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
 12
 13/*
 14 * Routine which returns the baud rate of the tty
 15 *
 16 * Note that the baud_table needs to be kept in sync with the
 17 * include/asm/termbits.h file.
 18 */
 19static const speed_t baud_table[] = {
 20	0, 50, 75, 110, 134, 150, 200, 300, 600, 1200, 1800, 2400,
 21	4800, 9600, 19200, 38400, 57600, 115200, 230400, 460800,
 22#ifdef __sparc__
 23	76800, 153600, 307200, 614400, 921600, 500000, 576000,
 24	1000000, 1152000, 1500000, 2000000
 25#else
 26	500000, 576000, 921600, 1000000, 1152000, 1500000, 2000000,
 27	2500000, 3000000, 3500000, 4000000
 28#endif
 29};
 30
 31static const tcflag_t baud_bits[] = {
 32	B0, B50, B75, B110, B134, B150, B200, B300, B600, B1200, B1800, B2400,
 33	B4800, B9600, B19200, B38400, B57600, B115200, B230400, B460800,
 34#ifdef __sparc__
 35	B76800, B153600, B307200, B614400, B921600, B500000, B576000,
 36	B1000000, B1152000, B1500000, B2000000
 37#else
 38	B500000, B576000, B921600, B1000000, B1152000, B1500000, B2000000,
 39	B2500000, B3000000, B3500000, B4000000
 40#endif
 41};
 42
 43static int n_baud_table = ARRAY_SIZE(baud_table);
 44
 45/**
 46 *	tty_termios_baud_rate
 47 *	@termios: termios structure
 48 *
 49 *	Convert termios baud rate data into a speed. This should be called
 50 *	with the termios lock held if this termios is a terminal termios
 51 *	structure. May change the termios data. Device drivers can call this
 52 *	function but should use ->c_[io]speed directly as they are updated.
 53 *
 54 *	Locking: none
 55 */
 56
 57speed_t tty_termios_baud_rate(struct ktermios *termios)
 58{
 59	unsigned int cbaud;
 60
 61	cbaud = termios->c_cflag & CBAUD;
 62
 63#ifdef BOTHER
 64	/* Magic token for arbitrary speed via c_ispeed/c_ospeed */
 65	if (cbaud == BOTHER)
 66		return termios->c_ospeed;
 67#endif
 68	if (cbaud & CBAUDEX) {
 69		cbaud &= ~CBAUDEX;
 70
 71		if (cbaud < 1 || cbaud + 15 > n_baud_table)
 72			termios->c_cflag &= ~CBAUDEX;
 73		else
 74			cbaud += 15;
 75	}
 76	return cbaud >= n_baud_table ? 0 : baud_table[cbaud];
 77}
 78EXPORT_SYMBOL(tty_termios_baud_rate);
 79
 80/**
 81 *	tty_termios_input_baud_rate
 82 *	@termios: termios structure
 83 *
 84 *	Convert termios baud rate data into a speed. This should be called
 85 *	with the termios lock held if this termios is a terminal termios
 86 *	structure. May change the termios data. Device drivers can call this
 87 *	function but should use ->c_[io]speed directly as they are updated.
 88 *
 89 *	Locking: none
 90 */
 91
 92speed_t tty_termios_input_baud_rate(struct ktermios *termios)
 93{
 94#ifdef IBSHIFT
 95	unsigned int cbaud = (termios->c_cflag >> IBSHIFT) & CBAUD;
 96
 97	if (cbaud == B0)
 98		return tty_termios_baud_rate(termios);
 99#ifdef BOTHER
100	/* Magic token for arbitrary speed via c_ispeed*/
101	if (cbaud == BOTHER)
102		return termios->c_ispeed;
103#endif
104	if (cbaud & CBAUDEX) {
105		cbaud &= ~CBAUDEX;
106
107		if (cbaud < 1 || cbaud + 15 > n_baud_table)
108			termios->c_cflag &= ~(CBAUDEX << IBSHIFT);
109		else
110			cbaud += 15;
111	}
112	return cbaud >= n_baud_table ? 0 : baud_table[cbaud];
113#else	/* IBSHIFT */
114	return tty_termios_baud_rate(termios);
115#endif	/* IBSHIFT */
116}
117EXPORT_SYMBOL(tty_termios_input_baud_rate);
118
119/**
120 *	tty_termios_encode_baud_rate
121 *	@termios: ktermios structure holding user requested state
122 *	@ispeed: input speed
123 *	@ospeed: output speed
124 *
125 *	Encode the speeds set into the passed termios structure. This is
126 *	used as a library helper for drivers so that they can report back
127 *	the actual speed selected when it differs from the speed requested
128 *
129 *	For maximal back compatibility with legacy SYS5/POSIX *nix behaviour
130 *	we need to carefully set the bits when the user does not get the
131 *	desired speed. We allow small margins and preserve as much of possible
132 *	of the input intent to keep compatibility.
133 *
134 *	Locking: Caller should hold termios lock. This is already held
135 *	when calling this function from the driver termios handler.
136 *
137 *	The ifdefs deal with platforms whose owners have yet to update them
138 *	and will all go away once this is done.
139 */
140
141void tty_termios_encode_baud_rate(struct ktermios *termios,
142				  speed_t ibaud, speed_t obaud)
143{
144	int i = 0;
145	int ifound = -1, ofound = -1;
146	int iclose = ibaud/50, oclose = obaud/50;
147	int ibinput = 0;
148
149	if (obaud == 0)			/* CD dropped 		  */
150		ibaud = 0;		/* Clear ibaud to be sure */
151
152	termios->c_ispeed = ibaud;
153	termios->c_ospeed = obaud;
154
155#ifdef IBSHIFT
156	if ((termios->c_cflag >> IBSHIFT) & CBAUD)
157		ibinput = 1;	/* An input speed was specified */
158#endif
159#ifdef BOTHER
160	/* If the user asked for a precise weird speed give a precise weird
161	   answer. If they asked for a Bfoo speed they may have problems
162	   digesting non-exact replies so fuzz a bit */
163
164	if ((termios->c_cflag & CBAUD) == BOTHER) {
165		oclose = 0;
166		if (!ibinput)
167			iclose = 0;
168	}
169	if (((termios->c_cflag >> IBSHIFT) & CBAUD) == BOTHER)
170		iclose = 0;
171#endif
172	termios->c_cflag &= ~CBAUD;
173#ifdef IBSHIFT
174	termios->c_cflag &= ~(CBAUD << IBSHIFT);
175#endif
176
177	/*
178	 *	Our goal is to find a close match to the standard baud rate
179	 *	returned. Walk the baud rate table and if we get a very close
180	 *	match then report back the speed as a POSIX Bxxxx value by
181	 *	preference
182	 */
183
184	do {
185		if (obaud - oclose <= baud_table[i] &&
186		    obaud + oclose >= baud_table[i]) {
187			termios->c_cflag |= baud_bits[i];
188			ofound = i;
189		}
190		if (ibaud - iclose <= baud_table[i] &&
191		    ibaud + iclose >= baud_table[i]) {
192			/* For the case input == output don't set IBAUD bits
193			   if the user didn't do so */
194			if (ofound == i && !ibinput)
195				ifound  = i;
196#ifdef IBSHIFT
197			else {
198				ifound = i;
199				termios->c_cflag |= (baud_bits[i] << IBSHIFT);
200			}
201#endif
202		}
203	} while (++i < n_baud_table);
204
205	/*
206	 *	If we found no match then use BOTHER if provided or warn
207	 *	the user their platform maintainer needs to wake up if not.
208	 */
209#ifdef BOTHER
210	if (ofound == -1)
211		termios->c_cflag |= BOTHER;
212	/* Set exact input bits only if the input and output differ or the
213	   user already did */
214	if (ifound == -1 && (ibaud != obaud || ibinput))
215		termios->c_cflag |= (BOTHER << IBSHIFT);
216#else
217	if (ifound == -1 || ofound == -1)
218		pr_warn_once("tty: Unable to return correct speed data as your architecture needs updating.\n");
219#endif
220}
221EXPORT_SYMBOL_GPL(tty_termios_encode_baud_rate);
222
223/**
224 *	tty_encode_baud_rate		-	set baud rate of the tty
225 *	@ibaud: input baud rate
226 *	@obad: output baud rate
227 *
228 *	Update the current termios data for the tty with the new speed
229 *	settings. The caller must hold the termios_rwsem for the tty in
230 *	question.
231 */
232
233void tty_encode_baud_rate(struct tty_struct *tty, speed_t ibaud, speed_t obaud)
234{
235	tty_termios_encode_baud_rate(&tty->termios, ibaud, obaud);
236}
237EXPORT_SYMBOL_GPL(tty_encode_baud_rate);