xref: /openbmc/linux/drivers/tty/serial/max3100.c (revision a0386bba70934d42f586eaf68b21d5eeaffa7bd0)

// SPDX-License-Identifier: GPL-2.0+
/*
 *
 *  Copyright (C) 2008 Christian Pellegrin <chripell@evolware.org>
 *
 * Notes: the MAX3100 doesn't provide an interrupt on CTS so we have
 * to use polling for flow control. TX empty IRQ is unusable, since
 * writing conf clears FIFO buffer and we cannot have this interrupt
 * always asking us for attention.
 *
 * Example platform data:

 static struct plat_max3100 max3100_plat_data = {
 .loopback = 0,
 .crystal = 0,
 .poll_time = 100,
 };

 static struct spi_board_info spi_board_info[] = {
 {
 .modalias	= "max3100",
 .platform_data	= &max3100_plat_data,
 .irq		= IRQ_EINT12,
 .max_speed_hz	= 5*1000*1000,
 .chip_select	= 0,
 },
 };

 * The initial minor number is 209 in the low-density serial port:
 * mknod /dev/ttyMAX0 c 204 209
 */

#define MAX3100_MAJOR 204
#define MAX3100_MINOR 209
/* 4 MAX3100s should be enough for everyone */
#define MAX_MAX3100 4

#include <linux/delay.h>
#include <linux/slab.h>
#include <linux/device.h>
#include <linux/module.h>
#include <linux/serial_core.h>
#include <linux/serial.h>
#include <linux/spi/spi.h>
#include <linux/freezer.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>

#include <linux/serial_max3100.h>

#define MAX3100_C    (1<<14)
#define MAX3100_D    (0<<14)
#define MAX3100_W    (1<<15)
#define MAX3100_RX   (0<<15)

#define MAX3100_WC   (MAX3100_W  | MAX3100_C)
#define MAX3100_RC   (MAX3100_RX | MAX3100_C)
#define MAX3100_WD   (MAX3100_W  | MAX3100_D)
#define MAX3100_RD   (MAX3100_RX | MAX3100_D)
#define MAX3100_CMD  (3 << 14)

#define MAX3100_T    (1<<14)
#define MAX3100_R    (1<<15)

#define MAX3100_FEN  (1<<13)
#define MAX3100_SHDN (1<<12)
#define MAX3100_TM   (1<<11)
#define MAX3100_RM   (1<<10)
#define MAX3100_PM   (1<<9)
#define MAX3100_RAM  (1<<8)
#define MAX3100_IR   (1<<7)
#define MAX3100_ST   (1<<6)
#define MAX3100_PE   (1<<5)
#define MAX3100_L    (1<<4)
#define MAX3100_BAUD (0xf)

#define MAX3100_TE   (1<<10)
#define MAX3100_RAFE (1<<10)
#define MAX3100_RTS  (1<<9)
#define MAX3100_CTS  (1<<9)
#define MAX3100_PT   (1<<8)
#define MAX3100_DATA (0xff)

#define MAX3100_RT   (MAX3100_R | MAX3100_T)
#define MAX3100_RTC  (MAX3100_RT | MAX3100_CTS | MAX3100_RAFE)

/* the following simulate a status reg for ignore_status_mask */
#define MAX3100_STATUS_PE 1
#define MAX3100_STATUS_FE 2
#define MAX3100_STATUS_OE 4

struct max3100_port {
	struct uart_port port;
	struct spi_device *spi;

	int cts;	        /* last CTS received for flow ctrl */
	int tx_empty;		/* last TX empty bit */

	spinlock_t conf_lock;	/* shared data */
	int conf_commit;	/* need to make changes */
	int conf;		/* configuration for the MAX31000
				 * (bits 0-7, bits 8-11 are irqs) */
	int rts_commit;	        /* need to change rts */
	int rts;		/* rts status */
	int baud;		/* current baud rate */

	int parity;		/* keeps track if we should send parity */
#define MAX3100_PARITY_ON 1
#define MAX3100_PARITY_ODD 2
#define MAX3100_7BIT 4
	int rx_enabled;	        /* if we should rx chars */

	int irq;		/* irq assigned to the max3100 */

	int minor;		/* minor number */
	int crystal;		/* 1 if 3.6864Mhz crystal 0 for 1.8432 */
	int loopback;		/* 1 if we are in loopback mode */

	/* for handling irqs: need workqueue since we do spi_sync */
	struct workqueue_struct *workqueue;
	struct work_struct work;
	/* set to 1 to make the workhandler exit as soon as possible */
	int  force_end_work;
	/* need to know we are suspending to avoid deadlock on workqueue */
	int suspending;

	/* hook for suspending MAX3100 via dedicated pin */
	void (*max3100_hw_suspend) (int suspend);

	/* poll time (in ms) for ctrl lines */
	int poll_time;
	/* and its timer */
	struct timer_list	timer;
};

static struct max3100_port *max3100s[MAX_MAX3100]; /* the chips */
static DEFINE_MUTEX(max3100s_lock);		   /* race on probe */

static int max3100_do_parity(struct max3100_port *s, u16 c)
{
	int parity;

	if (s->parity & MAX3100_PARITY_ODD)
		parity = 1;
	else
		parity = 0;

	if (s->parity & MAX3100_7BIT)
		c &= 0x7f;
	else
		c &= 0xff;

	parity = parity ^ (hweight8(c) & 1);
	return parity;
}

static int max3100_check_parity(struct max3100_port *s, u16 c)
{
	return max3100_do_parity(s, c) == ((c >> 8) & 1);
}

static void max3100_calc_parity(struct max3100_port *s, u16 *c)
{
	if (s->parity & MAX3100_7BIT)
		*c &= 0x7f;
	else
		*c &= 0xff;

	if (s->parity & MAX3100_PARITY_ON)
		*c |= max3100_do_parity(s, *c) << 8;
}

static void max3100_work(struct work_struct *w);

static void max3100_dowork(struct max3100_port *s)
{
	if (!s->force_end_work && !freezing(current) && !s->suspending)
		queue_work(s->workqueue, &s->work);
}

static void max3100_timeout(struct timer_list *t)
{
	struct max3100_port *s = from_timer(s, t, timer);

	if (s->port.state) {
		max3100_dowork(s);
		mod_timer(&s->timer, jiffies + s->poll_time);
	}
}

static int max3100_sr(struct max3100_port *s, u16 tx, u16 *rx)
{
	struct spi_message message;
	u16 etx, erx;
	int status;
	struct spi_transfer tran = {
		.tx_buf = &etx,
		.rx_buf = &erx,
		.len = 2,
	};

	etx = cpu_to_be16(tx);
	spi_message_init(&message);
	spi_message_add_tail(&tran, &message);
	status = spi_sync(s->spi, &message);
	if (status) {
		dev_warn(&s->spi->dev, "error while calling spi_sync\n");
		return -EIO;
	}
	*rx = be16_to_cpu(erx);
	s->tx_empty = (*rx & MAX3100_T) > 0;
	dev_dbg(&s->spi->dev, "%04x - %04x\n", tx, *rx);
	return 0;
}

static int max3100_handlerx(struct max3100_port *s, u16 rx)
{
	unsigned int ch, flg, status = 0;
	int ret = 0, cts;

	if (rx & MAX3100_R && s->rx_enabled) {
		dev_dbg(&s->spi->dev, "%s\n", __func__);
		ch = rx & (s->parity & MAX3100_7BIT ? 0x7f : 0xff);
		if (rx & MAX3100_RAFE) {
			s->port.icount.frame++;
			flg = TTY_FRAME;
			status |= MAX3100_STATUS_FE;
		} else {
			if (s->parity & MAX3100_PARITY_ON) {
				if (max3100_check_parity(s, rx)) {
					s->port.icount.rx++;
					flg = TTY_NORMAL;
				} else {
					s->port.icount.parity++;
					flg = TTY_PARITY;
					status |= MAX3100_STATUS_PE;
				}
			} else {
				s->port.icount.rx++;
				flg = TTY_NORMAL;
			}
		}
		uart_insert_char(&s->port, status, MAX3100_STATUS_OE, ch, flg);
		ret = 1;
	}

	cts = (rx & MAX3100_CTS) > 0;
	if (s->cts != cts) {
		s->cts = cts;
		uart_handle_cts_change(&s->port, cts ? TIOCM_CTS : 0);
	}

	return ret;
}

static void max3100_work(struct work_struct *w)
{
	struct max3100_port *s = container_of(w, struct max3100_port, work);
	int rxchars;
	u16 tx, rx;
	int conf, cconf, crts;
	struct circ_buf *xmit = &s->port.state->xmit;

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	rxchars = 0;
	do {
		spin_lock(&s->conf_lock);
		conf = s->conf;
		cconf = s->conf_commit;
		s->conf_commit = 0;
		crts = s->rts_commit;
		s->rts_commit = 0;
		spin_unlock(&s->conf_lock);
		if (cconf)
			max3100_sr(s, MAX3100_WC | conf, &rx);
		if (crts) {
			max3100_sr(s, MAX3100_WD | MAX3100_TE |
				   (s->rts ? MAX3100_RTS : 0), &rx);
			rxchars += max3100_handlerx(s, rx);
		}

		max3100_sr(s, MAX3100_RD, &rx);
		rxchars += max3100_handlerx(s, rx);

		if (rx & MAX3100_T) {
			tx = 0xffff;
			if (s->port.x_char) {
				tx = s->port.x_char;
				s->port.icount.tx++;
				s->port.x_char = 0;
			} else if (!uart_circ_empty(xmit) &&
				   !uart_tx_stopped(&s->port)) {
				tx = xmit->buf[xmit->tail];
				xmit->tail = (xmit->tail + 1) &
					(UART_XMIT_SIZE - 1);
				s->port.icount.tx++;
			}
			if (tx != 0xffff) {
				max3100_calc_parity(s, &tx);
				tx |= MAX3100_WD | (s->rts ? MAX3100_RTS : 0);
				max3100_sr(s, tx, &rx);
				rxchars += max3100_handlerx(s, rx);
			}
		}

		if (rxchars > 16) {
			tty_flip_buffer_push(&s->port.state->port);
			rxchars = 0;
		}
		if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
			uart_write_wakeup(&s->port);

	} while (!s->force_end_work &&
		 !freezing(current) &&
		 ((rx & MAX3100_R) ||
		  (!uart_circ_empty(xmit) &&
		   !uart_tx_stopped(&s->port))));

	if (rxchars > 0)
		tty_flip_buffer_push(&s->port.state->port);
}

static irqreturn_t max3100_irq(int irqno, void *dev_id)
{
	struct max3100_port *s = dev_id;

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	max3100_dowork(s);
	return IRQ_HANDLED;
}

static void max3100_enable_ms(struct uart_port *port)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);

	if (s->poll_time > 0)
		mod_timer(&s->timer, jiffies);
	dev_dbg(&s->spi->dev, "%s\n", __func__);
}

static void max3100_start_tx(struct uart_port *port)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	max3100_dowork(s);
}

static void max3100_stop_rx(struct uart_port *port)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	s->rx_enabled = 0;
	spin_lock(&s->conf_lock);
	s->conf &= ~MAX3100_RM;
	s->conf_commit = 1;
	spin_unlock(&s->conf_lock);
	max3100_dowork(s);
}

static unsigned int max3100_tx_empty(struct uart_port *port)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	/* may not be truly up-to-date */
	max3100_dowork(s);
	return s->tx_empty;
}

static unsigned int max3100_get_mctrl(struct uart_port *port)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	/* may not be truly up-to-date */
	max3100_dowork(s);
	/* always assert DCD and DSR since these lines are not wired */
	return (s->cts ? TIOCM_CTS : 0) | TIOCM_DSR | TIOCM_CAR;
}

static void max3100_set_mctrl(struct uart_port *port, unsigned int mctrl)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);
	int rts;

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	rts = (mctrl & TIOCM_RTS) > 0;

	spin_lock(&s->conf_lock);
	if (s->rts != rts) {
		s->rts = rts;
		s->rts_commit = 1;
		max3100_dowork(s);
	}
	spin_unlock(&s->conf_lock);
}

static void
max3100_set_termios(struct uart_port *port, struct ktermios *termios,
		    struct ktermios *old)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);
	int baud = 0;
	unsigned cflag;
	u32 param_new, param_mask, parity = 0;

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	cflag = termios->c_cflag;
	param_mask = 0;

	baud = tty_termios_baud_rate(termios);
	param_new = s->conf & MAX3100_BAUD;
	switch (baud) {
	case 300:
		if (s->crystal)
			baud = s->baud;
		else
			param_new = 15;
		break;
	case 600:
		param_new = 14 + s->crystal;
		break;
	case 1200:
		param_new = 13 + s->crystal;
		break;
	case 2400:
		param_new = 12 + s->crystal;
		break;
	case 4800:
		param_new = 11 + s->crystal;
		break;
	case 9600:
		param_new = 10 + s->crystal;
		break;
	case 19200:
		param_new = 9 + s->crystal;
		break;
	case 38400:
		param_new = 8 + s->crystal;
		break;
	case 57600:
		param_new = 1 + s->crystal;
		break;
	case 115200:
		param_new = 0 + s->crystal;
		break;
	case 230400:
		if (s->crystal)
			param_new = 0;
		else
			baud = s->baud;
		break;
	default:
		baud = s->baud;
	}
	tty_termios_encode_baud_rate(termios, baud, baud);
	s->baud = baud;
	param_mask |= MAX3100_BAUD;

	if ((cflag & CSIZE) == CS8) {
		param_new &= ~MAX3100_L;
		parity &= ~MAX3100_7BIT;
	} else {
		param_new |= MAX3100_L;
		parity |= MAX3100_7BIT;
		cflag = (cflag & ~CSIZE) | CS7;
	}
	param_mask |= MAX3100_L;

	if (cflag & CSTOPB)
		param_new |= MAX3100_ST;
	else
		param_new &= ~MAX3100_ST;
	param_mask |= MAX3100_ST;

	if (cflag & PARENB) {
		param_new |= MAX3100_PE;
		parity |= MAX3100_PARITY_ON;
	} else {
		param_new &= ~MAX3100_PE;
		parity &= ~MAX3100_PARITY_ON;
	}
	param_mask |= MAX3100_PE;

	if (cflag & PARODD)
		parity |= MAX3100_PARITY_ODD;
	else
		parity &= ~MAX3100_PARITY_ODD;

	/* mask termios capabilities we don't support */
	cflag &= ~CMSPAR;
	termios->c_cflag = cflag;

	s->port.ignore_status_mask = 0;
	if (termios->c_iflag & IGNPAR)
		s->port.ignore_status_mask |=
			MAX3100_STATUS_PE | MAX3100_STATUS_FE |
			MAX3100_STATUS_OE;

	if (s->poll_time > 0)
		del_timer_sync(&s->timer);

	uart_update_timeout(port, termios->c_cflag, baud);

	spin_lock(&s->conf_lock);
	s->conf = (s->conf & ~param_mask) | (param_new & param_mask);
	s->conf_commit = 1;
	s->parity = parity;
	spin_unlock(&s->conf_lock);
	max3100_dowork(s);

	if (UART_ENABLE_MS(&s->port, termios->c_cflag))
		max3100_enable_ms(&s->port);
}

static void max3100_shutdown(struct uart_port *port)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	if (s->suspending)
		return;

	s->force_end_work = 1;

	if (s->poll_time > 0)
		del_timer_sync(&s->timer);

	if (s->workqueue) {
		flush_workqueue(s->workqueue);
		destroy_workqueue(s->workqueue);
		s->workqueue = NULL;
	}
	if (s->irq)
		free_irq(s->irq, s);

	/* set shutdown mode to save power */
	if (s->max3100_hw_suspend)
		s->max3100_hw_suspend(1);
	else  {
		u16 tx, rx;

		tx = MAX3100_WC | MAX3100_SHDN;
		max3100_sr(s, tx, &rx);
	}
}

static int max3100_startup(struct uart_port *port)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);
	char b[12];

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	s->conf = MAX3100_RM;
	s->baud = s->crystal ? 230400 : 115200;
	s->rx_enabled = 1;

	if (s->suspending)
		return 0;

	s->force_end_work = 0;
	s->parity = 0;
	s->rts = 0;

	sprintf(b, "max3100-%d", s->minor);
	s->workqueue = create_freezable_workqueue(b);
	if (!s->workqueue) {
		dev_warn(&s->spi->dev, "cannot create workqueue\n");
		return -EBUSY;
	}
	INIT_WORK(&s->work, max3100_work);

	if (request_irq(s->irq, max3100_irq,
			IRQF_TRIGGER_FALLING, "max3100", s) < 0) {
		dev_warn(&s->spi->dev, "cannot allocate irq %d\n", s->irq);
		s->irq = 0;
		destroy_workqueue(s->workqueue);
		s->workqueue = NULL;
		return -EBUSY;
	}

	if (s->loopback) {
		u16 tx, rx;
		tx = 0x4001;
		max3100_sr(s, tx, &rx);
	}

	if (s->max3100_hw_suspend)
		s->max3100_hw_suspend(0);
	s->conf_commit = 1;
	max3100_dowork(s);
	/* wait for clock to settle */
	msleep(50);

	max3100_enable_ms(&s->port);

	return 0;
}

static const char *max3100_type(struct uart_port *port)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	return s->port.type == PORT_MAX3100 ? "MAX3100" : NULL;
}

static void max3100_release_port(struct uart_port *port)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);

	dev_dbg(&s->spi->dev, "%s\n", __func__);
}

static void max3100_config_port(struct uart_port *port, int flags)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	if (flags & UART_CONFIG_TYPE)
		s->port.type = PORT_MAX3100;
}

static int max3100_verify_port(struct uart_port *port,
			       struct serial_struct *ser)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);
	int ret = -EINVAL;

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	if (ser->type == PORT_UNKNOWN || ser->type == PORT_MAX3100)
		ret = 0;
	return ret;
}

static void max3100_stop_tx(struct uart_port *port)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);

	dev_dbg(&s->spi->dev, "%s\n", __func__);
}

static int max3100_request_port(struct uart_port *port)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);

	dev_dbg(&s->spi->dev, "%s\n", __func__);
	return 0;
}

static void max3100_break_ctl(struct uart_port *port, int break_state)
{
	struct max3100_port *s = container_of(port,
					      struct max3100_port,
					      port);

	dev_dbg(&s->spi->dev, "%s\n", __func__);
}

static const struct uart_ops max3100_ops = {
	.tx_empty	= max3100_tx_empty,
	.set_mctrl	= max3100_set_mctrl,
	.get_mctrl	= max3100_get_mctrl,
	.stop_tx        = max3100_stop_tx,
	.start_tx	= max3100_start_tx,
	.stop_rx	= max3100_stop_rx,
	.enable_ms      = max3100_enable_ms,
	.break_ctl      = max3100_break_ctl,
	.startup	= max3100_startup,
	.shutdown	= max3100_shutdown,
	.set_termios	= max3100_set_termios,
	.type		= max3100_type,
	.release_port   = max3100_release_port,
	.request_port   = max3100_request_port,
	.config_port	= max3100_config_port,
	.verify_port	= max3100_verify_port,
};

static struct uart_driver max3100_uart_driver = {
	.owner          = THIS_MODULE,
	.driver_name    = "ttyMAX",
	.dev_name       = "ttyMAX",
	.major          = MAX3100_MAJOR,
	.minor          = MAX3100_MINOR,
	.nr             = MAX_MAX3100,
};
static int uart_driver_registered;

static int max3100_probe(struct spi_device *spi)
{
	int i, retval;
	struct plat_max3100 *pdata;
	u16 tx, rx;

	mutex_lock(&max3100s_lock);

	if (!uart_driver_registered) {
		uart_driver_registered = 1;
		retval = uart_register_driver(&max3100_uart_driver);
		if (retval) {
			printk(KERN_ERR "Couldn't register max3100 uart driver\n");
			mutex_unlock(&max3100s_lock);
			return retval;
		}
	}

	for (i = 0; i < MAX_MAX3100; i++)
		if (!max3100s[i])
			break;
	if (i == MAX_MAX3100) {
		dev_warn(&spi->dev, "too many MAX3100 chips\n");
		mutex_unlock(&max3100s_lock);
		return -ENOMEM;
	}

	max3100s[i] = kzalloc(sizeof(struct max3100_port), GFP_KERNEL);
	if (!max3100s[i]) {
		dev_warn(&spi->dev,
			 "kmalloc for max3100 structure %d failed!\n", i);
		mutex_unlock(&max3100s_lock);
		return -ENOMEM;
	}
	max3100s[i]->spi = spi;
	max3100s[i]->irq = spi->irq;
	spin_lock_init(&max3100s[i]->conf_lock);
	spi_set_drvdata(spi, max3100s[i]);
	pdata = dev_get_platdata(&spi->dev);
	max3100s[i]->crystal = pdata->crystal;
	max3100s[i]->loopback = pdata->loopback;
	max3100s[i]->poll_time = msecs_to_jiffies(pdata->poll_time);
	if (pdata->poll_time > 0 && max3100s[i]->poll_time == 0)
		max3100s[i]->poll_time = 1;
	max3100s[i]->max3100_hw_suspend = pdata->max3100_hw_suspend;
	max3100s[i]->minor = i;
	timer_setup(&max3100s[i]->timer, max3100_timeout, 0);

	dev_dbg(&spi->dev, "%s: adding port %d\n", __func__, i);
	max3100s[i]->port.irq = max3100s[i]->irq;
	max3100s[i]->port.uartclk = max3100s[i]->crystal ? 3686400 : 1843200;
	max3100s[i]->port.fifosize = 16;
	max3100s[i]->port.ops = &max3100_ops;
	max3100s[i]->port.flags = UPF_SKIP_TEST | UPF_BOOT_AUTOCONF;
	max3100s[i]->port.line = i;
	max3100s[i]->port.type = PORT_MAX3100;
	max3100s[i]->port.dev = &spi->dev;
	retval = uart_add_one_port(&max3100_uart_driver, &max3100s[i]->port);
	if (retval < 0)
		dev_warn(&spi->dev,
			 "uart_add_one_port failed for line %d with error %d\n",
			 i, retval);

	/* set shutdown mode to save power. Will be woken-up on open */
	if (max3100s[i]->max3100_hw_suspend)
		max3100s[i]->max3100_hw_suspend(1);
	else {
		tx = MAX3100_WC | MAX3100_SHDN;
		max3100_sr(max3100s[i], tx, &rx);
	}
	mutex_unlock(&max3100s_lock);
	return 0;
}

static void max3100_remove(struct spi_device *spi)
{
	struct max3100_port *s = spi_get_drvdata(spi);
	int i;

	mutex_lock(&max3100s_lock);

	/* find out the index for the chip we are removing */
	for (i = 0; i < MAX_MAX3100; i++)
		if (max3100s[i] == s) {
			dev_dbg(&spi->dev, "%s: removing port %d\n", __func__, i);
			uart_remove_one_port(&max3100_uart_driver, &max3100s[i]->port);
			kfree(max3100s[i]);
			max3100s[i] = NULL;
			break;
		}

	WARN_ON(i == MAX_MAX3100);

	/* check if this is the last chip we have */
	for (i = 0; i < MAX_MAX3100; i++)
		if (max3100s[i]) {
			mutex_unlock(&max3100s_lock);
			return;
		}
	pr_debug("removing max3100 driver\n");
	uart_unregister_driver(&max3100_uart_driver);

	mutex_unlock(&max3100s_lock);
}

#ifdef CONFIG_PM_SLEEP

static int max3100_suspend(struct device *dev)
{
	struct max3100_port *s = dev_get_drvdata(dev);

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	disable_irq(s->irq);

	s->suspending = 1;
	uart_suspend_port(&max3100_uart_driver, &s->port);

	if (s->max3100_hw_suspend)
		s->max3100_hw_suspend(1);
	else {
		/* no HW suspend, so do SW one */
		u16 tx, rx;

		tx = MAX3100_WC | MAX3100_SHDN;
		max3100_sr(s, tx, &rx);
	}
	return 0;
}

static int max3100_resume(struct device *dev)
{
	struct max3100_port *s = dev_get_drvdata(dev);

	dev_dbg(&s->spi->dev, "%s\n", __func__);

	if (s->max3100_hw_suspend)
		s->max3100_hw_suspend(0);
	uart_resume_port(&max3100_uart_driver, &s->port);
	s->suspending = 0;

	enable_irq(s->irq);

	s->conf_commit = 1;
	if (s->workqueue)
		max3100_dowork(s);

	return 0;
}

static SIMPLE_DEV_PM_OPS(max3100_pm_ops, max3100_suspend, max3100_resume);
#define MAX3100_PM_OPS (&max3100_pm_ops)

#else
#define MAX3100_PM_OPS NULL
#endif

static struct spi_driver max3100_driver = {
	.driver = {
		.name		= "max3100",
		.pm		= MAX3100_PM_OPS,
	},
	.probe		= max3100_probe,
	.remove		= max3100_remove,
};

module_spi_driver(max3100_driver);

MODULE_DESCRIPTION("MAX3100 driver");
MODULE_AUTHOR("Christian Pellegrin <chripell@evolware.org>");
MODULE_LICENSE("GPL");
MODULE_ALIAS("spi:max3100");