1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  4 */
  5
  6#include <linux/types.h>
  7#include <linux/kernel.h>
  8#include <linux/termios.h>
  9#include <linux/tty.h>
 10#include <linux/export.h>
 11#include "tty.h"
 12
 13
 14/*
 15 * Routine which returns the baud rate of the tty
 16 *
 17 * Note that the baud_table needs to be kept in sync with the
 18 * include/asm/termbits.h file.
 19 */
 20static const speed_t baud_table[] = {
 21	0, 50, 75, 110, 134, 150, 200, 300, 600, 1200, 1800, 2400,
 22	4800, 9600, 19200, 38400, 57600, 115200, 230400, 460800,
 23#ifdef __sparc__
 24	76800, 153600, 307200, 614400, 921600, 500000, 576000,
 25	1000000, 1152000, 1500000, 2000000
 26#else
 27	500000, 576000, 921600, 1000000, 1152000, 1500000, 2000000,
 28	2500000, 3000000, 3500000, 4000000
 29#endif
 30};
 31
 32static const tcflag_t baud_bits[] = {
 33	B0, B50, B75, B110, B134, B150, B200, B300, B600, B1200, B1800, B2400,
 34	B4800, B9600, B19200, B38400, B57600, B115200, B230400, B460800,
 35#ifdef __sparc__
 36	B76800, B153600, B307200, B614400, B921600, B500000, B576000,
 37	B1000000, B1152000, B1500000, B2000000
 38#else
 39	B500000, B576000, B921600, B1000000, B1152000, B1500000, B2000000,
 40	B2500000, B3000000, B3500000, B4000000
 41#endif
 42};
 43
 44static int n_baud_table = ARRAY_SIZE(baud_table);
 45
 46/**
 47 *	tty_termios_baud_rate
 48 *	@termios: termios structure
 49 *
 50 *	Convert termios baud rate data into a speed. This should be called
 51 *	with the termios lock held if this termios is a terminal termios
 52 *	structure. Device drivers can call this function but should use
 53 *	->c_[io]speed directly as they are updated.
 54 *
 55 *	Locking: none
 56 */
 57
 58speed_t tty_termios_baud_rate(const struct ktermios *termios)
 59{
 60	unsigned int cbaud;
 61
 62	cbaud = termios->c_cflag & CBAUD;
 63
 64	/* Magic token for arbitrary speed via c_ispeed/c_ospeed */
 65	if (cbaud == BOTHER)
 66		return termios->c_ospeed;
 67
 68	if (cbaud & CBAUDEX) {
 69		cbaud &= ~CBAUDEX;
 70		cbaud += 15;
 71	}
 72	return cbaud >= n_baud_table ? 0 : baud_table[cbaud];
 73}
 74EXPORT_SYMBOL(tty_termios_baud_rate);
 75
 76/**
 77 *	tty_termios_input_baud_rate
 78 *	@termios: termios structure
 79 *
 80 *	Convert termios baud rate data into a speed. This should be called
 81 *	with the termios lock held if this termios is a terminal termios
 82 *	structure. Device drivers can call this function but should use
 83 *	->c_[io]speed directly as they are updated.
 84 *
 85 *	Locking: none
 86 */
 87
 88speed_t tty_termios_input_baud_rate(const struct ktermios *termios)
 89{
 90	unsigned int cbaud = (termios->c_cflag >> IBSHIFT) & CBAUD;
 91
 92	if (cbaud == B0)
 93		return tty_termios_baud_rate(termios);
 94
 95	/* Magic token for arbitrary speed via c_ispeed */
 96	if (cbaud == BOTHER)
 97		return termios->c_ispeed;
 98
 99	if (cbaud & CBAUDEX) {
100		cbaud &= ~CBAUDEX;
101		cbaud += 15;
102	}
103	return cbaud >= n_baud_table ? 0 : baud_table[cbaud];
104}
105EXPORT_SYMBOL(tty_termios_input_baud_rate);
106
107/**
108 *	tty_termios_encode_baud_rate
109 *	@termios: ktermios structure holding user requested state
110 *	@ibaud: input speed
111 *	@obaud: output speed
112 *
113 *	Encode the speeds set into the passed termios structure. This is
114 *	used as a library helper for drivers so that they can report back
115 *	the actual speed selected when it differs from the speed requested
116 *
117 *	For maximal back compatibility with legacy SYS5/POSIX *nix behaviour
118 *	we need to carefully set the bits when the user does not get the
119 *	desired speed. We allow small margins and preserve as much of possible
120 *	of the input intent to keep compatibility.
121 *
122 *	Locking: Caller should hold termios lock. This is already held
123 *	when calling this function from the driver termios handler.
124 *
125 *	The ifdefs deal with platforms whose owners have yet to update them
126 *	and will all go away once this is done.
127 */
128
129void tty_termios_encode_baud_rate(struct ktermios *termios,
130				  speed_t ibaud, speed_t obaud)
131{
132	int i = 0;
133	int ifound = -1, ofound = -1;
134	int iclose = ibaud/50, oclose = obaud/50;
135	int ibinput = 0;
136
137	if (obaud == 0)			/* CD dropped */
138		ibaud = 0;		/* Clear ibaud to be sure */
139
140	termios->c_ispeed = ibaud;
141	termios->c_ospeed = obaud;
142
143	if (((termios->c_cflag >> IBSHIFT) & CBAUD) != B0)
144		ibinput = 1;	/* An input speed was specified */
145
146	/* If the user asked for a precise weird speed give a precise weird
147	 * answer. If they asked for a Bfoo speed they may have problems
148	 * digesting non-exact replies so fuzz a bit.
149	 */
150
151	if ((termios->c_cflag & CBAUD) == BOTHER) {
152		oclose = 0;
153		if (!ibinput)
154			iclose = 0;
155	}
156	if (((termios->c_cflag >> IBSHIFT) & CBAUD) == BOTHER)
157		iclose = 0;
158
159	termios->c_cflag &= ~CBAUD;
160	termios->c_cflag &= ~(CBAUD << IBSHIFT);
161
162	/*
163	 *	Our goal is to find a close match to the standard baud rate
164	 *	returned. Walk the baud rate table and if we get a very close
165	 *	match then report back the speed as a POSIX Bxxxx value by
166	 *	preference
167	 */
168
169	do {
170		if (obaud - oclose <= baud_table[i] &&
171		    obaud + oclose >= baud_table[i]) {
172			termios->c_cflag |= baud_bits[i];
173			ofound = i;
174		}
175		if (ibaud - iclose <= baud_table[i] &&
176		    ibaud + iclose >= baud_table[i]) {
177			/* For the case input == output don't set IBAUD bits
178			 * if the user didn't do so.
179			 */
180			if (ofound == i && !ibinput) {
181				ifound  = i;
182			} else {
183				ifound = i;
184				termios->c_cflag |= (baud_bits[i] << IBSHIFT);
185			}
186		}
187	} while (++i < n_baud_table);
188
189	/* If we found no match then use BOTHER. */
190	if (ofound == -1)
191		termios->c_cflag |= BOTHER;
192	/* Set exact input bits only if the input and output differ or the
193	 * user already did.
194	 */
195	if (ifound == -1 && (ibaud != obaud || ibinput))
196		termios->c_cflag |= (BOTHER << IBSHIFT);
197}
198EXPORT_SYMBOL_GPL(tty_termios_encode_baud_rate);
199
200/**
201 *	tty_encode_baud_rate		-	set baud rate of the tty
202 *	@tty:   terminal device
203 *	@ibaud: input baud rate
204 *	@obaud: output baud rate
205 *
206 *	Update the current termios data for the tty with the new speed
207 *	settings. The caller must hold the termios_rwsem for the tty in
208 *	question.
209 */
210
211void tty_encode_baud_rate(struct tty_struct *tty, speed_t ibaud, speed_t obaud)
212{
213	tty_termios_encode_baud_rate(&tty->termios, ibaud, obaud);
214}
215EXPORT_SYMBOL_GPL(tty_encode_baud_rate);