8250.c

the attached file is the driver of Uart

	struct tty_struct *tty = up->port.info->tty;
	unsigned char ch, lsr = *status;
	int max_count = 256;
	char flag;

	do {
		/* The following is not allowed by the tty layer and
		   unsafe. It should be fixed ASAP */
		if (unlikely(tty->flip.count >= TTY_FLIPBUF_SIZE)) {
			if (tty->low_latency) {
				spin_unlock(&up->port.lock);
				tty_flip_buffer_push(tty);
				spin_lock(&up->port.lock);
			}
			/* If this failed then we will throw away the
			   bytes but must do so to clear interrupts */
		}
		ch = serial_inp(up, UART_RX);
		flag = TTY_NORMAL;
		up->port.icount.rx++;

#ifdef CONFIG_SERIAL_8250_CONSOLE
		/*
		 * Recover the break flag from console xmit
		 */
		if (up->port.line == up->port.cons->index) {
			lsr |= up->lsr_break_flag;
			up->lsr_break_flag = 0;
		}
#endif

		if (unlikely(lsr & (UART_LSR_BI | UART_LSR_PE |
				    UART_LSR_FE | UART_LSR_OE))) {
			/*
			 * For statistics only
			 */
			if (lsr & UART_LSR_BI) {
				lsr &= ~(UART_LSR_FE | UART_LSR_PE);
				up->port.icount.brk++;
				/*
				 * We do the SysRQ and SAK checking
				 * here because otherwise the break
				 * may get masked by ignore_status_mask
				 * or read_status_mask.
				 */
				if (uart_handle_break(&up->port))
					goto ignore_char;
			} else if (lsr & UART_LSR_PE)
				up->port.icount.parity++;
			else if (lsr & UART_LSR_FE)
				up->port.icount.frame++;
			if (lsr & UART_LSR_OE)
				up->port.icount.overrun++;

			/*
			 * Mask off conditions which should be ingored.
			 */
			lsr &= up->port.read_status_mask;

			if (lsr & UART_LSR_BI) {
				DEBUG_INTR("handling break....");
				flag = TTY_BREAK;
			} else if (lsr & UART_LSR_PE)
				flag = TTY_PARITY;
			else if (lsr & UART_LSR_FE)
				flag = TTY_FRAME;
		}
		if (uart_handle_sysrq_char(&up->port, ch, regs))
			goto ignore_char;
		if ((lsr & up->port.ignore_status_mask) == 0) {
			tty_insert_flip_char(tty, ch, flag);
		}
		if ((lsr & UART_LSR_OE) &&
		    tty->flip.count < TTY_FLIPBUF_SIZE) {
			/*
			 * Overrun is special, since it's reported
			 * immediately, and doesn't affect the current
			 * character.
			 */
			tty_insert_flip_char(tty, 0, TTY_OVERRUN);
		}
	ignore_char:
		lsr = serial_inp(up, UART_LSR);
	} while ((lsr & UART_LSR_DR) && (max_count-- > 0));
	spin_unlock(&up->port.lock);
	tty_flip_buffer_push(tty);
	spin_lock(&up->port.lock);
	*status = lsr;
}

static _INLINE_ void transmit_chars(struct uart_8250_port *up)
{
	struct circ_buf *xmit = &up->port.info->xmit;
	int count;

	if (up->port.x_char) {
		serial_outp(up, UART_TX, up->port.x_char);
		up->port.icount.tx++;
		up->port.x_char = 0;
		return;
	}
	if (uart_circ_empty(xmit) || uart_tx_stopped(&up->port)) {
		serial8250_stop_tx(&up->port, 0);
		return;
	}

	count = up->tx_loadsz;
	do {
		serial_out(up, UART_TX, xmit->buf[xmit->tail]);
		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
		up->port.icount.tx++;
		if (uart_circ_empty(xmit))
			break;
	} while (--count > 0);

	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
		uart_write_wakeup(&up->port);

	DEBUG_INTR("THRE...");

	if (uart_circ_empty(xmit))
		serial8250_stop_tx(&up->port, 0);
}

static _INLINE_ void check_modem_status(struct uart_8250_port *up)
{
	int status;

	status = serial_in(up, UART_MSR);

	if ((status & UART_MSR_ANY_DELTA) == 0)
		return;

	if (status & UART_MSR_TERI)
		up->port.icount.rng++;
	if (status & UART_MSR_DDSR)
		up->port.icount.dsr++;
	if (status & UART_MSR_DDCD)
		uart_handle_dcd_change(&up->port, status & UART_MSR_DCD);
	if (status & UART_MSR_DCTS)
		uart_handle_cts_change(&up->port, status & UART_MSR_CTS);

	wake_up_interruptible(&up->port.info->delta_msr_wait);
}

/*
 * This handles the interrupt from one port.
 */
static inline void
serial8250_handle_port(struct uart_8250_port *up, struct pt_regs *regs)
{
	unsigned int status = serial_inp(up, UART_LSR);

	DEBUG_INTR("status = %x...", status);

	if (status & UART_LSR_DR)
		receive_chars(up, &status, regs);
	check_modem_status(up);
	if (status & UART_LSR_THRE)
		transmit_chars(up);
}

/*!
 * This is the 16C652 serial driver's interrupt routine modified for MXC. This
 * function is modified to handle interrupt pin connectivity requirements.
 * 
 * @param   irq      The Interrupt number
 * @param   dev_id   Driver private data
 * @param   regs     Holds a snapshot of the processors context before the
 *                   processor entered the interrupt code
 *
 * @result    This function returns \b IRQ_HANDLED. 
 *            \b IRQ_HANDLED is defined in include/linux/interrupt.h.
 *
 */

/*
 * This is the serial driver's interrupt routine.
 *
 * Arjan thinks the old way was overly complex, so it got simplified.
 * Alan disagrees, saying that need the complexity to handle the weird
 * nature of ISA shared interrupts.  (This is a special exception.)
 *
 * In order to handle ISA shared interrupts properly, we need to check
 * that all ports have been serviced, and therefore the ISA interrupt
 * line has been de-asserted.
 *
 * This means we need to loop through all ports. checking that they
 * don't have an interrupt pending.
 */
static irqreturn_t serial8250_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
	struct irq_info *i = dev_id;
	struct list_head *l, *end = NULL;
	int pass_counter = 0, handled = 0;

	DEBUG_INTR("serial8250_interrupt(%d)...", irq);

	spin_lock(&i->lock);

	l = i->head;
	do {
		struct uart_8250_port *up;
		unsigned int iir;

		up = list_entry(l, struct uart_8250_port, list);

#if defined(CONFIG_ARCH_ARGONPLUS) || \
    defined(CONFIG_ARCH_SCMA11) || \
    defined(CONFIG_ARCH_MX3) || \
    defined(CONFIG_MACH_ZEUSEVB)
		/*
		 * Make sure INTA-B are active in the MCR, otherwise the DUART will
		 * tri-state the INT lines
		 */
		serial_out(up, UART_MCR, serial_inp(up, UART_MCR) | UART_MCR_OUT2);

		/*
		 * Get the EDIO interrupt, clear if set.
		 */
		extuart_intr_clear(up->port.line);
#endif
		iir = serial_in(up, UART_IIR);
		if (!(iir & UART_IIR_NO_INT)) {
			spin_lock(&up->port.lock);
			serial8250_handle_port(up, regs);
			spin_unlock(&up->port.lock);

			handled = 1;

			end = NULL;
		} else if (end == NULL)
			end = l;

		l = l->next;

		if (l == i->head && pass_counter++ > PASS_LIMIT) {
			/* If we hit this, we're dead. */
			printk(KERN_ERR "serial8250: too much work for "
				"irq%d\n", irq);
			break;
		}
	} while (l != end);

	spin_unlock(&i->lock);

	DEBUG_INTR("end.\n");

	//return IRQ_RETVAL(handled);
	return IRQ_HANDLED;	/* FIXME: iir status not ready on 1510 */
}

/*
 * To support ISA shared interrupts, we need to have one interrupt
 * handler that ensures that the IRQ line has been deasserted
 * before returning.  Failing to do this will result in the IRQ
 * line being stuck active, and, since ISA irqs are edge triggered,
 * no more IRQs will be seen.
 */
static void serial_do_unlink(struct irq_info *i, struct uart_8250_port *up)
{
	spin_lock_irq(&i->lock);

	if (!list_empty(i->head)) {
		if (i->head == &up->list)
			i->head = i->head->next;
		list_del(&up->list);
	} else {
		BUG_ON(i->head != &up->list);
		i->head = NULL;
	}

	spin_unlock_irq(&i->lock);
}

/*!
 * This function registers UART interrupt service routine, if not already
 * registered. If Interrupt type flags contains UPF_SHARE_IRQ, interrupt
 * sharing is enabled. This function inserts irq info into irq_lists. This
 * function handles interrupt pin configurations required for MXC boards.
 * 
 * @param   up   the 8250 UART port structure 
 *
 * @result   This function returns zero if irq_lists is already initialized
 *           or the return value from request_irq(). 
 */
static int serial_link_irq_chain(struct uart_8250_port *up)
{
	struct irq_info *i = irq_lists + up->port.irq;
	int ret, irq_flags = up->port.flags & UPF_SHARE_IRQ ? SA_SHIRQ : 0;

	spin_lock_irq(&i->lock);

	if (i->head) {
		list_add(&up->list, i->head);
		spin_unlock_irq(&i->lock);

		ret = 0;
	} else {
		INIT_LIST_HEAD(&up->list);
		i->head = &up->list;
		spin_unlock_irq(&i->lock);

#if defined(CONFIG_ARCH_SCMA11) || \
    defined(CONFIG_ARCH_MX3) || \
    defined(CONFIG_ARCH_ARGONPLUS)
		ret = extuart_intr_setup(up->port.line);
		/*
                 * Register the ISR with the GPIO driver,
                 * return after registering
                 */
		if (ret == 1) {
			ret = gpio_request_irq(2, 30, GPIO_HIGH_PRIO,
					       serial8250_interrupt,
					       irq_flags, "serial", i);
			if (ret != 0) {
				gpio_free_irq(2, 30, GPIO_HIGH_PRIO);
				serial_do_unlink(i, up);
			}
			return ret;
		}
#endif

#if defined(CONFIG_MACH_ZEUSEVB)
		ret = extuart_intr_setup(up->port.line, up->port.irq, serial8250_interrupt,
					 irq_flags, "serial", i);
#else
		ret = request_irq(up->port.irq, serial8250_interrupt,
				  irq_flags, "serial", i);
#endif
		if (ret < 0)
			serial_do_unlink(i, up);
	}

	return ret;
}

static void serial_unlink_irq_chain(struct uart_8250_port *up)
{
	struct irq_info *i = irq_lists + up->port.irq;

	BUG_ON(i->head == NULL);

#if defined(CONFIG_ARCH_ARGONPLUS) || \
    defined(CONFIG_ARCH_SCMA11) || \
    defined(CONFIG_ARCH_MX3)
	if (list_empty(i->head)) {
		if (extuart_intr_cleanup(up->port.line)) {
			gpio_free_irq(2, 30, GPIO_HIGH_PRIO);
		} else {
			free_irq(up->port.irq, i);
		}
		serial_do_unlink(i, up);
		return;
	}
#endif
	if (list_empty(i->head))
#if defined(CONFIG_MACH_ZEUSEVB)
		extuart_intr_cleanup(up->port.line, up->port.irq, i);
#else
		free_irq(up->port.irq, i);
#endif

	serial_do_unlink(i, up);
}

/*
 * This function is used to handle ports that do not have an
 * interrupt.  This doesn't work very well for 16450's, but gives
 * barely passable results for a 16550A.  (Although at the expense
 * of much CPU overhead).
 */
static void serial8250_timeout(unsigned long data)
{
	struct uart_8250_port *up = (struct uart_8250_port *)data;
	unsigned int timeout;
	unsigned int iir;

	iir = serial_in(up, UART_IIR);
	if (!(iir & UART_IIR_NO_INT)) {
		spin_lock(&up->port.lock);
		serial8250_handle_port(up, NULL);
		spin_unlock(&up->port.lock);
	}

	timeout = up->port.timeout;
	timeout = timeout > 6 ? (timeout / 2 - 2) : 1;
	mod_timer(&up->timer, jiffies + timeout);
}

static unsigned int serial8250_tx_empty(struct uart_port *port)
{
	struct uart_8250_port *up = (struct uart_8250_port *)port;
	unsigned long flags;
	unsigned int ret;

	spin_lock_irqsave(&up->port.lock, flags);
	ret = serial_in(up, UART_LSR) & UART_LSR_TEMT ? TIOCSER_TEMT : 0;
	spin_unlock_irqrestore(&up->port.lock, flags);

	return ret;
}

static unsigned int serial8250_get_mctrl(struct uart_port *port)
{
	struct uart_8250_port *up = (struct uart_8250_port *)port;
	unsigned long flags;
	unsigned char status;
	unsigned int ret;

	spin_lock_irqsave(&up->port.lock, flags);
	status = serial_in(up, UART_MSR);
	spin_unlock_irqrestore(&up->port.lock, flags);

	ret = 0;
	if (status & UART_MSR_DCD)
		ret |= TIOCM_CAR;
	if (status & UART_MSR_RI)
		ret |= TIOCM_RNG;
	if (status & UART_MSR_DSR)
		ret |= TIOCM_DSR;
	if (status & UART_MSR_CTS)
		ret |= TIOCM_CTS;
	return ret;
}

static void serial8250_set_mctrl(struct uart_port *port, unsigned int mctrl)
{
	struct uart_8250_port *up = (struct uart_8250_port *)port;
	unsigned char mcr = 0;

	if (mctrl & TIOCM_RTS)
		mcr |= UART_MCR_RTS;
	if (mctrl & TIOCM_DTR)
		mcr |= UART_MCR_DTR;
	if (mctrl & TIOCM_OUT1)
		mcr |= UART_MCR_OUT1;
	if (mctrl & TIOCM_OUT2)
		mcr |= UART_MCR_OUT2;
	if (mctrl & TIOCM_LOOP)
		mcr |= UART_MCR_LOOP;

	mcr = (mcr & up->mcr_mask) | up->mcr_force | up->mcr;

	serial_out(up, UART_MCR, mcr);
}

static void serial8250_break_ctl(struct uart_port *port, int break_state)
{
	struct uart_8250_port *up = (struct uart_8250_port *)port;
	unsigned long flags;

	spin_lock_irqsave(&up->port.lock, flags);
	if (break_state == -1)
		up->lcr |= UART_LCR_SBC;
	else
		up->lcr &= ~UART_LCR_SBC;
	serial_out(up, UART_LCR, up->lcr);
	spin_unlock_irqrestore(&up->port.lock, flags);
}

static int serial8250_startup(struct uart_port *port)
{
	struct uart_8250_port *up = (struct uart_8250_port *)port;
	unsigned long flags;
	int retval;

	if (up->port.line == kgdb8250_ttyS)
		return -EBUSY;

	up->capabilities = uart_config[up->port.type].flags;
	up->mcr = 0;

	if (up->port.type == PORT_16C950) {
		/* Wake up and initialize UART */
		up->acr = 0;
		serial_outp(up, UART_LCR, 0xBF);
		serial_outp(up, UART_EFR, UART_EFR_ECB);
		serial_outp(up, UART_IER, 0);
		serial_outp(up, UART_LCR, 0);
		serial_icr_write(up, UART_CSR, 0); /* Reset the UART */
		serial_outp(up, UART_LCR, 0xBF);
		serial_outp(up, UART_EFR, UART_EFR_ECB);
		serial_outp(up, UART_LCR, 0);
	}

#ifdef CONFIG_SERIAL_8250_RSA
	/*
	 * If this is an RSA port, see if we can kick it up to the
	 * higher speed clock.
	 */
	enable_rsa(up);
#endif

	/*
	 * Clear the FIFO buffers and disable them.
	 * (they will be reeanbled in set_termios())
	 */
	serial8250_clear_fifos(up);

	/*
	 * Clear the interrupt registers.
	 */
	(void) serial_inp(up, UART_LSR);
	(void) serial_inp(up, UART_RX);
	(void) serial_inp(up, UART_IIR);
	(void) serial_inp(up, UART_MSR);

	/*
	 * At this point, there's no way the LSR could still be 0xff;
	 * if it is, then bail out, because there's likely no UART
	 * here.
	 */