serial_core.c

宋宝华的《Linux设备驱动开发详解》第一版的源代码

/*
 *  linux/drivers/char/core.c
 *
 *  Driver core for serial ports
 *
 *  Based on drivers/char/serial.c, by Linus Torvalds, Theodore Ts'o.
 *
 *  Copyright 1999 ARM Limited
 *  Copyright (C) 2000-2001 Deep Blue Solutions Ltd.
 *
 * 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
 */
#include <linux/config.h>
#include <linux/module.h>
#include <linux/tty.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/console.h>
#include <linux/serial_core.h>
#include <linux/smp_lock.h>
#include <linux/device.h>
#include <linux/serial.h> /* for serial_state and serial_icounter_struct */
#include <linux/delay.h>
#include <linux/mutex.h>

#include <asm/irq.h>
#include <asm/uaccess.h>

#undef	DEBUG
#ifdef DEBUG
#define DPRINTK(x...)	printk(x)
#else
#define DPRINTK(x...)	do { } while (0)
#endif

/*
 * This is used to lock changes in serial line configuration.
 */
static DEFINE_MUTEX(port_mutex);

#define HIGH_BITS_OFFSET	((sizeof(long)-sizeof(int))*8)

#define uart_users(state)	((state)->count + ((state)->info ? (state)->info->blocked_open : 0))

#ifdef CONFIG_SERIAL_CORE_CONSOLE
#define uart_console(port)	((port)->cons && (port)->cons->index == (port)->line)
#else
#define uart_console(port)	(0)
#endif

static void uart_change_speed(struct uart_state *state, struct termios *old_termios);
static void uart_wait_until_sent(struct tty_struct *tty, int timeout);
static void uart_change_pm(struct uart_state *state, int pm_state);

/*
 * This routine is used by the interrupt handler to schedule processing in
 * the software interrupt portion of the driver.
 */
void uart_write_wakeup(struct uart_port *port)
{
	struct uart_info *info = port->info;
	/*
	 * This means you called this function _after_ the port was
	 * closed.  No cookie for you.
	 */
	BUG_ON(!info);
	tasklet_schedule(&info->tlet);
}

static void uart_stop(struct tty_struct *tty)
{
	struct uart_state *state = tty->driver_data;
	struct uart_port *port = state->port;
	unsigned long flags;

	spin_lock_irqsave(&port->lock, flags);
	port->ops->stop_tx(port);
	spin_unlock_irqrestore(&port->lock, flags);
}

static void __uart_start(struct tty_struct *tty)
{
	struct uart_state *state = tty->driver_data;
	struct uart_port *port = state->port;

	if (!uart_circ_empty(&state->info->xmit) && state->info->xmit.buf &&
	    !tty->stopped && !tty->hw_stopped)
		port->ops->start_tx(port);
}

static void uart_start(struct tty_struct *tty)
{
	struct uart_state *state = tty->driver_data;
	struct uart_port *port = state->port;
	unsigned long flags;

	spin_lock_irqsave(&port->lock, flags);
	__uart_start(tty);
	spin_unlock_irqrestore(&port->lock, flags);
}

static void uart_tasklet_action(unsigned long data)
{
	struct uart_state *state = (struct uart_state *)data;
	tty_wakeup(state->info->tty);
}

static inline void
uart_update_mctrl(struct uart_port *port, unsigned int set, unsigned int clear)
{
	unsigned long flags;
	unsigned int old;

	spin_lock_irqsave(&port->lock, flags);
	old = port->mctrl;
	port->mctrl = (old & ~clear) | set;
	if (old != port->mctrl)
		port->ops->set_mctrl(port, port->mctrl);
	spin_unlock_irqrestore(&port->lock, flags);
}

#define uart_set_mctrl(port,set)	uart_update_mctrl(port,set,0)
#define uart_clear_mctrl(port,clear)	uart_update_mctrl(port,0,clear)

/*
 * Startup the port.  This will be called once per open.  All calls
 * will be serialised by the per-port semaphore.
 */
static int uart_startup(struct uart_state *state, int init_hw)
{
	struct uart_info *info = state->info;
	struct uart_port *port = state->port;
	unsigned long page;
	int retval = 0;

	if (info->flags & UIF_INITIALIZED)
		return 0;

	/*
	 * Set the TTY IO error marker - we will only clear this
	 * once we have successfully opened the port.  Also set
	 * up the tty->alt_speed kludge
	 */
	set_bit(TTY_IO_ERROR, &info->tty->flags);

	if (port->type == PORT_UNKNOWN)
		return 0;

	/*
	 * Initialise and allocate the transmit and temporary
	 * buffer.
	 */
	if (!info->xmit.buf) {
		page = get_zeroed_page(GFP_KERNEL);
		if (!page)
			return -ENOMEM;

		info->xmit.buf = (unsigned char *) page;
		uart_circ_clear(&info->xmit);
	}

	retval = port->ops->startup(port);
	if (retval == 0) {
		if (init_hw) {
			/*
			 * Initialise the hardware port settings.
			 */
			uart_change_speed(state, NULL);

			/*
			 * Setup the RTS and DTR signals once the
			 * port is open and ready to respond.
			 */
			if (info->tty->termios->c_cflag & CBAUD)
				uart_set_mctrl(port, TIOCM_RTS | TIOCM_DTR);
		}

		if (info->flags & UIF_CTS_FLOW) {
			spin_lock_irq(&port->lock);
			if (!(port->ops->get_mctrl(port) & TIOCM_CTS))
				info->tty->hw_stopped = 1;
			spin_unlock_irq(&port->lock);
		}

		info->flags |= UIF_INITIALIZED;

		clear_bit(TTY_IO_ERROR, &info->tty->flags);
	}

	if (retval && capable(CAP_SYS_ADMIN))
		retval = 0;

	return retval;
}

/*
 * This routine will shutdown a serial port; interrupts are disabled, and
 * DTR is dropped if the hangup on close termio flag is on.  Calls to
 * uart_shutdown are serialised by the per-port semaphore.
 */
static void uart_shutdown(struct uart_state *state)
{
	struct uart_info *info = state->info;
	struct uart_port *port = state->port;

	/*
	 * Set the TTY IO error marker
	 */
	if (info->tty)
		set_bit(TTY_IO_ERROR, &info->tty->flags);

	if (info->flags & UIF_INITIALIZED) {
		info->flags &= ~UIF_INITIALIZED;

		/*
		 * Turn off DTR and RTS early.
		 */
		if (!info->tty || (info->tty->termios->c_cflag & HUPCL))
			uart_clear_mctrl(port, TIOCM_DTR | TIOCM_RTS);

		/*
		 * clear delta_msr_wait queue to avoid mem leaks: we may free
		 * the irq here so the queue might never be woken up.  Note
		 * that we won't end up waiting on delta_msr_wait again since
		 * any outstanding file descriptors should be pointing at
		 * hung_up_tty_fops now.
		 */
		wake_up_interruptible(&info->delta_msr_wait);

		/*
		 * Free the IRQ and disable the port.
		 */
		port->ops->shutdown(port);

		/*
		 * Ensure that the IRQ handler isn't running on another CPU.
		 */
		synchronize_irq(port->irq);
	}

	/*
	 * kill off our tasklet
	 */
	tasklet_kill(&info->tlet);

	/*
	 * Free the transmit buffer page.
	 */
	if (info->xmit.buf) {
		free_page((unsigned long)info->xmit.buf);
		info->xmit.buf = NULL;
	}
}

/**
 *	uart_update_timeout - update per-port FIFO timeout.
 *	@port:  uart_port structure describing the port
 *	@cflag: termios cflag value
 *	@baud:  speed of the port
 *
 *	Set the port FIFO timeout value.  The @cflag value should
 *	reflect the actual hardware settings.
 */
void
uart_update_timeout(struct uart_port *port, unsigned int cflag,
		    unsigned int baud)
{
	unsigned int bits;

	/* byte size and parity */
	switch (cflag & CSIZE) {
	case CS5:
		bits = 7;
		break;
	case CS6:
		bits = 8;
		break;
	case CS7:
		bits = 9;
		break;
	default:
		bits = 10;
		break; // CS8
	}

	if (cflag & CSTOPB)
		bits++;
	if (cflag & PARENB)
		bits++;

	/*
	 * The total number of bits to be transmitted in the fifo.
	 */
	bits = bits * port->fifosize;

	/*
	 * Figure the timeout to send the above number of bits.
	 * Add .02 seconds of slop
	 */
	port->timeout = (HZ * bits) / baud + HZ/50;
}

EXPORT_SYMBOL(uart_update_timeout);

/**
 *	uart_get_baud_rate - return baud rate for a particular port
 *	@port: uart_port structure describing the port in question.
 *	@termios: desired termios settings.
 *	@old: old termios (or NULL)
 *	@min: minimum acceptable baud rate
 *	@max: maximum acceptable baud rate
 *
 *	Decode the termios structure into a numeric baud rate,
 *	taking account of the magic 38400 baud rate (with spd_*
 *	flags), and mapping the %B0 rate to 9600 baud.
 *
 *	If the new baud rate is invalid, try the old termios setting.
 *	If it's still invalid, we try 9600 baud.
 *
 *	Update the @termios structure to reflect the baud rate
 *	we're actually going to be using.
 */
unsigned int
uart_get_baud_rate(struct uart_port *port, struct termios *termios,
		   struct termios *old, unsigned int min, unsigned int max)
{
	unsigned int try, baud, altbaud = 38400;
	upf_t flags = port->flags & UPF_SPD_MASK;

	if (flags == UPF_SPD_HI)
		altbaud = 57600;
	if (flags == UPF_SPD_VHI)
		altbaud = 115200;
	if (flags == UPF_SPD_SHI)
		altbaud = 230400;
	if (flags == UPF_SPD_WARP)
		altbaud = 460800;

	for (try = 0; try < 2; try++) {
		baud = tty_termios_baud_rate(termios);

		/*
		 * The spd_hi, spd_vhi, spd_shi, spd_warp kludge...
		 * Die! Die! Die!
		 */
		if (baud == 38400)
			baud = altbaud;

		/*
		 * Special case: B0 rate.
		 */
		if (baud == 0)
			baud = 9600;

		if (baud >= min && baud <= max)
			return baud;

		/*
		 * Oops, the quotient was zero.  Try again with
		 * the old baud rate if possible.
		 */
		termios->c_cflag &= ~CBAUD;
		if (old) {
			termios->c_cflag |= old->c_cflag & CBAUD;
			old = NULL;
			continue;
		}

		/*
		 * As a last resort, if the quotient is zero,
		 * default to 9600 bps
		 */
		termios->c_cflag |= B9600;
	}

	return 0;
}

EXPORT_SYMBOL(uart_get_baud_rate);

/**
 *	uart_get_divisor - return uart clock divisor
 *	@port: uart_port structure describing the port.
 *	@baud: desired baud rate
 *
 *	Calculate the uart clock divisor for the port.
 */
unsigned int
uart_get_divisor(struct uart_port *port, unsigned int baud)
{
	unsigned int quot;

	/*
	 * Old custom speed handling.
	 */
	if (baud == 38400 && (port->flags & UPF_SPD_MASK) == UPF_SPD_CUST)
		quot = port->custom_divisor;
	else
		quot = (port->uartclk + (8 * baud)) / (16 * baud);

	return quot;
}

EXPORT_SYMBOL(uart_get_divisor);

static void
uart_change_speed(struct uart_state *state, struct termios *old_termios)
{
	struct tty_struct *tty = state->info->tty;
	struct uart_port *port = state->port;
	struct termios *termios;

	/*
	 * If we have no tty, termios, or the port does not exist,
	 * then we can't set the parameters for this port.
	 */
	if (!tty || !tty->termios || port->type == PORT_UNKNOWN)
		return;

	termios = tty->termios;

	/*
	 * Set flags based on termios cflag
	 */
	if (termios->c_cflag & CRTSCTS)
		state->info->flags |= UIF_CTS_FLOW;
	else
		state->info->flags &= ~UIF_CTS_FLOW;

	if (termios->c_cflag & CLOCAL)
		state->info->flags &= ~UIF_CHECK_CD;
	else
		state->info->flags |= UIF_CHECK_CD;

	port->ops->set_termios(port, termios, old_termios);
}

static inline void
__uart_put_char(struct uart_port *port, struct circ_buf *circ, unsigned char c)
{
	unsigned long flags;

	if (!circ->buf)
		return;

	spin_lock_irqsave(&port->lock, flags);
	if (uart_circ_chars_free(circ) != 0) {
		circ->buf[circ->head] = c;
		circ->head = (circ->head + 1) & (UART_XMIT_SIZE - 1);
	}
	spin_unlock_irqrestore(&port->lock, flags);
}

static void uart_put_char(struct tty_struct *tty, unsigned char ch)
{
	struct uart_state *state = tty->driver_data;

	__uart_put_char(state->port, &state->info->xmit, ch);
}

static void uart_flush_chars(struct tty_struct *tty)
{
	uart_start(tty);
}

static int
uart_write(struct tty_struct *tty, const unsigned char *buf, int count)
{
	struct uart_state *state = tty->driver_data;
	struct uart_port *port;
	struct circ_buf *circ;
	unsigned long flags;
	int c, ret = 0;

	/*
	 * This means you called this function _after_ the port was
	 * closed.  No cookie for you.
	 */
	if (!state || !state->info) {
		WARN_ON(1);
		return -EL3HLT;
	}

	port = state->port;
	circ = &state->info->xmit;

	if (!circ->buf)
		return 0;

	spin_lock_irqsave(&port->lock, flags);
	while (1) {
		c = CIRC_SPACE_TO_END(circ->head, circ->tail, UART_XMIT_SIZE);
		if (count < c)
			c = count;
		if (c <= 0)
			break;
		memcpy(circ->buf + circ->head, buf, c);
		circ->head = (circ->head + c) & (UART_XMIT_SIZE - 1);
		buf += c;
		count -= c;
		ret += c;
	}
	spin_unlock_irqrestore(&port->lock, flags);

	uart_start(tty);
	return ret;
}

static int uart_write_room(struct tty_struct *tty)
{
	struct uart_state *state = tty->driver_data;

	return uart_circ_chars_free(&state->info->xmit);
}

static int uart_chars_in_buffer(struct tty_struct *tty)
{
	struct uart_state *state = tty->driver_data;

	return uart_circ_chars_pending(&state->info->xmit);
}

static void uart_flush_buffer(struct tty_struct *tty)
{
	struct uart_state *state = tty->driver_data;
	struct uart_port *port = state->port;
	unsigned long flags;

	/*
	 * This means you called this function _after_ the port was
	 * closed.  No cookie for you.
	 */
	if (!state || !state->info) {
		WARN_ON(1);
		return;
	}

	DPRINTK("uart_flush_buffer(%d) called\n", tty->index);

	spin_lock_irqsave(&port->lock, flags);
	uart_circ_clear(&state->info->xmit);
	spin_unlock_irqrestore(&port->lock, flags);
	tty_wakeup(tty);
}

/*
 * This function is used to send a high-priority XON/XOFF character to
 * the device
 */
static void uart_send_xchar(struct tty_struct *tty, char ch)
{
	struct uart_state *state = tty->driver_data;
	struct uart_port *port = state->port;
	unsigned long flags;

	if (port->ops->send_xchar)
		port->ops->send_xchar(port, ch);
	else {
		port->x_char = ch;
		if (ch) {
			spin_lock_irqsave(&port->lock, flags);
			port->ops->start_tx(port);
			spin_unlock_irqrestore(&port->lock, flags);
		}
	}
}

static void uart_throttle(struct tty_struct *tty)
{
	struct uart_state *state = tty->driver_data;

	if (I_IXOFF(tty))
		uart_send_xchar(tty, STOP_CHAR(tty));

	if (tty->termios->c_cflag & CRTSCTS)
		uart_clear_mctrl(state->port, TIOCM_RTS);
}