generic_serial.c

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/*
 *  generic_serial.c
 *
 *  Copyright (C) 1998/1999 [e-mail]
 *
 *  written for the SX serial driver.
 *     Contains the code that should be shared over all the serial drivers.
 *
 *  Credit for the idea to do it this way might go to Alan Cox. 
 *
 *
 *  Version 0.1 -- December, 1998. Initial version.
 *  Version 0.2 -- March, 1999.    Some more routines. Bugfixes. Etc.
 *  Version 0.5 -- August, 1999.   Some more fixes. Reformat for Linus.
 *
 *  BitWizard is actively maintaining this file. We sometimes find
 *  that someone submitted changes to this file. We really appreciate
 *  your help, but please submit changes through us. We're doing our
 *  best to be responsive.  -- REW
 * */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/tty.h>
#include <linux/serial.h>
#include <linux/mm.h>
#include <linux/generic_serial.h>
#include <asm/semaphore.h>
#include <asm/uaccess.h>

#define DEBUG 

static char *                  tmp_buf; 
static DECLARE_MUTEX(tmp_buf_sem);

static int gs_debug;

#ifdef DEBUG
#define gs_dprintk(f, str...) if (gs_debug & f) printk (str)
#else
#define gs_dprintk(f, str...) /* nothing */
#endif

#define func_enter() gs_dprintk (GS_DEBUG_FLOW, "gs: enter " __FUNCTION__ "\n")
#define func_exit()  gs_dprintk (GS_DEBUG_FLOW, "gs: exit  " __FUNCTION__ "\n")

#if NEW_WRITE_LOCKING
#define DECL      /* Nothing */
#define LOCKIT    down (& port->port_write_sem);
#define RELEASEIT up (&port->port_write_sem);
#else
#define DECL      unsigned long flags;
#define LOCKIT    save_flags (flags);cli ()
#define RELEASEIT restore_flags (flags)
#endif

#define RS_EVENT_WRITE_WAKEUP	1

MODULE_PARM(gs_debug, "i");


void gs_put_char(struct tty_struct * tty, unsigned char ch)
{
	struct gs_port *port;
	DECL

	func_enter (); 

	if (!tty) return;

	port = tty->driver_data;

	if (!port) return;

	if (! (port->flags & ASYNC_INITIALIZED)) return;

	/* Take a lock on the serial tranmit buffer! */
	LOCKIT;

	if (port->xmit_cnt >= SERIAL_XMIT_SIZE - 1) {
		/* Sorry, buffer is full, drop character. Update statistics???? -- REW */
		RELEASEIT;
		return;
	}

	port->xmit_buf[port->xmit_head++] = ch;
	port->xmit_head &= SERIAL_XMIT_SIZE - 1;
	port->xmit_cnt++;  /* Characters in buffer */

	RELEASEIT;
	func_exit ();
}


#ifdef NEW_WRITE_LOCKING

/*
> Problems to take into account are:
>       -1- Interrupts that empty part of the buffer.
>       -2- page faults on the access to userspace. 
>       -3- Other processes that are also trying to do a "write". 
*/

int gs_write(struct tty_struct * tty, int from_user, 
                    const unsigned char *buf, int count)
{
	struct gs_port *port;
	int c, total = 0;
	int t;

	func_enter ();

	if (!tty) return 0;

	port = tty->driver;

	if (!port) return 0;

	if (! (port->flags & ASYNC_INITIALIZED))
		return 0;

	/* get exclusive "write" access to this port (problem 3) */
	/* This is not a spinlock because we can have a disk access (page 
		 fault) in copy_from_user */
	down (& port->port_write_sem);

	while (1) {

		c = count;
 
		/* This is safe because we "OWN" the "head". Noone else can 
		   change the "head": we own the port_write_sem. */
		/* Don't overrun the end of the buffer */
		t = SERIAL_XMIT_SIZE - port->xmit_head;
		if (t < c) c = t;
 
		/* This is safe because the xmit_cnt can only decrease. This 
		   would increase "t", so we might copy too little chars. */
		/* Don't copy past the "head" of the buffer */
		t = SERIAL_XMIT_SIZE - 1 - port->xmit_cnt;
		if (t < c) c = t;
 
		/* Can't copy more? break out! */
		if (c <= 0) break;
		if (from_user)
			copy_from_user (port->xmit_buf + port->xmit_head, buf, c);
		else
			memcpy         (port->xmit_buf + port->xmit_head, buf, c);

		port -> xmit_cnt += c;
		port -> xmit_head = (port->xmit_head + c) & (SERIAL_XMIT_SIZE -1);
		buf += c;
		count -= c;
		total += c;
	}
	up (& port->port_write_sem);

	gs_dprintk (GS_DEBUG_WRITE, "write: interrupts are %s\n", 
	            (port->flags & GS_TX_INTEN)?"enabled": "disabled"); 

	if (port->xmit_cnt && 
	    !tty->stopped && 
	    !tty->hw_stopped &&
	    !(port->flags & GS_TX_INTEN)) {
		port->flags |= GS_TX_INTEN;
		port->rd->enable_tx_interrupts (port);
	}
	func_exit ();
	return total;
}
#else
/*
> Problems to take into account are:
>       -1- Interrupts that empty part of the buffer.
>       -2- page faults on the access to userspace. 
>       -3- Other processes that are also trying to do a "write". 
*/

int gs_write(struct tty_struct * tty, int from_user, 
                    const unsigned char *buf, int count)
{
	struct gs_port *port;
	int c, total = 0;
	int t;
	unsigned long flags;

	func_enter ();

	/* The standard serial driver returns 0 in this case. 
	   That sounds to me as "No error, I just didn't get to writing any
	   bytes. Feel free to try again." 
	   The "official" way to write n bytes from buf is:

		 for (nwritten = 0;nwritten < n;nwritten += rv) {
			 rv = write (fd, buf+nwritten, n-nwritten);
			 if (rv < 0) break; // Error: bail out. //
		 } 

	   which will loop endlessly in this case. The manual page for write
	   agrees with me. In practise almost everybody writes 
	   "write (fd, buf,n);" but some people might have had to deal with 
	   incomplete writes in the past and correctly implemented it by now... 
	 */

	if (!tty) return -EIO;

	port = tty->driver_data;
	if (!port || !port->xmit_buf || !tmp_buf)
		return -EIO;

	save_flags(flags);
	if (from_user) {
		down(&tmp_buf_sem);
		while (1) {
			c = count;

			/* This is safe because we "OWN" the "head". Noone else can 
			   change the "head": we own the port_write_sem. */
			/* Don't overrun the end of the buffer */
			t = SERIAL_XMIT_SIZE - port->xmit_head;
			if (t < c) c = t;
 
			/* This is safe because the xmit_cnt can only decrease. This 
			   would increase "t", so we might copy too little chars. */
			/* Don't copy past the "head" of the buffer */
			t = SERIAL_XMIT_SIZE - 1 - port->xmit_cnt;
			if (t < c) c = t;	 

			/* Can't copy more? break out! */
			if (c <= 0) break;

			c -= copy_from_user(tmp_buf, buf, c);
			if (!c) {
				if (!total)
					total = -EFAULT;
				break;
			}
			cli();
			t = SERIAL_XMIT_SIZE - port->xmit_head;
			if (t < c) c = t;
			t = SERIAL_XMIT_SIZE - 1 - port->xmit_cnt;
			if (t < c) c = t;

			memcpy(port->xmit_buf + port->xmit_head, tmp_buf, c);
			port->xmit_head = ((port->xmit_head + c) &
			                   (SERIAL_XMIT_SIZE-1));
			port->xmit_cnt += c;
			restore_flags(flags);
			buf += c;
			count -= c;
			total += c;
		}
		up(&tmp_buf_sem);
	} else {
		while (1) {
			cli();
			c = count;

			/* This is safe because we "OWN" the "head". Noone else can 
			   change the "head": we own the port_write_sem. */
			/* Don't overrun the end of the buffer */
			t = SERIAL_XMIT_SIZE - port->xmit_head;
			if (t < c) c = t;
 
			/* This is safe because the xmit_cnt can only decrease. This 
			   would increase "t", so we might copy too little chars. */
			/* Don't copy past the "head" of the buffer */
			t = SERIAL_XMIT_SIZE - 1 - port->xmit_cnt;
			if (t < c) c = t;
 
			/* Can't copy more? break out! */
			if (c <= 0) {
				restore_flags(flags);
				break;
			}
			memcpy(port->xmit_buf + port->xmit_head, buf, c);
			port->xmit_head = ((port->xmit_head + c) &
			                   (SERIAL_XMIT_SIZE-1));
			port->xmit_cnt += c;
			restore_flags(flags);
			buf += c;
			count -= c;
			total += c;
		}
	}

	if (port->xmit_cnt && 
	    !tty->stopped && 
	    !tty->hw_stopped &&
	    !(port->flags & GS_TX_INTEN)) {
		port->flags |= GS_TX_INTEN;
		port->rd->enable_tx_interrupts (port);
	}
	func_exit ();
	return total;
}

#endif



int gs_write_room(struct tty_struct * tty)
{
	struct gs_port *port = tty->driver_data;
	int ret;

	func_enter ();
	ret = SERIAL_XMIT_SIZE - port->xmit_cnt - 1;
	if (ret < 0)
		ret = 0;
	func_exit ();
	return ret;
}


int gs_chars_in_buffer(struct tty_struct *tty)
{
	struct gs_port *port = tty->driver_data;
	func_enter ();

	func_exit ();
	return port->xmit_cnt;
}


int gs_real_chars_in_buffer(struct tty_struct *tty)
{
	struct gs_port *port;
	func_enter ();

	if (!tty) return 0;
	port = tty->driver_data;

	if (!port->rd) return 0;
	if (!port->rd->chars_in_buffer) return 0;

	func_exit ();
	return port->xmit_cnt + port->rd->chars_in_buffer (port);
}


static int gs_wait_tx_flushed (void * ptr, int timeout) 
{
	struct gs_port *port = ptr;
	long end_jiffies;
	int jiffies_to_transmit, charsleft = 0, rv = 0;
	int to, rcib;

	func_enter();

	gs_dprintk (GS_DEBUG_FLUSH, "port=%p.\n", port);
	if (port) {
		gs_dprintk (GS_DEBUG_FLUSH, "xmit_cnt=%x, xmit_buf=%p, tty=%p.\n", 
		port->xmit_cnt, port->xmit_buf, port->tty);
	}

	if (!port || port->xmit_cnt < 0 || !port->xmit_buf) {
		gs_dprintk (GS_DEBUG_FLUSH, "ERROR: !port, !port->xmit_buf or prot->xmit_cnt < 0.\n");
		func_exit();
		return -EINVAL;  /* This is an error which we don't know how to handle. */
	}

	rcib = gs_real_chars_in_buffer(port->tty);

	if(rcib <= 0) {
		gs_dprintk (GS_DEBUG_FLUSH, "nothing to wait for.\n");
		func_exit();
		return rv;
	}
	/* stop trying: now + twice the time it would normally take +  seconds */
	end_jiffies  = jiffies; 
	if (timeout !=  MAX_SCHEDULE_TIMEOUT)
		end_jiffies += port->baud?(2 * rcib * 10 * HZ / port->baud):0;
	end_jiffies += timeout;

	gs_dprintk (GS_DEBUG_FLUSH, "now=%lx, end=%lx (%ld).\n", 
		    jiffies, end_jiffies, end_jiffies-jiffies); 

	to = 100;
	/* the expression is actually jiffies < end_jiffies, but that won't
	   work around the wraparound. Tricky eh? */
	while (to-- &&
	       (charsleft = gs_real_chars_in_buffer (port->tty)) &&
	        time_after (end_jiffies, jiffies)) {
		/* Units check: 
		   chars * (bits/char) * (jiffies /sec) / (bits/sec) = jiffies!
		   check! */

		charsleft += 16; /* Allow 16 chars more to be transmitted ... */
		jiffies_to_transmit = port->baud?(1 + charsleft * 10 * HZ / port->baud):0;
		/*                                ^^^ Round up.... */
		if (jiffies_to_transmit <= 0) jiffies_to_transmit = 1;

		gs_dprintk (GS_DEBUG_FLUSH, "Expect to finish in %d jiffies "
			    "(%d chars).\n", jiffies_to_transmit, charsleft); 

		set_current_state (TASK_INTERRUPTIBLE);
		schedule_timeout(jiffies_to_transmit);
		if (signal_pending (current)) {
			gs_dprintk (GS_DEBUG_FLUSH, "Signal pending. Bombing out: "); 
			rv = -EINTR;
			break;
		}
	}

	gs_dprintk (GS_DEBUG_FLUSH, "charsleft = %d.\n", charsleft); 
	set_current_state (TASK_RUNNING);

	func_exit();
	return rv;
}



void gs_flush_buffer(struct tty_struct *tty)
{
	struct gs_port *port;
	unsigned long flags;

	func_enter ();

	if (!tty) return;

	port = tty->driver_data;

	if (!port) return;

	/* XXX Would the write semaphore do? */
	save_flags(flags); cli();
	port->xmit_cnt = port->xmit_head = port->xmit_tail = 0;
	restore_flags(flags);

	wake_up_interruptible(&tty->write_wait);
	if ((tty->flags & (1 << TTY_DO_WRITE_WAKEUP)) &&
	    tty->ldisc.write_wakeup)
		(tty->ldisc.write_wakeup)(tty);
	func_exit ();
}


void gs_flush_chars(struct tty_struct * tty)
{
	struct gs_port *port;

	func_enter ();

	if (!tty) return;

	port = tty->driver_data;

	if (!port) return;

	if (port->xmit_cnt <= 0 || tty->stopped || tty->hw_stopped ||
	    !port->xmit_buf) {
		func_exit ();
		return;
	}

	/* Beats me -- REW */
	port->flags |= GS_TX_INTEN;
	port->rd->enable_tx_interrupts (port);
	func_exit ();
}


void gs_stop(struct tty_struct * tty)
{
	struct gs_port *port;

	func_enter ();

	if (!tty) return;

	port = tty->driver_data;

	if (!port) return;

	if (port->xmit_cnt && 
	    port->xmit_buf && 
	    (port->flags & GS_TX_INTEN) ) {
		port->flags &= ~GS_TX_INTEN;
		port->rd->disable_tx_interrupts (port);
	}
	func_exit ();
}


void gs_start(struct tty_struct * tty)
{
	struct gs_port *port;

	if (!tty) return;

	port = tty->driver_data;

	if (!port) return;

	if (port->xmit_cnt && 
	    port->xmit_buf && 
	    !(port->flags & GS_TX_INTEN) ) {
		port->flags |= GS_TX_INTEN;
		port->rd->enable_tx_interrupts (port);
	}
	func_exit ();
}


void gs_shutdown_port (struct gs_port *port)
{
	long flags;

	func_enter();
	
	if (!port) return;
	
	if (!(port->flags & ASYNC_INITIALIZED))
		return;

	save_flags (flags);
	cli ();

	if (port->xmit_buf) {
		free_page((unsigned long) port->xmit_buf);
		port->xmit_buf = 0;
	}

	if (port->tty)
		set_bit(TTY_IO_ERROR, &port->tty->flags);

	port->rd->shutdown_port (port);

	port->flags &= ~ASYNC_INITIALIZED;
	restore_flags (flags);

	func_exit();
}


void gs_hangup(struct tty_struct *tty)
{