NFC: nci: add generic uart support

Some NFC controller supports UART as host interface.
As with SPI, a lot of code can be shared between vendor
drivers. This patch add the generic support of UART and
provides some extension API for vendor specific needs.

This code is strongly inspired by the Bluetooth HCI ldisc
implementation. NCI UART vendor drivers will have to register
themselves to this layer via nci_uart_register.

Underlying tty will have to be configured from user land
thanks to an ioctl.

Signed-off-by: Vincent Cuissard <cuissard@marvell.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

3 files changed, 505 insertions, 0 deletions

diff --git a/net/nfc/nci/Kconfig b/net/nfc/nci/Kconfig
index a4f1e42e3481..901c1ddba841 100644
--- a/net/nfc/nci/Kconfig
+++ b/net/nfc/nci/Kconfig
@@ -19,3 +19,10 @@ config NFC_NCI_SPI
 	  an NFC Controller (NFCC) and a Device Host (DH).
 
 	  Say yes if you use an NCI driver that requires SPI link layer.
+
+config NFC_NCI_UART
+	depends on NFC_NCI && TTY
+	tristate "NCI over UART protocol support"
+	default n
+	help
+	  Say yes if you use an NCI driver that requires UART link layer.
diff --git a/net/nfc/nci/Makefile b/net/nfc/nci/Makefile
index 7ed8949266cc..b4b85b82e988 100644
--- a/net/nfc/nci/Makefile
+++ b/net/nfc/nci/Makefile
@@ -7,3 +7,6 @@ obj-$(CONFIG_NFC_NCI) += nci.o
 nci-objs := core.o data.o lib.o ntf.o rsp.o hci.o
 
 nci-$(CONFIG_NFC_NCI_SPI) += spi.o
+
+nci_uart-y += uart.o
+obj-$(CONFIG_NFC_NCI_UART) += nci_uart.o
diff --git a/net/nfc/nci/uart.c b/net/nfc/nci/uart.c
new file mode 100644
index 000000000000..70c279543074
--- /dev/null
+++ b/net/nfc/nci/uart.c
@@ -0,0 +1,495 @@
+/*
+ * Copyright (C) 2015, Marvell International Ltd.
+ *
+ * This software file (the "File") is distributed by Marvell International
+ * Ltd. under the terms of the GNU General Public License Version 2, June 1991
+ * (the "License").  You may use, redistribute and/or modify this File in
+ * accordance with the terms and conditions of the License, a copy of which
+ * is available on the worldwide web at
+ * http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt.
+ *
+ * THE FILE IS DISTRIBUTED AS-IS, WITHOUT WARRANTY OF ANY KIND, AND THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
+ * ARE EXPRESSLY DISCLAIMED.  The License provides additional details about
+ * this warranty disclaimer.
+
+ */
+
+/* Inspired (hugely) by HCI LDISC implementation in Bluetooth.
+ *
+ *  Copyright (C) 2000-2001  Qualcomm Incorporated
+ *  Copyright (C) 2002-2003  Maxim Krasnyansky <maxk@qualcomm.com>
+ *  Copyright (C) 2004-2005  Marcel Holtmann <marcel@holtmann.org>
+ */
+
+#include <linux/module.h>
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/types.h>
+#include <linux/fcntl.h>
+#include <linux/interrupt.h>
+#include <linux/ptrace.h>
+#include <linux/poll.h>
+
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/signal.h>
+#include <linux/ioctl.h>
+#include <linux/skbuff.h>
+
+#include <net/nfc/nci.h>
+#include <net/nfc/nci_core.h>
+
+/* TX states  */
+#define NCI_UART_SENDING	1
+#define NCI_UART_TX_WAKEUP	2
+
+static struct nci_uart *nci_uart_drivers[NCI_UART_DRIVER_MAX];
+
+static inline struct sk_buff *nci_uart_dequeue(struct nci_uart *nu)
+{
+	struct sk_buff *skb = nu->tx_skb;
+
+	if (!skb)
+		skb = skb_dequeue(&nu->tx_q);
+	else
+		nu->tx_skb = NULL;
+
+	return skb;
+}
+
+static inline int nci_uart_queue_empty(struct nci_uart *nu)
+{
+	if (nu->tx_skb)
+		return 0;
+
+	return skb_queue_empty(&nu->tx_q);
+}
+
+static int nci_uart_tx_wakeup(struct nci_uart *nu)
+{
+	if (test_and_set_bit(NCI_UART_SENDING, &nu->tx_state)) {
+		set_bit(NCI_UART_TX_WAKEUP, &nu->tx_state);
+		return 0;
+	}
+
+	schedule_work(&nu->write_work);
+
+	return 0;
+}
+
+static void nci_uart_write_work(struct work_struct *work)
+{
+	struct nci_uart *nu = container_of(work, struct nci_uart, write_work);
+	struct tty_struct *tty = nu->tty;
+	struct sk_buff *skb;
+
+restart:
+	clear_bit(NCI_UART_TX_WAKEUP, &nu->tx_state);
+
+	if (nu->ops.tx_start)
+		nu->ops.tx_start(nu);
+
+	while ((skb = nci_uart_dequeue(nu))) {
+		int len;
+
+		set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
+		len = tty->ops->write(tty, skb->data, skb->len);
+		skb_pull(skb, len);
+		if (skb->len) {
+			nu->tx_skb = skb;
+			break;
+		}
+		kfree_skb(skb);
+	}
+
+	if (test_bit(NCI_UART_TX_WAKEUP, &nu->tx_state))
+		goto restart;
+
+	if (nu->ops.tx_done && nci_uart_queue_empty(nu))
+		nu->ops.tx_done(nu);
+
+	clear_bit(NCI_UART_SENDING, &nu->tx_state);
+}
+
+static int nci_uart_set_driver(struct tty_struct *tty, unsigned int driver)
+{
+	struct nci_uart *nu = NULL;
+	int ret;
+
+	if (driver >= NCI_UART_DRIVER_MAX)
+		return -EINVAL;
+
+	if (!nci_uart_drivers[driver])
+		return -ENOENT;
+
+	nu = kzalloc(sizeof(*nu), GFP_KERNEL);
+	if (!nu)
+		return -ENOMEM;
+
+	memcpy(nu, nci_uart_drivers[driver], sizeof(struct nci_uart));
+	nu->tty = tty;
+	tty->disc_data = nu;
+	skb_queue_head_init(&nu->tx_q);
+	INIT_WORK(&nu->write_work, nci_uart_write_work);
+	spin_lock_init(&nu->rx_lock);
+
+	ret = nu->ops.open(nu);
+	if (ret) {
+		tty->disc_data = NULL;
+		kfree(nu);
+	} else if (!try_module_get(nu->owner)) {
+		nu->ops.close(nu);
+		tty->disc_data = NULL;
+		kfree(nu);
+		return -ENOENT;
+	}
+	return ret;
+}
+
+/* ------ LDISC part ------ */
+
+/* nci_uart_tty_open
+ *
+ *     Called when line discipline changed to NCI_UART.
+ *
+ * Arguments:
+ *     tty    pointer to tty info structure
+ * Return Value:
+ *     0 if success, otherwise error code
+ */
+static int nci_uart_tty_open(struct tty_struct *tty)
+{
+	/* Error if the tty has no write op instead of leaving an exploitable
+	 * hole
+	 */
+	if (!tty->ops->write)
+		return -EOPNOTSUPP;
+
+	tty->disc_data = NULL;
+	tty->receive_room = 65536;
+
+	/* Flush any pending characters in the driver and line discipline. */
+
+	/* FIXME: why is this needed. Note don't use ldisc_ref here as the
+	 * open path is before the ldisc is referencable.
+	 */
+
+	if (tty->ldisc->ops->flush_buffer)
+		tty->ldisc->ops->flush_buffer(tty);
+	tty_driver_flush_buffer(tty);
+
+	return 0;
+}
+
+/* nci_uart_tty_close()
+ *
+ *    Called when the line discipline is changed to something
+ *    else, the tty is closed, or the tty detects a hangup.
+ */
+static void nci_uart_tty_close(struct tty_struct *tty)
+{
+	struct nci_uart *nu = (void *)tty->disc_data;
+
+	/* Detach from the tty */
+	tty->disc_data = NULL;
+
+	if (!nu)
+		return;
+
+	if (nu->tx_skb)
+		kfree_skb(nu->tx_skb);
+	if (nu->rx_skb)
+		kfree_skb(nu->rx_skb);
+
+	skb_queue_purge(&nu->tx_q);
+
+	nu->ops.close(nu);
+	nu->tty = NULL;
+	module_put(nu->owner);
+
+	cancel_work_sync(&nu->write_work);
+
+	kfree(nu);
+}
+
+/* nci_uart_tty_wakeup()
+ *
+ *    Callback for transmit wakeup. Called when low level
+ *    device driver can accept more send data.
+ *
+ * Arguments:        tty    pointer to associated tty instance data
+ * Return Value:    None
+ */
+static void nci_uart_tty_wakeup(struct tty_struct *tty)
+{
+	struct nci_uart *nu = (void *)tty->disc_data;
+
+	if (!nu)
+		return;
+
+	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
+
+	if (tty != nu->tty)
+		return;
+
+	nci_uart_tx_wakeup(nu);
+}
+
+/* nci_uart_tty_receive()
+ *
+ *     Called by tty low level driver when receive data is
+ *     available.
+ *
+ * Arguments:  tty          pointer to tty isntance data
+ *             data         pointer to received data
+ *             flags        pointer to flags for data
+ *             count        count of received data in bytes
+ *
+ * Return Value:    None
+ */
+static void nci_uart_tty_receive(struct tty_struct *tty, const u8 *data,
+				 char *flags, int count)
+{
+	struct nci_uart *nu = (void *)tty->disc_data;
+
+	if (!nu || tty != nu->tty)
+		return;
+
+	spin_lock(&nu->rx_lock);
+	nu->ops.recv_buf(nu, (void *)data, flags, count);
+	spin_unlock(&nu->rx_lock);
+
+	tty_unthrottle(tty);
+}
+
+/* nci_uart_tty_ioctl()
+ *
+ *    Process IOCTL system call for the tty device.
+ *
+ * Arguments:
+ *
+ *    tty        pointer to tty instance data
+ *    file       pointer to open file object for device
+ *    cmd        IOCTL command code
+ *    arg        argument for IOCTL call (cmd dependent)
+ *
+ * Return Value:    Command dependent
+ */
+static int nci_uart_tty_ioctl(struct tty_struct *tty, struct file *file,
+			      unsigned int cmd, unsigned long arg)
+{
+	struct nci_uart *nu = (void *)tty->disc_data;
+	int err = 0;
+
+	switch (cmd) {
+	case NCIUARTSETDRIVER:
+		if (!nu)
+			return nci_uart_set_driver(tty, (unsigned int)arg);
+		else
+			return -EBUSY;
+		break;
+	default:
+		err = n_tty_ioctl_helper(tty, file, cmd, arg);
+		break;
+	}
+
+	return err;
+}
+
+/* We don't provide read/write/poll interface for user space. */
+static ssize_t nci_uart_tty_read(struct tty_struct *tty, struct file *file,
+				 unsigned char __user *buf, size_t nr)
+{
+	return 0;
+}
+
+static ssize_t nci_uart_tty_write(struct tty_struct *tty, struct file *file,
+				  const unsigned char *data, size_t count)
+{
+	return 0;
+}
+
+static unsigned int nci_uart_tty_poll(struct tty_struct *tty,
+				      struct file *filp, poll_table *wait)
+{
+	return 0;
+}
+
+static int nci_uart_send(struct nci_uart *nu, struct sk_buff *skb)
+{
+	/* Queue TX packet */
+	skb_queue_tail(&nu->tx_q, skb);
+
+	/* Try to start TX (if possible) */
+	nci_uart_tx_wakeup(nu);
+
+	return 0;
+}
+
+/* -- Default recv_buf handler --
+ *
+ * This handler supposes that NCI frames are sent over UART link without any
+ * framing. It reads NCI header, retrieve the packet size and once all packet
+ * bytes are received it passes it to nci_uart driver for processing.
+ */
+static int nci_uart_default_recv_buf(struct nci_uart *nu, const u8 *data,
+				     char *flags, int count)
+{
+	int chunk_len;
+
+	if (!nu->ndev) {
+		nfc_err(nu->tty->dev,
+			"receive data from tty but no NCI dev is attached yet, drop buffer\n");
+		return 0;
+	}
+
+	/* Decode all incoming data in packets
+	 * and enqueue then for processing.
+	 */
+	while (count > 0) {
+		/* If this is the first data of a packet, allocate a buffer */
+		if (!nu->rx_skb) {
+			nu->rx_packet_len = -1;
+			nu->rx_skb = nci_skb_alloc(nu->ndev,
+						   NCI_MAX_PACKET_SIZE,
+						   GFP_KERNEL);
+			if (!nu->rx_skb)
+				return -ENOMEM;
+		}
+
+		/* Eat byte after byte till full packet header is received */
+		if (nu->rx_skb->len < NCI_CTRL_HDR_SIZE) {
+			*skb_put(nu->rx_skb, 1) = *data++;
+			--count;
+			continue;
+		}
+
+		/* Header was received but packet len was not read */
+		if (nu->rx_packet_len < 0)
+			nu->rx_packet_len = NCI_CTRL_HDR_SIZE +
+				nci_plen(nu->rx_skb->data);
+
+		/* Compute how many bytes are missing and how many bytes can
+		 * be consumed.
+		 */
+		chunk_len = nu->rx_packet_len - nu->rx_skb->len;
+		if (count < chunk_len)
+			chunk_len = count;
+		memcpy(skb_put(nu->rx_skb, chunk_len), data, chunk_len);
+		data += chunk_len;
+		count -= chunk_len;
+
+		/* Chcek if packet is fully received */
+		if (nu->rx_packet_len == nu->rx_skb->len) {
+			/* Pass RX packet to driver */
+			if (nu->ops.recv(nu, nu->rx_skb) != 0)
+				nfc_err(nu->tty->dev, "corrupted RX packet\n");
+			/* Next packet will be a new one */
+			nu->rx_skb = NULL;
+		}
+	}
+
+	return 0;
+}
+
+/* -- Default recv handler -- */
+static int nci_uart_default_recv(struct nci_uart *nu, struct sk_buff *skb)
+{
+	return nci_recv_frame(nu->ndev, skb);
+}
+
+int nci_uart_register(struct nci_uart *nu)
+{
+	if (!nu || !nu->ops.open ||
+	    !nu->ops.recv || !nu->ops.close)
+		return -EINVAL;
+
+	/* Set the send callback */
+	nu->ops.send = nci_uart_send;
+
+	/* Install default handlers if not overridden */
+	if (!nu->ops.recv_buf)
+		nu->ops.recv_buf = nci_uart_default_recv_buf;
+	if (!nu->ops.recv)
+		nu->ops.recv = nci_uart_default_recv;
+
+	/* Add this driver in the driver list */
+	if (!nci_uart_drivers[nu->driver]) {
+		pr_err("driver %d is already registered\n", nu->driver);
+		return -EBUSY;
+	}
+	nci_uart_drivers[nu->driver] = nu;
+
+	pr_info("NCI uart driver '%s [%d]' registered\n", nu->name, nu->driver);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(nci_uart_register);
+
+void nci_uart_unregister(struct nci_uart *nu)
+{
+	pr_info("NCI uart driver '%s [%d]' unregistered\n", nu->name,
+		nu->driver);
+
+	/* Remove this driver from the driver list */
+	nci_uart_drivers[nu->driver] = NULL;
+}
+EXPORT_SYMBOL_GPL(nci_uart_unregister);
+
+void nci_uart_set_config(struct nci_uart *nu, int baudrate, int flow_ctrl)
+{
+	struct ktermios new_termios;
+
+	if (!nu->tty)
+		return;
+
+	down_read(&nu->tty->termios_rwsem);
+	new_termios = nu->tty->termios;
+	up_read(&nu->tty->termios_rwsem);
+	tty_termios_encode_baud_rate(&new_termios, baudrate, baudrate);
+
+	if (flow_ctrl)
+		new_termios.c_cflag |= CRTSCTS;
+	else
+		new_termios.c_cflag &= ~CRTSCTS;
+
+	tty_set_termios(nu->tty, &new_termios);
+}
+EXPORT_SYMBOL_GPL(nci_uart_set_config);
+
+static struct tty_ldisc_ops nci_uart_ldisc = {
+	.magic		= TTY_LDISC_MAGIC,
+	.owner		= THIS_MODULE,
+	.name		= "n_nci",
+	.open		= nci_uart_tty_open,
+	.close		= nci_uart_tty_close,
+	.read		= nci_uart_tty_read,
+	.write		= nci_uart_tty_write,
+	.poll		= nci_uart_tty_poll,
+	.receive_buf	= nci_uart_tty_receive,
+	.write_wakeup	= nci_uart_tty_wakeup,
+	.ioctl		= nci_uart_tty_ioctl,
+};
+
+static int __init nci_uart_init(void)
+{
+	memset(nci_uart_drivers, 0, sizeof(nci_uart_drivers));
+	return tty_register_ldisc(N_NCI, &nci_uart_ldisc);
+}
+
+static void __exit nci_uart_exit(void)
+{
+	tty_unregister_ldisc(N_NCI);
+}
+
+module_init(nci_uart_init);
+module_exit(nci_uart_exit);
+
+MODULE_AUTHOR("Marvell International Ltd.");
+MODULE_DESCRIPTION("NFC NCI UART driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_LDISC(N_NCI);