_llc *llc)
+{
+	struct llc_shdlc *shdlc = nfc_llc_get_data(llc);
+
+	llc_shdlc_disconnect(shdlc);
+
+	return 0;
+}
+
+static void llc_shdlc_rcv_from_drv(struct nfc_llc *llc, struct sk_buff *skb)
+{
+	struct llc_shdlc *shdlc = nfc_llc_get_data(llc);
+
+	llc_shdlc_recv_frame(shdlc, skb);
+}
+
+static int llc_shdlc_xmit_from_hci(struct nfc_llc *llc, struct sk_buff *skb)
+{
+	struct llc_shdlc *shdlc = nfc_llc_get_data(llc);
+
+	skb_queue_tail(&shdlc->send_q, skb);
+
+	queue_work(system_nrt_wq, &shdlc->sm_work);
+
+	return 0;
+}
+
+static struct nfc_llc_ops llc_shdlc_ops = {
+	.init = llc_shdlc_init,
+	.deinit = llc_shdlc_deinit,
+	.start = llc_shdlc_start,
+	.stop = llc_shdlc_stop,
+	.rcv_from_drv = llc_shdlc_rcv_from_drv,
+	.xmit_from_hci = llc_shdlc_xmit_from_hci,
+};
+
+int nfc_llc_shdlc_register()
+{
+	return nfc_llc_register(LLC_SHDLC_NAME, &llc_shdlc_ops);
+}
+EXPORT_SYMBOL(nfc_llc_shdlc_register);