path: root/drivers/char/generic_serial.c

/*
 *  generic_serial.c
 *
 *  Copyright (C) 1998/1999 R.E.Wolff@BitWizard.nl
 *
 *  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 <linux/interrupt.h>
#include <linux/tty_flip.h>
#include <linux/delay.h>
#include <asm/semaphore.h>
#include <asm/uaccess.h>

#define DEBUG 

static char *                  tmp_buf; 

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 %s\n", __FUNCTION__)
#define func_exit()  gs_dprintk (GS_DEBUG_FLOW, "gs: exit  %s\n", __FUNCTION__)
#define NEW_WRITE_LOCKING 1
#if NEW_WRITE_LOCKING
#define DECL      /* Nothing */
#define LOCKIT    mutex_lock(& port->port_write_mutex);
#define RELEASEIT mutex_unlock(&port->port_write_mutex);
#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_param(gs_debug, int, 0644);


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, 
                    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_data;

	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 */
	mutex_lock(& port->port_write_mutex);

	while (1) {

		c = count;
 
		/* This is safe because we "OWN" the "head". Noone else can 
		   change the "head": we own the port_write_mutex. */
		/* 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;

		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;
	}
	mutex_unlock(& port->port_write_mutex);

	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,
                    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. //
		 } <