[PATCH v5] serial: spi: add spi-uart driver for Maxim 3110

[Feng Tang <feng.tang@intel.com>]

Hi All,

Here is a driver for Maxim 3110 SPI-UART device, please help to review.

It has been validated with Designware SPI controller (drivers/spi: dw_spi.c &
dw_spi_pci.c). It supports polling and IRQ mode, supports batch read, and
provides a console.

change log:
 since v4:
        * Add explanation why not using DMA
        * Fix a bug in max3110_read_multi()
 since v3:
        * Remove the Designware controller related stuff
        * Remove some initialization code which should be done in the platform
          setup code
        * Add a missing change for drivers/serial/Makefile
 since v2:
        * Address comments from Andrew Morton
        * Use test/set_bit to avoid race condition for SMP/preempt case
        * Fix bug related with endian order
 since v1:
        * Address comments from Alan Cox
        * Use a "use_irq" module parameter to runtime check whether
          to use IRQ mode
        * Add the suspend/resume implementation

Thanks!
Feng


>From 6ea4918365f5eed04f82544f0da3efe93cb2cc20 Mon Sep 17 00:00:00 2001
From: Feng Tang <feng.tang@intel.com>
Date: Fri, 26 Feb 2010 11:37:29 +0800
Subject: [PATCH] serial: spi: add spi-uart driver for Maxim 3110

This is the driver for Max3110 SPI-UART device, which connect
to host with SPI interface. It supports baud rates from 300 to
230400, and supports both polling and IRQ mode, as well as
providing a console for system use

Its datasheet could be found here:
http://datasheets.maxim-ic.com/en/ds/MAX3110E-MAX3111E.pdf

Signed-off-by: Feng Tang <feng.tang@intel.com>
Cc: David Brownell <david-b@pacbell.net>
Cc: Greg KH <greg@kroah.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
---
 drivers/serial/Kconfig      |    8 +
 drivers/serial/Makefile     |    1 +
 drivers/serial/max3110.c    |  875 +++++++++++++++++++++++++++++++++++++++++++
 drivers/serial/max3110.h    |   61 +++
 include/linux/serial_core.h |    3 +
 5 files changed, 948 insertions(+), 0 deletions(-)
 create mode 100644 drivers/serial/max3110.c
 create mode 100644 drivers/serial/max3110.h

diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index 9ff47db..94aa282 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -688,6 +688,14 @@ config SERIAL_SA1100_CONSOLE
 	  your boot loader (lilo or loadlin) about how to pass options to the
 	  kernel at boot time.)
 
+config SERIAL_MAX3110
+	tristate "SPI UART driver for Max3110"
+	depends on SPI_MASTER
+	select SERIAL_CORE
+	select SERIAL_CORE_CONSOLE
+	help
+	  This is the UART protocol driver for MAX3110 device
+
 config SERIAL_BFIN
 	tristate "Blackfin serial port support"
 	depends on BLACKFIN
diff --git a/drivers/serial/Makefile b/drivers/serial/Makefile
index 5548fe7..b93d8a0 100644
--- a/drivers/serial/Makefile
+++ b/drivers/serial/Makefile
@@ -46,6 +46,7 @@ obj-$(CONFIG_SERIAL_S3C24A0) += s3c24a0.o
 obj-$(CONFIG_SERIAL_S3C6400) += s3c6400.o
 obj-$(CONFIG_SERIAL_S5PC100) += s3c6400.o
 obj-$(CONFIG_SERIAL_MAX3100) += max3100.o
+obj-$(CONFIG_SERIAL_MAX3110) += max3110.o
 obj-$(CONFIG_SERIAL_IP22_ZILOG) += ip22zilog.o
 obj-$(CONFIG_SERIAL_MUX) += mux.o
 obj-$(CONFIG_SERIAL_68328) += 68328serial.o
diff --git a/drivers/serial/max3110.c b/drivers/serial/max3110.c
new file mode 100644
index 0000000..aff0465
--- /dev/null
+++ b/drivers/serial/max3110.c
@@ -0,0 +1,875 @@
+/*
+ * max3110.c - spi uart protocol driver for Maxim 3110
+ *
+ * Copyright (c) 2009, Intel Corporation.
+ *
+ * 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 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.,
+ * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+/*
+ * Note:
+ * 1. From Max3110 spec, the Rx FIFO has 8 words, while the Tx FIFO only has
+ *    1 word. If SPI master controller doesn't support sclk frequency change,
+ *    then the char need be sent out one by one with some delay
+ *
+ * 2. Currently only RX availabe interrrupt is used
+ *
+ * 3. This driver doesn't support work with a spi cotnroller in DMA mode, and
+ *    the reason for not using DMA is:
+ *    a) Maxim 3110 is a low speed UART device, whose tx/rx buffer are very few,
+ *    and using DMA may be over-killing when working as a system console(imaging
+ *    we edit a text file on it)
+ *    b) Handling only one 16b word transfer will be very common, but non-32b
+ *    aligned DMA operation is not supported by all kinds of DMA controllers
+ *
+ *    Some spi controller drivers like Pxa2xx, Designware have option for device
+ *    driver to chose to work in poll or DMA mode. And platform driver which
+ *    enumerates Max3110 device should leverage this option to not use DMA.
+ */
+
+#include <linux/module.h>
+#include <linux/ioport.h>
+#include <linux/init.h>
+#include <linux/console.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/serial_core.h>
+#include <linux/serial_reg.h>
+
+#include <linux/kthread.h>
+#include <linux/delay.h>
+#include <linux/spi/spi.h>
+
+#include "max3110.h"
+
+#define PR_FMT	"max3110: "
+
+struct uart_max3110 {
+	struct uart_port port;
+	struct spi_device *spi;
+	char *name;
+
+	wait_queue_head_t wq;
+	struct task_struct *main_thread;
+	struct task_struct *read_thread;
+	spinlock_t lock;
+
+	u32 baud;
+	u16 cur_conf;
+	u8 clock;
+	u8 parity, word_7bits;
+	u16 irq;
+
+	/* bit map for UART status */
+	unsigned long flags;
+#define M3110_CON_TX_NEED	0
+#define M3110_UART_TX_NEED	1
+#define M3110_IRQ_PENDING	2
+	unsigned long mthread_up;
+
+	/* console buffer */
+	struct circ_buf con_xmit;
+};
+
+static struct uart_max3110 *pmax;
+
+static int use_irq = 1;
+module_param(use_irq, int, 0444);
+MODULE_PARM_DESC(use_irq, "Whether using Max3110's IRQ capability");
+
+static void receive_chars(struct uart_max3110 *max,
+				unsigned char *str, int len);
+static int max3110_read_multi(struct uart_max3110 *max, u8 *buf);
+static void max3110_con_receive(struct uart_max3110 *max);
+
+static int max3110_write_then_read(struct uart_max3110 *max,
+		const void *txbuf, void *rxbuf, unsigned len, int always_fast)
+{
+	struct spi_device *spi = max->spi;
+	struct spi_message	message;
+	struct spi_transfer	x;
+	int ret;
+
+	spi_message_init(&message);
+	memset(&x, 0, sizeof x);
+	x.len = len;
+	x.tx_buf = txbuf;
+	x.rx_buf = rxbuf;
+	spi_message_add_tail(&x, &message);
+
+	if (always_fast)
+		x.speed_hz = spi->max_speed_hz;
+	else if (max->baud)
+		x.speed_hz = max->baud;
+
+	/* Do the i/o */
+	ret = spi_sync(spi, &message);
+	return ret;
+}
+
+/* Write a u16 to the device, and return one u16 read back */
+static int max3110_out(struct uart_max3110 *max, const u16 out)
+{
+	u16 tmp;
+	u8  ch;
+	int ret;
+
+	ret = max3110_write_then_read(max, &out, &tmp, 2, 1);
+	if (ret) {
+		pr_warning(PR_FMT "%s(): get err msg %d when sending 0x%x\n",
+				__func__, ret, out);
+		return ret;
+	}
+
+	/* If some valid data is read back */
+	if (tmp & MAX3110_READ_DATA_AVAILABLE) {
+		ch = tmp & 0xff;
+		receive_chars(max, &ch, 1);
+	}
+
+	return ret;
+}
+
+/*
+ * This is usually used to read data from SPIC RX FIFO, which doesn't
+ * need any delay like flushing character out.
+ *
+ * Return how many valide bytes are read back
+ */
+static int max3110_read_multi(struct uart_max3110 *max, u8 *buf)
+{
+	u16 obuf[M3110_RX_FIFO_DEPTH], ibuf[M3110_RX_FIFO_DEPTH];
+	u8 *pbuf, valid_str[M3110_RX_FIFO_DEPTH];
+	int i, j, blen;
+
+	/* tx/rx always have the same length */
+	blen = sizeof(obuf);
+	memset(obuf, 0, blen);
+	memset(ibuf, 0, blen);
+
+	if (max3110_write_then_read(max, obuf, ibuf, blen, 1))
+		return 0;
+
+	/* If caller doesn't provide a buffer, then handle received char */
+	pbuf = buf ? buf : valid_str;
+
+	for (i = 0, j = 0; i < M3110_RX_FIFO_DEPTH; i++) {
+		if (ibuf[i] & MAX3110_READ_DATA_AVAILABLE)
+			pbuf[j++] = ibuf[i] & 0xff;
+	}
+
+	if (j && (pbuf == valid_str))
+		receive_chars(max, valid_str, j);
+
+	return j;
+}
+
+static void serial_m3110_con_putchar(struct uart_port *port, int ch)
+{
+	struct uart_max3110 *max =
+		container_of(port, struct uart_max3110, port);
+	struct circ_buf *xmit = &max->con_xmit;
+
+	if (uart_circ_chars_free(xmit)) {
+		xmit->buf[xmit->head] = (char)ch;
+		xmit->head = (xmit->head + 1) & (PAGE_SIZE - 1);
+	}
+}
+
+/*
+ * Print a string to the serial port trying not to disturb
+ * any possible real use of the port...
+ *
+ *	The console_lock must be held when we get here.
+ */
+static void serial_m3110_con_write(struct console *co,
+				const char *s, unsigned int count)
+{
+	if (!pmax)
+		return;
+
+	uart_console_write(&pmax->port, s, count, serial_m3110_con_putchar);
+
+	set_bit(M3110_CON_TX_NEED, &pmax->flags);
+	if (!test_bit(0, &pmax->mthread_up))
+		wake_up_process(pmax->main_thread);
+}
+
+static int __init
+serial_m3110_con_setup(struct console *co, char *options)
+{
+	struct uart_max3110 *max = pmax;
+	int baud = 115200;
+	int bits = 8;
+	int parity = 'n';
+	int flow = 'n';
+
+	pr_info(PR_FMT "setting up console\n");
+
+	if (!max) {
+		pr_err(PR_FMT "pmax is NULL, return");
+		return -ENODEV;
+	}
+
+	if (options)
+		uart_parse_options(options, &baud, &parity, &bits, &flow);
+
+	return uart_set_options(&max->port, co, baud, parity, bits, flow);
+}
+
+static struct tty_driver *serial_m3110_con_device(struct console *co,
+							int *index)
+{
+	struct uart_driver *p = co->data;
+	*index = co->index;
+	return p->tty_driver;
+}
+
+static struct uart_driver serial_m3110_reg;
+static struct console serial_m3110_console = {
+	.name		= "ttyS",
+	.write		= serial_m3110_con_write,
+	.device		= serial_m3110_con_device,
+	.setup		= serial_m3110_con_setup,
+	.flags		= CON_PRINTBUFFER,
+	.index		= -1,
+	.data		= &serial_m3110_reg,
+};
+
+
+static unsigned int serial_m3110_tx_empty(struct uart_port *port)
+{
+	return 1;
+}
+
+static void serial_m3110_stop_tx(struct uart_port *port)
+{
+	return;
+}
+
+static void serial_m3110_stop_rx(struct uart_port *port)
+{
+	return;
+}
+
+#define WORDS_PER_XFER	128
+static void send_circ_buf(struct uart_max3110 *max,
+				struct circ_buf *xmit)
+{
+	int len, blen, left = 0;
+	u16 obuf[WORDS_PER_XFER], ibuf[WORDS_PER_XFER];
+	u8 valid_str[WORDS_PER_XFER];
+	int i, j;
+	int ret = 0;
+
+	while (!uart_circ_empty(xmit)) {
+		left = uart_circ_chars_pending(xmit);
+		while (left) {
+			len = min(left, WORDS_PER_XFER);
+			blen = len * sizeof(u16);
+			memset(obuf, 0, blen);
+			memset(ibuf, 0, blen);
+
+			for (i = 0; i < len; i++) {
+				obuf[i] = (u8)xmit->buf[xmit->tail] | WD_TAG;
+				xmit->tail = (xmit->tail + 1) &
+						(UART_XMIT_SIZE - 1);
+			}
+
+			/* Fail to send msg to console is not very critical */
+			ret = max3110_write_then_read(max, obuf, ibuf, blen, 0);
+			if (ret)
+				pr_warning(PR_FMT "%s(): get err msg %d\n",
+						__func__, ret);
+
+			for (i = 0, j = 0; i < len; i++) {
+				if (ibuf[i] & MAX3110_READ_DATA_AVAILABLE)
+					valid_str[j++] = ibuf[i] & 0xff;
+			}
+
+			if (j)
+				receive_chars(max, valid_str, j);
+
+			max->port.icount.tx += len;
+			left -= len;
+		}
+	}
+}
+
+static void transmit_char(struct uart_max3110 *max)
+{
+	struct uart_port *port = &max->port;
+	struct circ_buf *xmit = &port->state->xmit;
+
+	if (uart_circ_empty(xmit) || uart_tx_stopped(port))
+		return;
+
+	send_circ_buf(max, xmit);
+
+	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+		uart_write_wakeup(port);
+}
+
+/*
+ * This will be called by uart_write() and tty_write, can't
+ * go to sleep
+ */
+static void serial_m3110_start_tx(struct uart_port *port)
+{
+	struct uart_max3110 *max =
+		container_of(port, struct uart_max3110, port);
+
+	set_bit(M3110_UART_TX_NEED, &max->flags);
+	if (!test_bit(0, &max->mthread_up))
+		wake_up_process(max->main_thread);
+}
+
+static void receive_chars(struct uart_max3110 *max, unsigned char *str, int len)
+{
+	struct uart_port *port = &max->port;
+	struct tty_struct *tty;
+	int usable;
+
+	/* If uart is not opened, just return */
+	if (!port->state)
+		return;
+
+	tty = port->state->port.tty;
+	if (!tty)
+		return;
+
+	while (len) {
+		usable = tty_buffer_request_room(tty, len);
+		if (usable) {
+			tty_insert_flip_string(tty, str, usable);
+			str += usable;
+			port->icount.rx += usable;
+		}
+		len -= usable;
+	}
+	tty_flip_buffer_push(tty);
+}
+
+/*
+ * This routine will be used in read_thread or RX IRQ handling,
+ * it will first do one round buffer read(8 words), if there is some
+ * valid RX data, will try to read 5 more rounds till all data
+ * is read out.
+ *
+ * Use stack space as data buffer to save some system load, and chose
+ * 504 Btyes as a threadhold to do a bulk push to upper tty layer when
+ * receiving bulk data, a much bigger buffer may cause stack overflow
+ */
+static void max3110_con_receive(struct uart_max3110 *max)
+{
+	int loop = 1, num, total = 0;
+	u8 recv_buf[512], *pbuf;
+
+	pbuf = recv_buf;
+	do {
+		num = max3110_read_multi(max, pbuf);
+
+		if (num) {
+			loop = 5;
+			pbuf += num;
+			total += num;
+
+			if (total >= 504) {
+				receive_chars(max, recv_buf, total);
+				pbuf = recv_buf;
+				total = 0;
+			}
+		}
+	} while (--loop);
+
+	if (total)
+		receive_chars(max, recv_buf, total);
+}
+
+static int max3110_main_thread(void *_max)
+{
+	struct uart_max3110 *max = _max;
+	wait_queue_head_t *wq = &max->wq;
+	int ret = 0;
+	struct circ_buf *xmit = &max->con_xmit;
+
+	init_waitqueue_head(wq);
+	pr_info(PR_FMT "start main thread\n");
+
+	do {
+		wait_event_interruptible(*wq,
+				max->flags || kthread_should_stop());
+		test_and_set_bit(0, &max->mthread_up);
+
+		if (use_irq && test_bit(M3110_IRQ_PENDING, &max->flags)) {
+			max3110_con_receive(max);
+			clear_bit(M3110_IRQ_PENDING, &max->flags);
+		}
+
+		/* First handle console output */
+		if (test_bit(M3110_CON_TX_NEED, &max->flags)) {
+			send_circ_buf(max, xmit);
+			clear_bit(M3110_CON_TX_NEED, &max->flags);
+		}
+
+		/* Handle uart output */
+		if (test_bit(M3110_UART_TX_NEED, &max->flags)) {
+			transmit_char(max);
+			clear_bit(M3110_UART_TX_NEED, &max->flags);
+		}
+		test_and_clear_bit(0, &max->mthread_up);
+	} while (!kthread_should_stop());
+
+	return ret;
+}
+
+static irqreturn_t serial_m3110_irq(int irq, void *dev_id)
+{
+	struct uart_max3110 *max = dev_id;
+
+	/* max3110's irq is a falling edge, not level triggered,
+	 * so no need to disable the irq */
+	set_bit(M3110_IRQ_PENDING, &max->flags);
+
+	if (!test_bit(0, &max->mthread_up))
+		wake_up_process(max->main_thread);
+
+	return IRQ_HANDLED;
+}
+
+/* If don't use RX IRQ, then need a thread to polling read */
+static int max3110_read_thread(void *_max)
+{
+	struct uart_max3110 *max = _max;
+
+	pr_info(PR_FMT "start read thread\n");
+	do {
+		if (!test_bit(0, &max->mthread_up))
+			max3110_con_receive(max);
+
+		schedule_timeout_interruptible(HZ / 20);
+	} while (!kthread_should_stop());
+
+	return 0;
+}
+
+static int serial_m3110_startup(struct uart_port *port)
+{
+	struct uart_max3110 *max =
+		container_of(port, struct uart_max3110, port);
+	u16 config = 0;
+	int ret = 0;
+
+	if (port->line != 0) {
+		pr_err(PR_FMT "uart port startup failed\n");
+		return -1;
+	}
+
+	/* Disable all IRQ and config it to 115200, 8n1 */
+	config = WC_TAG | WC_FIFO_ENABLE
+			| WC_1_STOPBITS
+			| WC_8BIT_WORD
+			| WC_BAUD_DR2;
+
+	/* As we use thread to handle tx/rx, need set low latency */
+	port->state->port.tty->low_latency = 1;
+
+	if (use_irq) {
+		ret = request_irq(max->irq, serial_m3110_irq,
+					IRQ_TYPE_EDGE_FALLING, "max3110", max);
+		if (ret)
+			return ret;
+
+		/* Enable RX IRQ only */
+		config |= WC_RXA_IRQ_ENABLE;
+	} else {
+		/* If IRQ is disabled, start a read thread for input data */
+		max->read_thread =
+			kthread_run(max3110_read_thread, max, "max3110_read");
+		if (IS_ERR(max->read_thread)) {
+			ret = PTR_ERR(max->read_thread);
+			max->read_thread = 0;
+			pr_err(PR_FMT "Can't create read thread!");
+			return ret;
+		}
+	}
+
+	ret = max3110_out(max, config);
+	if (ret) {
+		if (use_irq)
+			free_irq(max->irq, max);
+		else
+			kthread_stop(max->read_thread);
+
+		return ret;
+	}
+
+	max->cur_conf = config;
+	return 0;
+}
+
+static void serial_m3110_shutdown(struct uart_port *port)
+{
+	struct uart_max3110 *max =
+		container_of(port, struct uart_max3110, port);
+	u16 config;
+
+	if (max->read_thread) {
+		kthread_stop(max->read_thread);
+		max->read_thread = NULL;
+	}
+
+	if (use_irq)
+		free_irq(max->irq, max);
+
+	/* Disable interrupts from this port */
+	config = WC_TAG | WC_SW_SHDI;
+	max3110_out(max, config);
+}
+
+static void serial_m3110_release_port(struct uart_port *port)
+{
+}
+
+static int serial_m3110_request_port(struct uart_port *port)
+{
+	return 0;
+}
+
+static void serial_m3110_config_port(struct uart_port *port, int flags)
+{
+	port->type = PORT_MAX3110;
+}
+
+static int
+serial_m3110_verify_port(struct uart_port *port, struct serial_struct *ser)
+{
+	/* We don't want the core code to modify any port params */
+	return -EINVAL;
+}
+
+
+static const char *serial_m3110_type(struct uart_port *port)
+{
+	struct uart_max3110 *max =
+		container_of(port, struct uart_max3110, port);
+	return max->name;
+}
+
+static void
+serial_m3110_set_termios(struct uart_port *port, struct ktermios *termios,
+		       struct ktermios *old)
+{
+	struct uart_max3110 *max =
+		container_of(port, struct uart_max3110, port);
+	unsigned char cval;
+	unsigned int baud, parity = 0;
+	int clk_div = -1;
+	u16 new_conf = max->cur_conf;
+
+	switch (termios->c_cflag & CSIZE) {
+	case CS7:
+		cval = UART_LCR_WLEN7;
+		new_conf |= WC_7BIT_WORD;
+		break;
+	default:
+		/* We only support CS7 & CS8 */
+		termios->c_cflag &= ~CSIZE;
+		termios->c_cflag |= CS8;
+	case CS8:
+		cval = UART_LCR_WLEN8;
+		new_conf |= WC_8BIT_WORD;
+		break;
+	}
+
+	baud = uart_get_baud_rate(port, termios, old, 0, 230400);
+
+	/* First calc the div for 1.8MHZ clock case */
+	switch (baud) {
+	case 300:
+		clk_div = WC_BAUD_DR384;
+		break;
+	case 600:
+		clk_div = WC_BAUD_DR192;
+		break;
+	case 1200:
+		clk_div = WC_BAUD_DR96;
+		break;
+	case 2400:
+		clk_div = WC_BAUD_DR48;
+		break;
+	case 4800:
+		clk_div = WC_BAUD_DR24;
+		break;
+	case 9600:
+		clk_div = WC_BAUD_DR12;
+		break;
+	case 19200:
+		clk_div = WC_BAUD_DR6;
+		break;
+	case 38400:
+		clk_div = WC_BAUD_DR3;
+		break;
+	case 57600:
+		clk_div = WC_BAUD_DR2;
+		break;
+	case 115200:
+		clk_div = WC_BAUD_DR1;
+		break;
+	case 230400:
+		if (max->clock & MAX3110_HIGH_CLK)
+			break;
+	default:
+		/* Pick the previous baud rate */
+		baud = max->baud;
+		clk_div = max->cur_conf & WC_BAUD_DIV_MASK;
+		tty_termios_encode_baud_rate(termios, baud, baud);
+	}
+
+	if (max->clock & MAX3110_HIGH_CLK) {
+		clk_div += 1;
+		/* High clk version max3110 doesn't support B300 */
+		if (baud == 300)
+			baud = 600;
+		if (baud == 230400)
+			clk_div = WC_BAUD_DR1;
+		tty_termios_encode_baud_rate(termios, baud, baud);
+	}
+
+	new_conf = (new_conf & ~WC_BAUD_DIV_MASK) | clk_div;
+
+	if (unlikely(termios->c_cflag & CMSPAR))
+		termios->c_cflag &= ~CMSPAR;
+
+	if (termios->c_cflag & CSTOPB)
+		new_conf |= WC_2_STOPBITS;
+	else
+		new_conf &= ~WC_2_STOPBITS;
+
+	if (termios->c_cflag & PARENB) {
+		new_conf |= WC_PARITY_ENABLE;
+		parity |= UART_LCR_PARITY;
+	} else
+		new_conf &= ~WC_PARITY_ENABLE;
+
+	if (!(termios->c_cflag & PARODD))
+		parity |= UART_LCR_EPAR;
+	max->parity = parity;
+
+	uart_update_timeout(port, termios->c_cflag, baud);
+
+	new_conf |= WC_TAG;
+	if (new_conf != max->cur_conf) {
+		if (!max3110_out(max, new_conf)) {
+			max->cur_conf = new_conf;
+			max->baud = baud;
+		}
+	}
+}
+
+/* Don't handle hw handshaking */
+static unsigned int serial_m3110_get_mctrl(struct uart_port *port)
+{
+	return TIOCM_DSR | TIOCM_CAR | TIOCM_DSR;
+}
+
+static void serial_m3110_set_mctrl(struct uart_port *port, unsigned int mctrl)
+{
+}
+
+static void serial_m3110_break_ctl(struct uart_port *port, int break_state)
+{
+}
+
+static void serial_m3110_pm(struct uart_port *port, unsigned int state,
+			unsigned int oldstate)
+{
+}
+
+static void serial_m3110_enable_ms(struct uart_port *port)
+{
+}
+
+struct uart_ops serial_m3110_ops = {
+	.tx_empty	= serial_m3110_tx_empty,
+	.set_mctrl	= serial_m3110_set_mctrl,
+	.get_mctrl	= serial_m3110_get_mctrl,
+	.stop_tx	= serial_m3110_stop_tx,
+	.start_tx	= serial_m3110_start_tx,
+	.stop_rx	= serial_m3110_stop_rx,
+	.enable_ms	= serial_m3110_enable_ms,
+	.break_ctl	= serial_m3110_break_ctl,
+	.startup	= serial_m3110_startup,
+	.shutdown	= serial_m3110_shutdown,
+	.set_termios	= serial_m3110_set_termios,
+	.pm		= serial_m3110_pm,
+	.type		= serial_m3110_type,
+	.release_port	= serial_m3110_release_port,
+	.request_port	= serial_m3110_request_port,
+	.config_port	= serial_m3110_config_port,
+	.verify_port	= serial_m3110_verify_port,
+};
+
+static struct uart_driver serial_m3110_reg = {
+	.owner		= THIS_MODULE,
+	.driver_name	= "Maxim 3110",
+	.dev_name	= "ttyS",
+	.major		= TTY_MAJOR,
+	.minor		= 64,
+	.nr		= 1,
+	.cons		= &serial_m3110_console,
+};
+
+#ifdef CONFIG_PM
+static int serial_m3110_suspend(struct spi_device *spi, pm_message_t state)
+{
+	disable_irq(pmax->irq);
+	uart_suspend_port(&serial_m3110_reg, &pmax->port);
+	max3110_out(pmax, pmax->cur_conf | WC_SW_SHDI);
+	return 0;
+}
+
+static int serial_m3110_resume(struct spi_device *spi)
+{
+	max3110_out(pmax, pmax->cur_conf);
+	uart_resume_port(&serial_m3110_reg, &pmax->port);
+	enable_irq(pmax->irq);
+	return 0;
+}
+#else
+#define serial_m3110_suspend	NULL
+#define serial_m3110_resume	NULL
+#endif
+
+static int __devinit serial_m3110_probe(struct spi_device *spi)
+{
+	struct uart_max3110 *max;
+	int ret;
+	void *buffer;
+
+	max = kzalloc(sizeof(*max), GFP_KERNEL);
+	if (!max)
+		return -ENOMEM;
+
+	spi->bits_per_word = 16;
+	spi_setup(spi);
+
+	max->clock = MAX3110_HIGH_CLK;
+	max->port.type = PORT_MAX3110;
+	max->port.fifosize = 2;		/* Only have 16b buffer */
+	max->port.ops = &serial_m3110_ops;
+	max->port.line = 0;
+	max->port.dev = &spi->dev;
+	max->port.uartclk = 115200;
+
+	max->spi = spi;
+	max->name = spi->modalias;	/* Use spi name as the name */
+	max->irq = (u16)spi->irq;
+	spin_lock_init(&max->lock);
+
+	max->word_7bits = 0;
+	max->parity = 0;
+	max->baud = 0;
+
+	max->cur_conf = 0;
+	max->flags = 0;
+
+	buffer = (void *)__get_free_page(GFP_KERNEL);
+	if (!buffer) {
+		ret = -ENOMEM;
+		goto err_get_page;
+	}
+	max->con_xmit.buf = buffer;
+	max->con_xmit.head = max->con_xmit.tail = 0;
+
+	max->main_thread = kthread_run(max3110_main_thread,
+					max, "max3110_main");
+	if (IS_ERR(max->main_thread)) {
+		ret = PTR_ERR(max->main_thread);
+		goto err_kthread;
+	}
+
+	pmax = max;
+	/* Give membase a psudo value to pass serial_core's check */
+	max->port.membase = buffer;
+	uart_add_one_port(&serial_m3110_reg, &max->port);
+
+	return 0;
+
+err_kthread:
+	free_page((unsigned long)buffer);
+err_get_page:
+	pmax = NULL;
+	kfree(max);
+	return ret;
+}
+
+static int __devexit max3110_remove(struct spi_device *dev)
+{
+	struct uart_max3110 *max = pmax;
+
+	if (!pmax)
+		return 0;
+
+	pmax = NULL;
+	uart_remove_one_port(&serial_m3110_reg, &max->port);
+
+	free_page((unsigned long)max->con_xmit.buf);
+
+	if (max->main_thread)
+		kthread_stop(max->main_thread);
+
+	kfree(max);
+	return 0;
+}
+
+static struct spi_driver uart_max3110_driver = {
+	.driver = {
+			.name	= "spi_max3110",
+			.bus	= &spi_bus_type,
+			.owner	= THIS_MODULE,
+	},
+	.probe		= serial_m3110_probe,
+	.remove		= __devexit_p(max3110_remove),
+	.suspend	= serial_m3110_suspend,
+	.resume		= serial_m3110_resume,
+};
+
+static int __init serial_m3110_init(void)
+{
+	int ret = 0;
+
+	ret = uart_register_driver(&serial_m3110_reg);
+	if (ret)
+		return ret;
+
+	ret = spi_register_driver(&uart_max3110_driver);
+	if (ret)
+		uart_unregister_driver(&serial_m3110_reg);
+
+	return ret;
+}
+
+static void __exit serial_m3110_exit(void)
+{
+	spi_unregister_driver(&uart_max3110_driver);
+	uart_unregister_driver(&serial_m3110_reg);
+}
+
+module_init(serial_m3110_init);
+module_exit(serial_m3110_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("max3110-uart");
+MODULE_AUTHOR("Feng Tang <feng.tang@intel.com>");
diff --git a/drivers/serial/max3110.h b/drivers/serial/max3110.h
new file mode 100644
index 0000000..4d58641
--- /dev/null
+++ b/drivers/serial/max3110.h
@@ -0,0 +1,61 @@
+#ifndef _MAX3110_HEAD_FILE_
+#define _MAX3110_HEAD_FILE_
+
+#define MAX3110_HIGH_CLK	0x1	/* 3.6864 MHZ */
+#define MAX3110_LOW_CLK		0x0	/* 1.8432 MHZ */
+
+/* Status bits for all 4 MAX3110 operate modes */
+#define MAX3110_READ_DATA_AVAILABLE	(1 << 15)
+#define MAX3110_WRITE_BUF_EMPTY		(1 << 14)
+
+#define WC_TAG			(3 << 14)
+#define RC_TAG			(1 << 14)
+#define WD_TAG			(2 << 14)
+#define RD_TAG			(0 << 14)
+
+/* Bits def for write configuration */
+#define WC_FIFO_ENABLE_MASK	(1 << 13)
+#define WC_FIFO_ENABLE		(0 << 13)
+
+#define WC_SW_SHDI		(1 << 12)
+
+#define WC_IRQ_MASK		(0xF << 8)
+#define WC_TXE_IRQ_ENABLE	(1 << 11)	/* TX empty irq */
+#define WC_RXA_IRQ_ENABLE	(1 << 10)	/* RX availabe irq */
+#define WC_PAR_HIGH_IRQ_ENABLE	(1 << 9)
+#define WC_REC_ACT_IRQ_ENABLE	(1 << 8)
+
+#define WC_IRDA_ENABLE		(1 << 7)
+
+#define WC_STOPBITS_MASK	(1 << 6)
+#define WC_2_STOPBITS		(1 << 6)
+#define WC_1_STOPBITS		(0 << 6)
+
+#define WC_PARITY_ENABLE_MASK	(1 << 5)
+#define WC_PARITY_ENABLE	(1 << 5)
+
+#define WC_WORDLEN_MASK		(1 << 4)
+#define WC_7BIT_WORD		(1 << 4)
+#define WC_8BIT_WORD		(0 << 4)
+
+#define WC_BAUD_DIV_MASK	(0xF)
+#define WC_BAUD_DR1		(0x0)
+#define WC_BAUD_DR2		(0x1)
+#define WC_BAUD_DR4		(0x2)
+#define WC_BAUD_DR8		(0x3)
+#define WC_BAUD_DR16		(0x4)
+#define WC_BAUD_DR32		(0x5)
+#define WC_BAUD_DR64		(0x6)
+#define WC_BAUD_DR128		(0x7)
+#define WC_BAUD_DR3		(0x8)
+#define WC_BAUD_DR6		(0x9)
+#define WC_BAUD_DR12		(0xA)
+#define WC_BAUD_DR24		(0xB)
+#define WC_BAUD_DR48		(0xC)
+#define WC_BAUD_DR96		(0xD)
+#define WC_BAUD_DR192		(0xE)
+#define WC_BAUD_DR384		(0xF)
+
+/* Maxim 3110 has 8 words RX FIFO and 1 word TX FIFO */
+#define M3110_RX_FIFO_DEPTH	8
+#endif
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 8c3dd36..119ba73 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -182,6 +182,9 @@
 /* Aeroflex Gaisler GRLIB APBUART */
 #define PORT_APBUART    90
 
+/* Maxim M3110 */
+#define PORT_MAX3110	91
+
 #ifdef __KERNEL__
 
 #include <linux/compiler.h>
-- 
1.6.3.3