drivers/s390/char/sclp_tty.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  *    SCLP line mode terminal driver.
  *
  *  S390 version
  *    Copyright IBM Corp. 1999
  *    Author(s): Martin Peschke <mpeschke@de.ibm.com>
  *		 Martin Schwidefsky <schwidefsky@de.ibm.com>
  */

 #include <linux/kmod.h>
 #include <linux/tty.h>
 #include <linux/tty_driver.h>
 #include <linux/tty_flip.h>
 #include <linux/err.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/gfp.h>
 #include <linux/uaccess.h>

 #include "ctrlchar.h"
 #include "sclp.h"
 #include "sclp_rw.h"
 #include "sclp_tty.h"

 /*
  * size of a buffer that collects single characters coming in
  * via sclp_tty_put_char()
  */
 #define SCLP_TTY_BUF_SIZE 512

 /*
  * There is exactly one SCLP terminal, so we can keep things simple
  * and allocate all variables statically.
  */

 /* Lock to guard over changes to global variables. */
 static spinlock_t sclp_tty_lock;
 /* List of free pages that can be used for console output buffering. */
 static struct list_head sclp_tty_pages;
 /* List of full struct sclp_buffer structures ready for output. */
 static struct list_head sclp_tty_outqueue;
 /* Counter how many buffers are emitted. */
 static int sclp_tty_buffer_count;
 /* Pointer to current console buffer. */
 static struct sclp_buffer *sclp_ttybuf;
 /* Timer for delayed output of console messages. */
 static struct timer_list sclp_tty_timer;

 static struct tty_port sclp_port;
 static unsigned char sclp_tty_chars[SCLP_TTY_BUF_SIZE];
 static unsigned short int sclp_tty_chars_count;

 struct tty_driver *sclp_tty_driver;

 static int sclp_tty_tolower;
 static int sclp_tty_columns = 80;

 #define SPACES_PER_TAB 8
 #define CASE_DELIMITER 0x6c /* to separate upper and lower case (% in EBCDIC) */

 /* This routine is called whenever we try to open a SCLP terminal. */
 static int
 sclp_tty_open(struct tty_struct *tty, struct file *filp)
 {
 	tty_port_tty_set(&sclp_port, tty);
 	tty->driver_data = NULL;
 	return 0;
 }

 /* This routine is called when the SCLP terminal is closed. */
 static void
 sclp_tty_close(struct tty_struct *tty, struct file *filp)
 {
 	if (tty->count > 1)
 		return;
 	tty_port_tty_set(&sclp_port, NULL);
 }

 /*
  * This routine returns the numbers of characters the tty driver
  * will accept for queuing to be written.  This number is subject
  * to change as output buffers get emptied, or if the output flow
  * control is acted. This is not an exact number because not every
  * character needs the same space in the sccb. The worst case is
  * a string of newlines. Every newline creates a new message which
  * needs 82 bytes.
  */
 static int
 sclp_tty_write_room (struct tty_struct *tty)
 {
 	unsigned long flags;
 	struct list_head *l;
 	int count;

 	spin_lock_irqsave(&sclp_tty_lock, flags);
 	count = 0;
 	if (sclp_ttybuf != NULL)
 		count = sclp_buffer_space(sclp_ttybuf) / sizeof(struct msg_buf);
 	list_for_each(l, &sclp_tty_pages)
 		count += NR_EMPTY_MSG_PER_SCCB;
 	spin_unlock_irqrestore(&sclp_tty_lock, flags);
 	return count;
 }

 static void
 sclp_ttybuf_callback(struct sclp_buffer *buffer, int rc)
 {
 	unsigned long flags;
 	void *page;

 	do {
 		page = sclp_unmake_buffer(buffer);
 		spin_lock_irqsave(&sclp_tty_lock, flags);
 		/* Remove buffer from outqueue */
 		list_del(&buffer->list);
 		sclp_tty_buffer_count--;
 		list_add_tail((struct list_head *) page, &sclp_tty_pages);
 		/* Check if there is a pending buffer on the out queue. */
 		buffer = NULL;
 		if (!list_empty(&sclp_tty_outqueue))
 			buffer = list_entry(sclp_tty_outqueue.next,
 					    struct sclp_buffer, list);
 		spin_unlock_irqrestore(&sclp_tty_lock, flags);
 	} while (buffer && sclp_emit_buffer(buffer, sclp_ttybuf_callback));

 	tty_port_tty_wakeup(&sclp_port);
 }

 static inline void
 __sclp_ttybuf_emit(struct sclp_buffer *buffer)
 {
 	unsigned long flags;
 	int count;
 	int rc;

 	spin_lock_irqsave(&sclp_tty_lock, flags);
 	list_add_tail(&buffer->list, &sclp_tty_outqueue);
 	count = sclp_tty_buffer_count++;
 	spin_unlock_irqrestore(&sclp_tty_lock, flags);
 	if (count)
 		return;
 	rc = sclp_emit_buffer(buffer, sclp_ttybuf_callback);
 	if (rc)
 		sclp_ttybuf_callback(buffer, rc);
 }

 /*
  * When this routine is called from the timer then we flush the
  * temporary write buffer.
  */
 static void
 sclp_tty_timeout(struct timer_list *unused)
 {
 	unsigned long flags;
 	struct sclp_buffer *buf;

 	spin_lock_irqsave(&sclp_tty_lock, flags);
 	buf = sclp_ttybuf;
 	sclp_ttybuf = NULL;
 	spin_unlock_irqrestore(&sclp_tty_lock, flags);

 	if (buf != NULL) {
 		__sclp_ttybuf_emit(buf);
 	}
 }

 /*
  * Write a string to the sclp tty.
  */
 static int sclp_tty_write_string(const unsigned char *str, int count, int may_fail)
 {
 	unsigned long flags;
 	void *page;
 	int written;
 	int overall_written;
 	struct sclp_buffer *buf;

 	if (count <= 0)
 		return 0;
 	overall_written = 0;
 	spin_lock_irqsave(&sclp_tty_lock, flags);
 	do {
 		/* Create a sclp output buffer if none exists yet */
 		if (sclp_ttybuf == NULL) {
 			while (list_empty(&sclp_tty_pages)) {
 				spin_unlock_irqrestore(&sclp_tty_lock, flags);
 				if (may_fail)
 					goto out;
 				else
 					sclp_sync_wait();
 				spin_lock_irqsave(&sclp_tty_lock, flags);
 			}
 			page = sclp_tty_pages.next;
 			list_del((struct list_head *) page);
 			sclp_ttybuf = sclp_make_buffer(page, sclp_tty_columns,
 						       SPACES_PER_TAB);
 		}
 		/* try to write the string to the current output buffer */
 		written = sclp_write(sclp_ttybuf, str, count);
 		overall_written += written;
 		if (written == count)
 			break;
 		/*
 		 * Not all characters could be written to the current
 		 * output buffer. Emit the buffer, create a new buffer
 		 * and then output the rest of the string.
 		 */
 		buf = sclp_ttybuf;
 		sclp_ttybuf = NULL;
 		spin_unlock_irqrestore(&sclp_tty_lock, flags);
 		__sclp_ttybuf_emit(buf);
 		spin_lock_irqsave(&sclp_tty_lock, flags);
 		str += written;
 		count -= written;
 	} while (count > 0);
 	/* Setup timer to output current console buffer after 1/10 second */
 	if (sclp_ttybuf && sclp_chars_in_buffer(sclp_ttybuf) &&
 	    !timer_pending(&sclp_tty_timer)) {
 		mod_timer(&sclp_tty_timer, jiffies + HZ / 10);
 	}
 	spin_unlock_irqrestore(&sclp_tty_lock, flags);
 out:
 	return overall_written;
 }

 /*
  * This routine is called by the kernel to write a series of characters to the
  * tty device. The characters may come from user space or kernel space. This
  * routine will return the number of characters actually accepted for writing.
  */
 static int
 sclp_tty_write(struct tty_struct *tty, const unsigned char *buf, int count)
 {
 	if (sclp_tty_chars_count > 0) {
 		sclp_tty_write_string(sclp_tty_chars, sclp_tty_chars_count, 0);
 		sclp_tty_chars_count = 0;
 	}
 	return sclp_tty_write_string(buf, count, 1);
 }

 /*
  * This routine is called by the kernel to write a single character to the tty
  * device. If the kernel uses this routine, it must call the flush_chars()
  * routine (if defined) when it is done stuffing characters into the driver.
  *
  * Characters provided to sclp_tty_put_char() are buffered by the SCLP driver.
  * If the given character is a '\n' the contents of the SCLP write buffer
  * - including previous characters from sclp_tty_put_char() and strings from
  * sclp_write() without final '\n' - will be written.
  */
 static int
 sclp_tty_put_char(struct tty_struct *tty, unsigned char ch)
 {
 	sclp_tty_chars[sclp_tty_chars_count++] = ch;
 	if (ch == '\n' || sclp_tty_chars_count >= SCLP_TTY_BUF_SIZE) {
 		sclp_tty_write_string(sclp_tty_chars, sclp_tty_chars_count, 0);
 		sclp_tty_chars_count = 0;
 	}
 	return 1;
 }

 /*
  * This routine is called by the kernel after it has written a series of
  * characters to the tty device using put_char().
  */
 static void
 sclp_tty_flush_chars(struct tty_struct *tty)
 {
 	if (sclp_tty_chars_count > 0) {
 		sclp_tty_write_string(sclp_tty_chars, sclp_tty_chars_count, 0);
 		sclp_tty_chars_count = 0;
 	}
 }

 /*
  * This routine returns the number of characters in the write buffer of the
  * SCLP driver. The provided number includes all characters that are stored
  * in the SCCB (will be written next time the SCLP is not busy) as well as
  * characters in the write buffer (will not be written as long as there is a
  * final line feed missing).
  */
 static int
 sclp_tty_chars_in_buffer(struct tty_struct *tty)
 {
 	unsigned long flags;
 	struct list_head *l;
 	struct sclp_buffer *t;
 	int count;

 	spin_lock_irqsave(&sclp_tty_lock, flags);
 	count = 0;
 	if (sclp_ttybuf != NULL)
 		count = sclp_chars_in_buffer(sclp_ttybuf);
 	list_for_each(l, &sclp_tty_outqueue) {
 		t = list_entry(l, struct sclp_buffer, list);
 		count += sclp_chars_in_buffer(t);
 	}
 	spin_unlock_irqrestore(&sclp_tty_lock, flags);
 	return count;
 }

 /*
  * removes all content from buffers of low level driver
  */
 static void
 sclp_tty_flush_buffer(struct tty_struct *tty)
 {
 	if (sclp_tty_chars_count > 0) {
 		sclp_tty_write_string(sclp_tty_chars, sclp_tty_chars_count, 0);
 		sclp_tty_chars_count = 0;
 	}
 }

 /*
  * push input to tty
  */
 static void
 sclp_tty_input(unsigned char* buf, unsigned int count)
 {
 	struct tty_struct *tty = tty_port_tty_get(&sclp_port);
 	unsigned int cchar;

 	/*
 	 * If this tty driver is currently closed
 	 * then throw the received input away.
 	 */
 	if (tty == NULL)
 		return;
 	cchar = ctrlchar_handle(buf, count, tty);
 	switch (cchar & CTRLCHAR_MASK) {
 	case CTRLCHAR_SYSRQ:
 		break;
 	case CTRLCHAR_CTRL:
 		tty_insert_flip_char(&sclp_port, cchar, TTY_NORMAL);
 		tty_flip_buffer_push(&sclp_port);
 		break;
 	case CTRLCHAR_NONE:
 		/* send (normal) input to line discipline */
 		if (count < 2 ||
 		    (strncmp((const char *) buf + count - 2, "^n", 2) &&
 		     strncmp((const char *) buf + count - 2, "\252n", 2))) {
 			/* add the auto \n */
 			tty_insert_flip_string(&sclp_port, buf, count);
 			tty_insert_flip_char(&sclp_port, '\n', TTY_NORMAL);
 		} else
 			tty_insert_flip_string(&sclp_port, buf, count - 2);
 		tty_flip_buffer_push(&sclp_port);
 		break;
 	}
 	tty_kref_put(tty);
 }

 /*
  * get a EBCDIC string in upper/lower case,
  * find out characters in lower/upper case separated by a special character,
  * modifiy original string,
  * returns length of resulting string
  */
 static int sclp_switch_cases(unsigned char *buf, int count)
 {
 	unsigned char *ip, *op;
 	int toggle;

 	/* initially changing case is off */
 	toggle = 0;
 	ip = op = buf;
 	while (count-- > 0) {
 		/* compare with special character */
 		if (*ip == CASE_DELIMITER) {
 			/* followed by another special character? */
 			if (count && ip[1] == CASE_DELIMITER) {
 				/*
 				 * ... then put a single copy of the special
 				 * character to the output string
 				 */
 				*op++ = *ip++;
 				count--;
 			} else
 				/*
 				 * ... special character follower by a normal
 				 * character toggles the case change behaviour
 				 */
 				toggle = ~toggle;
 			/* skip special character */
 			ip++;
 		} else
 			/* not the special character */
 			if (toggle)
 				/* but case switching is on */
 				if (sclp_tty_tolower)
 					/* switch to uppercase */
 					*op++ = _ebc_toupper[(int) *ip++];
 				else
 					/* switch to lowercase */
 					*op++ = _ebc_tolower[(int) *ip++];
 			else
 				/* no case switching, copy the character */
 				*op++ = *ip++;
 	}
 	/* return length of reformatted string. */
 	return op - buf;
 }

 static void sclp_get_input(struct gds_subvector *sv)
 {
 	unsigned char *str;
 	int count;

 	str = (unsigned char *) (sv + 1);
 	count = sv->length - sizeof(*sv);
 	if (sclp_tty_tolower)
 		EBC_TOLOWER(str, count);
 	count = sclp_switch_cases(str, count);
 	/* convert EBCDIC to ASCII (modify original input in SCCB) */
 	sclp_ebcasc_str(str, count);

 	/* transfer input to high level driver */
 	sclp_tty_input(str, count);
 }

 static inline void sclp_eval_selfdeftextmsg(struct gds_subvector *sv)
 {
 	void *end;

 	end = (void *) sv + sv->length;
 	for (sv = sv + 1; (void *) sv < end; sv = (void *) sv + sv->length)
 		if (sv->key == 0x30)
 			sclp_get_input(sv);
 }

 static inline void sclp_eval_textcmd(struct gds_vector *v)
 {
 	struct gds_subvector *sv;
 	void *end;

 	end = (void *) v + v->length;
 	for (sv = (struct gds_subvector *) (v + 1);
 	     (void *) sv < end; sv = (void *) sv + sv->length)
 		if (sv->key == GDS_KEY_SELFDEFTEXTMSG)
 			sclp_eval_selfdeftextmsg(sv);

 }

 static inline void sclp_eval_cpmsu(struct gds_vector *v)
 {
 	void *end;

 	end = (void *) v + v->length;
 	for (v = v + 1; (void *) v < end; v = (void *) v + v->length)
 		if (v->gds_id == GDS_ID_TEXTCMD)
 			sclp_eval_textcmd(v);
 }


 static inline void sclp_eval_mdsmu(struct gds_vector *v)
 {
 	v = sclp_find_gds_vector(v + 1, (void *) v + v->length, GDS_ID_CPMSU);
 	if (v)
 		sclp_eval_cpmsu(v);
 }

 static void sclp_tty_receiver(struct evbuf_header *evbuf)
 {
 	struct gds_vector *v;

 	v = sclp_find_gds_vector(evbuf + 1, (void *) evbuf + evbuf->length,
 				 GDS_ID_MDSMU);
 	if (v)
 		sclp_eval_mdsmu(v);
 }

 static void
 sclp_tty_state_change(struct sclp_register *reg)
 {
 }

 static struct sclp_register sclp_input_event =
 {
 	.receive_mask = EVTYP_OPCMD_MASK | EVTYP_PMSGCMD_MASK,
 	.state_change_fn = sclp_tty_state_change,
 	.receiver_fn = sclp_tty_receiver
 };

 static const struct tty_operations sclp_ops = {
 	.open = sclp_tty_open,
 	.close = sclp_tty_close,
 	.write = sclp_tty_write,
 	.put_char = sclp_tty_put_char,
 	.flush_chars = sclp_tty_flush_chars,
 	.write_room = sclp_tty_write_room,
 	.chars_in_buffer = sclp_tty_chars_in_buffer,
 	.flush_buffer = sclp_tty_flush_buffer,
 };

 static int __init
 sclp_tty_init(void)
 {
 	struct tty_driver *driver;
 	void *page;
 	int i;
 	int rc;

 	/* z/VM multiplexes the line mode output on the 32xx screen */
 	if (MACHINE_IS_VM && !CONSOLE_IS_SCLP)
 		return 0;
 	if (!sclp.has_linemode)
 		return 0;
 	driver = alloc_tty_driver(1);
 	if (!driver)
 		return -ENOMEM;

 	rc = sclp_rw_init();
 	if (rc) {
 		put_tty_driver(driver);
 		return rc;
 	}
 	/* Allocate pages for output buffering */
 	INIT_LIST_HEAD(&sclp_tty_pages);
 	for (i = 0; i < MAX_KMEM_PAGES; i++) {
 		page = (void *) get_zeroed_page(GFP_KERNEL | GFP_DMA);
 		if (page == NULL) {
 			put_tty_driver(driver);
 			return -ENOMEM;
 		}
 		list_add_tail((struct list_head *) page, &sclp_tty_pages);
 	}
 	INIT_LIST_HEAD(&sclp_tty_outqueue);
 	spin_lock_init(&sclp_tty_lock);
 	timer_setup(&sclp_tty_timer, sclp_tty_timeout, 0);
 	sclp_ttybuf = NULL;
 	sclp_tty_buffer_count = 0;
 	if (MACHINE_IS_VM) {
 		/*
 		 * save 4 characters for the CPU number
 		 * written at start of each line by VM/CP
 		 */
 		sclp_tty_columns = 76;
 		/* case input lines to lowercase */
 		sclp_tty_tolower = 1;
 	}
 	sclp_tty_chars_count = 0;

 	rc = sclp_register(&sclp_input_event);
 	if (rc) {
 		put_tty_driver(driver);
 		return rc;
 	}

 	tty_port_init(&sclp_port);

 	driver->driver_name = "sclp_line";
 	driver->name = "sclp_line";
 	driver->major = TTY_MAJOR;
 	driver->minor_start = 64;
 	driver->type = TTY_DRIVER_TYPE_SYSTEM;
 	driver->subtype = SYSTEM_TYPE_TTY;
 	driver->init_termios = tty_std_termios;
 	driver->init_termios.c_iflag = IGNBRK | IGNPAR;
 	driver->init_termios.c_oflag = ONLCR;
 	driver->init_termios.c_lflag = ISIG | ECHO;
 	driver->flags = TTY_DRIVER_REAL_RAW;
 	tty_set_operations(driver, &sclp_ops);
 	tty_port_link_device(&sclp_port, driver, 0);
 	rc = tty_register_driver(driver);
 	if (rc) {
 		put_tty_driver(driver);
 		tty_port_destroy(&sclp_port);
 		return rc;
 	}
 	sclp_tty_driver = driver;
 	return 0;
 }
 device_initcall(sclp_tty_init);
	// SPDX-License-Identifier: GPL-2.0
	/*
	* SCLP line mode terminal driver.
	*
	* S390 version
	* Copyright IBM Corp. 1999
	* Author(s): Martin Peschke <mpeschke@de.ibm.com>
	* Martin Schwidefsky <schwidefsky@de.ibm.com>
	*/

	#include <linux/kmod.h>
	#include <linux/tty.h>
	#include <linux/tty_driver.h>
	#include <linux/tty_flip.h>
	#include <linux/err.h>
	#include <linux/init.h>
	#include <linux/interrupt.h>
	#include <linux/gfp.h>
	#include <linux/uaccess.h>

	#include "ctrlchar.h"
	#include "sclp.h"
	#include "sclp_rw.h"
	#include "sclp_tty.h"

	/*
	* size of a buffer that collects single characters coming in
	* via sclp_tty_put_char()
	*/
	#define SCLP_TTY_BUF_SIZE 512

	/*
	* There is exactly one SCLP terminal, so we can keep things simple
	* and allocate all variables statically.
	*/

	/* Lock to guard over changes to global variables. */
	static spinlock_t sclp_tty_lock;
	/* List of free pages that can be used for console output buffering. */
	static struct list_head sclp_tty_pages;
	/* List of full struct sclp_buffer structures ready for output. */
	static struct list_head sclp_tty_outqueue;
	/* Counter how many buffers are emitted. */
	static int sclp_tty_buffer_count;
	/* Pointer to current console buffer. */
	static struct sclp_buffer *sclp_ttybuf;
	/* Timer for delayed output of console messages. */
	static struct timer_list sclp_tty_timer;

	static struct tty_port sclp_port;
	static unsigned char sclp_tty_chars[SCLP_TTY_BUF_SIZE];
	static unsigned short int sclp_tty_chars_count;

	struct tty_driver *sclp_tty_driver;

	static int sclp_tty_tolower;
	static int sclp_tty_columns = 80;

	#define SPACES_PER_TAB 8
	#define CASE_DELIMITER 0x6c /* to separate upper and lower case (% in EBCDIC) */

	/* This routine is called whenever we try to open a SCLP terminal. */
	static int
	sclp_tty_open(struct tty_struct tty, struct file filp)
	{
	tty_port_tty_set(&sclp_port, tty);
	tty->driver_data = NULL;
	return 0;
	}

	/* This routine is called when the SCLP terminal is closed. */
	static void
	sclp_tty_close(struct tty_struct tty, struct file filp)
	{
	if (tty->count > 1)
	return;
	tty_port_tty_set(&sclp_port, NULL);
	}

	/*
	* This routine returns the numbers of characters the tty driver
	* will accept for queuing to be written. This number is subject
	* to change as output buffers get emptied, or if the output flow
	* control is acted. This is not an exact number because not every
	* character needs the same space in the sccb. The worst case is
	* a string of newlines. Every newline creates a new message which
	* needs 82 bytes.
	*/
	static int
	sclp_tty_write_room (struct tty_struct *tty)
	{
	unsigned long flags;
	struct list_head *l;
	int count;

	spin_lock_irqsave(&sclp_tty_lock, flags);
	count = 0;
	if (sclp_ttybuf != NULL)
	count = sclp_buffer_space(sclp_ttybuf) / sizeof(struct msg_buf);
	list_for_each(l, &sclp_tty_pages)
	count += NR_EMPTY_MSG_PER_SCCB;
	spin_unlock_irqrestore(&sclp_tty_lock, flags);
	return count;
	}

	static void
	sclp_ttybuf_callback(struct sclp_buffer *buffer, int rc)
	{
	unsigned long flags;
	void *page;

	do {
	page = sclp_unmake_buffer(buffer);
	spin_lock_irqsave(&sclp_tty_lock, flags);
	/* Remove buffer from outqueue */
	list_del(&buffer->list);
	sclp_tty_buffer_count--;
	list_add_tail((struct list_head *) page, &sclp_tty_pages);
	/* Check if there is a pending buffer on the out queue. */
	buffer = NULL;
	if (!list_empty(&sclp_tty_outqueue))
	buffer = list_entry(sclp_tty_outqueue.next,
	struct sclp_buffer, list);
	spin_unlock_irqrestore(&sclp_tty_lock, flags);
	} while (buffer && sclp_emit_buffer(buffer, sclp_ttybuf_callback));

	tty_port_tty_wakeup(&sclp_port);
	}

	static inline void
	__sclp_ttybuf_emit(struct sclp_buffer *buffer)
	{
	unsigned long flags;
	int count;
	int rc;

	spin_lock_irqsave(&sclp_tty_lock, flags);
	list_add_tail(&buffer->list, &sclp_tty_outqueue);
	count = sclp_tty_buffer_count++;
	spin_unlock_irqrestore(&sclp_tty_lock, flags);
	if (count)
	return;
	rc = sclp_emit_buffer(buffer, sclp_ttybuf_callback);
	if (rc)
	sclp_ttybuf_callback(buffer, rc);
	}

	/*
	* When this routine is called from the timer then we flush the
	* temporary write buffer.
	*/
	static void
	sclp_tty_timeout(struct timer_list *unused)
	{
	unsigned long flags;
	struct sclp_buffer *buf;

	spin_lock_irqsave(&sclp_tty_lock, flags);
	buf = sclp_ttybuf;
	sclp_ttybuf = NULL;
	spin_unlock_irqrestore(&sclp_tty_lock, flags);

	if (buf != NULL) {
	__sclp_ttybuf_emit(buf);
	}
	}

	/*
	* Write a string to the sclp tty.
	*/
	static int sclp_tty_write_string(const unsigned char *str, int count, int may_fail)
	{
	unsigned long flags;
	void *page;
	int written;
	int overall_written;
	struct sclp_buffer *buf;

	if (count <= 0)
	return 0;
	overall_written = 0;
	spin_lock_irqsave(&sclp_tty_lock, flags);
	do {
	/* Create a sclp output buffer if none exists yet */
	if (sclp_ttybuf == NULL) {
	while (list_empty(&sclp_tty_pages)) {
	spin_unlock_irqrestore(&sclp_tty_lock, flags);
	if (may_fail)
	goto out;
	else
	sclp_sync_wait();
	spin_lock_irqsave(&sclp_tty_lock, flags);
	}
	page = sclp_tty_pages.next;
	list_del((struct list_head *) page);
	sclp_ttybuf = sclp_make_buffer(page, sclp_tty_columns,
	SPACES_PER_TAB);
	}
	/* try to write the string to the current output buffer */
	written = sclp_write(sclp_ttybuf, str, count);
	overall_written += written;
	if (written == count)
	break;
	/*
	* Not all characters could be written to the current
	* output buffer. Emit the buffer, create a new buffer
	* and then output the rest of the string.
	*/
	buf = sclp_ttybuf;
	sclp_ttybuf = NULL;
	spin_unlock_irqrestore(&sclp_tty_lock, flags);
	__sclp_ttybuf_emit(buf);
	spin_lock_irqsave(&sclp_tty_lock, flags);
	str += written;
	count -= written;
	} while (count > 0);
	/* Setup timer to output current console buffer after 1/10 second */
	if (sclp_ttybuf && sclp_chars_in_buffer(sclp_ttybuf) &&
	!timer_pending(&sclp_tty_timer)) {
	mod_timer(&sclp_tty_timer, jiffies + HZ / 10);
	}
	spin_unlock_irqrestore(&sclp_tty_lock, flags);
	out:
	return overall_written;
	}

	/*
	* This routine is called by the kernel to write a series of characters to the
	* tty device. The characters may come from user space or kernel space. This
	* routine will return the number of characters actually accepted for writing.
	*/
	static int
	sclp_tty_write(struct tty_struct tty, const unsigned char buf, int count)
	{
	if (sclp_tty_chars_count > 0) {
	sclp_tty_write_string(sclp_tty_chars, sclp_tty_chars_count, 0);
	sclp_tty_chars_count = 0;
	}
	return sclp_tty_write_string(buf, count, 1);
	}

	/*
	* This routine is called by the kernel to write a single character to the tty
	* device. If the kernel uses this routine, it must call the flush_chars()
	* routine (if defined) when it is done stuffing characters into the driver.
	*
	* Characters provided to sclp_tty_put_char() are buffered by the SCLP driver.
	* If the given character is a '\n' the contents of the SCLP write buffer
	* - including previous characters from sclp_tty_put_char() and strings from
	* sclp_write() without final '\n' - will be written.
	*/
	static int
	sclp_tty_put_char(struct tty_struct *tty, unsigned char ch)
	{
	sclp_tty_chars[sclp_tty_chars_count++] = ch;
	if (ch == '\n' \|\| sclp_tty_chars_count >= SCLP_TTY_BUF_SIZE) {
	sclp_tty_write_string(sclp_tty_chars, sclp_tty_chars_count, 0);
	sclp_tty_chars_count = 0;
	}
	return 1;
	}

	/*
	* This routine is called by the kernel after it has written a series of
	* characters to the tty device using put_char().
	*/
	static void
	sclp_tty_flush_chars(struct tty_struct *tty)
	{
	if (sclp_tty_chars_count > 0) {
	sclp_tty_write_string(sclp_tty_chars, sclp_tty_chars_count, 0);
	sclp_tty_chars_count = 0;
	}
	}

	/*
	* This routine returns the number of characters in the write buffer of the
	* SCLP driver. The provided number includes all characters that are stored
	* in the SCCB (will be written next time the SCLP is not busy) as well as
	* characters in the write buffer (will not be written as long as there is a
	* final line feed missing).
	*/
	static int
	sclp_tty_chars_in_buffer(struct tty_struct *tty)
	{
	unsigned long flags;
	struct list_head *l;
	struct sclp_buffer *t;
	int count;

	spin_lock_irqsave(&sclp_tty_lock, flags);
	count = 0;
	if (sclp_ttybuf != NULL)
	count = sclp_chars_in_buffer(sclp_ttybuf);
	list_for_each(l, &sclp_tty_outqueue) {
	t = list_entry(l, struct sclp_buffer, list);
	count += sclp_chars_in_buffer(t);
	}
	spin_unlock_irqrestore(&sclp_tty_lock, flags);
	return count;
	}

	/*
	* removes all content from buffers of low level driver
	*/
	static void
	sclp_tty_flush_buffer(struct tty_struct *tty)
	{
	if (sclp_tty_chars_count > 0) {
	sclp_tty_write_string(sclp_tty_chars, sclp_tty_chars_count, 0);
	sclp_tty_chars_count = 0;
	}
	}

	/*
	* push input to tty
	*/
	static void
	sclp_tty_input(unsigned char* buf, unsigned int count)
	{
	struct tty_struct *tty = tty_port_tty_get(&sclp_port);
	unsigned int cchar;

	/*
	* If this tty driver is currently closed
	* then throw the received input away.
	*/
	if (tty == NULL)
	return;
	cchar = ctrlchar_handle(buf, count, tty);
	switch (cchar & CTRLCHAR_MASK) {
	case CTRLCHAR_SYSRQ:
	break;
	case CTRLCHAR_CTRL:
	tty_insert_flip_char(&sclp_port, cchar, TTY_NORMAL);
	tty_flip_buffer_push(&sclp_port);
	break;
	case CTRLCHAR_NONE:
	/* send (normal) input to line discipline */
	if (count < 2 \|\|
	(strncmp((const char *) buf + count - 2, "^n", 2) &&
	strncmp((const char *) buf + count - 2, "\252n", 2))) {
	/* add the auto \n */
	tty_insert_flip_string(&sclp_port, buf, count);
	tty_insert_flip_char(&sclp_port, '\n', TTY_NORMAL);
	} else
	tty_insert_flip_string(&sclp_port, buf, count - 2);
	tty_flip_buffer_push(&sclp_port);
	break;
	}
	tty_kref_put(tty);
	}

	/*
	* get a EBCDIC string in upper/lower case,
	* find out characters in lower/upper case separated by a special character,
	* modifiy original string,
	* returns length of resulting string
	*/
	static int sclp_switch_cases(unsigned char *buf, int count)
	{
	unsigned char ip, op;
	int toggle;

	/* initially changing case is off */
	toggle = 0;
	ip = op = buf;
	while (count-- > 0) {
	/* compare with special character */
	if (*ip == CASE_DELIMITER) {
	/* followed by another special character? */
	if (count && ip[1] == CASE_DELIMITER) {
	/*
	* ... then put a single copy of the special
	* character to the output string
	*/
	op++ = ip++;
	count--;
	} else
	/*
	* ... special character follower by a normal
	* character toggles the case change behaviour
	*/
	toggle = ~toggle;
	/* skip special character */
	ip++;
	} else
	/* not the special character */
	if (toggle)
	/* but case switching is on */
	if (sclp_tty_tolower)
	/* switch to uppercase */
	op++ = _ebc_toupper[(int) ip++];
	else
	/* switch to lowercase */
	op++ = _ebc_tolower[(int) ip++];
	else
	/* no case switching, copy the character */
	op++ = ip++;
	}
	/* return length of reformatted string. */
	return op - buf;
	}

	static void sclp_get_input(struct gds_subvector *sv)
	{
	unsigned char *str;
	int count;

	str = (unsigned char *) (sv + 1);
	count = sv->length - sizeof(*sv);
	if (sclp_tty_tolower)
	EBC_TOLOWER(str, count);
	count = sclp_switch_cases(str, count);
	/* convert EBCDIC to ASCII (modify original input in SCCB) */
	sclp_ebcasc_str(str, count);

	/* transfer input to high level driver */
	sclp_tty_input(str, count);
	}

	static inline void sclp_eval_selfdeftextmsg(struct gds_subvector *sv)
	{
	void *end;

	end = (void *) sv + sv->length;
	for (sv = sv + 1; (void ) sv < end; sv = (void ) sv + sv->length)
	if (sv->key == 0x30)
	sclp_get_input(sv);
	}

	static inline void sclp_eval_textcmd(struct gds_vector *v)
	{
	struct gds_subvector *sv;
	void *end;

	end = (void *) v + v->length;
	for (sv = (struct gds_subvector *) (v + 1);
	(void ) sv < end; sv = (void ) sv + sv->length)
	if (sv->key == GDS_KEY_SELFDEFTEXTMSG)
	sclp_eval_selfdeftextmsg(sv);

	}

	static inline void sclp_eval_cpmsu(struct gds_vector *v)
	{
	void *end;

	end = (void *) v + v->length;
	for (v = v + 1; (void ) v < end; v = (void ) v + v->length)
	if (v->gds_id == GDS_ID_TEXTCMD)
	sclp_eval_textcmd(v);
	}


	static inline void sclp_eval_mdsmu(struct gds_vector *v)
	{
	v = sclp_find_gds_vector(v + 1, (void *) v + v->length, GDS_ID_CPMSU);
	if (v)
	sclp_eval_cpmsu(v);
	}

	static void sclp_tty_receiver(struct evbuf_header *evbuf)
	{
	struct gds_vector *v;

	v = sclp_find_gds_vector(evbuf + 1, (void *) evbuf + evbuf->length,
	GDS_ID_MDSMU);
	if (v)
	sclp_eval_mdsmu(v);
	}

	static void
	sclp_tty_state_change(struct sclp_register *reg)
	{
	}

	static struct sclp_register sclp_input_event =
	{
	.receive_mask = EVTYP_OPCMD_MASK \| EVTYP_PMSGCMD_MASK,
	.state_change_fn = sclp_tty_state_change,
	.receiver_fn = sclp_tty_receiver
	};

	static const struct tty_operations sclp_ops = {
	.open = sclp_tty_open,
	.close = sclp_tty_close,
	.write = sclp_tty_write,
	.put_char = sclp_tty_put_char,
	.flush_chars = sclp_tty_flush_chars,
	.write_room = sclp_tty_write_room,
	.chars_in_buffer = sclp_tty_chars_in_buffer,
	.flush_buffer = sclp_tty_flush_buffer,
	};

	static int __init
	sclp_tty_init(void)
	{
	struct tty_driver *driver;
	void *page;
	int i;
	int rc;

	/* z/VM multiplexes the line mode output on the 32xx screen */
	if (MACHINE_IS_VM && !CONSOLE_IS_SCLP)
	return 0;
	if (!sclp.has_linemode)
	return 0;
	driver = alloc_tty_driver(1);
	if (!driver)
	return -ENOMEM;

	rc = sclp_rw_init();
	if (rc) {
	put_tty_driver(driver);
	return rc;
	}
	/* Allocate pages for output buffering */
	INIT_LIST_HEAD(&sclp_tty_pages);
	for (i = 0; i < MAX_KMEM_PAGES; i++) {
	page = (void *) get_zeroed_page(GFP_KERNEL \| GFP_DMA);
	if (page == NULL) {
	put_tty_driver(driver);
	return -ENOMEM;
	}
	list_add_tail((struct list_head *) page, &sclp_tty_pages);
	}
	INIT_LIST_HEAD(&sclp_tty_outqueue);
	spin_lock_init(&sclp_tty_lock);
	timer_setup(&sclp_tty_timer, sclp_tty_timeout, 0);
	sclp_ttybuf = NULL;
	sclp_tty_buffer_count = 0;
	if (MACHINE_IS_VM) {
	/*
	* save 4 characters for the CPU number
	* written at start of each line by VM/CP
	*/
	sclp_tty_columns = 76;
	/* case input lines to lowercase */
	sclp_tty_tolower = 1;
	}
	sclp_tty_chars_count = 0;

	rc = sclp_register(&sclp_input_event);
	if (rc) {
	put_tty_driver(driver);
	return rc;
	}

	tty_port_init(&sclp_port);

	driver->driver_name = "sclp_line";
	driver->name = "sclp_line";
	driver->major = TTY_MAJOR;
	driver->minor_start = 64;
	driver->type = TTY_DRIVER_TYPE_SYSTEM;
	driver->subtype = SYSTEM_TYPE_TTY;
	driver->init_termios = tty_std_termios;
	driver->init_termios.c_iflag = IGNBRK \| IGNPAR;
	driver->init_termios.c_oflag = ONLCR;
	driver->init_termios.c_lflag = ISIG \| ECHO;
	driver->flags = TTY_DRIVER_REAL_RAW;
	tty_set_operations(driver, &sclp_ops);
	tty_port_link_device(&sclp_port, driver, 0);
	rc = tty_register_driver(driver);
	if (rc) {
	put_tty_driver(driver);
	tty_port_destroy(&sclp_port);
	return rc;
	}
	sclp_tty_driver = driver;
	return 0;
	}
	device_initcall(sclp_tty_init);