path: root/net/nfc/hci/shdlc.c

/*
 * Copyright (C) 2012  Intel Corporation. All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * 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/sched.h>
#include <linux/export.h>
#include <linux/wait.h>
#include <linux/crc-ccitt.h>
#include <linux/slab.h>
#include <linux/skbuff.h>

#include <net/nfc/hci.h>
#include <net/nfc/shdlc.h>

#define SHDLC_LLC_HEAD_ROOM	2
#define SHDLC_LLC_TAIL_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 nfc_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 nfc_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 *nfc_shdlc_alloc_skb(struct nfc_shdlc *shdlc,
					   int payload_len)
{
	struct sk_buff *skb;

	skb = alloc_skb(shdlc->client_headroom + SHDLC_LLC_HEAD_ROOM +
			shdlc->client_tailroom + SHDLC_LLC_TAIL_ROOM +
			payload_len, GFP_KERNEL);
	if (skb)
		skb_reserve(skb, shdlc->client_headroom + SHDLC_LLC_HEAD_ROOM);

	return skb;
}

static void nfc_shdlc_add_len_crc(struct sk_buff *skb)
{
	u16 crc;
	int len;

	len = skb->len + 2;
	*skb_push(skb, 1) = len;

	crc = crc_ccitt(0xffff, skb->data, skb->len);
	crc = ~crc;
	*skb_put(skb, 1) = crc & 0xff;
	*skb_put(skb, 1) = crc >> 8;
}

/* immediately sends an S frame. */
static int nfc_shdlc_send_s_frame(struct nfc_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 = nfc_shdlc_alloc_skb(shdlc, 0);
	if (skb == NULL)
		return -ENOMEM;

	*skb_push(skb, 1) = SHDLC_CONTROL_HEAD_S | (sframe_type << 3) | nr;

	nfc_shdlc_add_len_crc(skb);

	r = shdlc->ops->xmit(shdlc, skb);

	kfree_skb(skb);

	return r;
}

/* immediately sends an U frame. skb may contain optional payload */
static int nfc_shdlc_send_u_frame(struct nfc_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;

	nfc_shdlc_add_len_crc(skb);

	r = shdlc->ops->xmit(shdlc, 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 nfc_shdlc_reset_t2(struct nfc_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->