1 // SPDX-License-Identifier: GPL-2.0
3 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
6 #include <linux/types.h>
7 #include <linux/kernel.h>
8 #include <linux/termios.h>
10 #include <linux/export.h>
15 * Routine which returns the baud rate of the tty
17 * Note that the baud_table needs to be kept in sync with the
18 * include/asm/termbits.h file.
20 static 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,
24 76800, 153600, 307200, 614400, 921600, 500000, 576000,
25 1000000, 1152000, 1500000, 2000000
27 500000, 576000, 921600, 1000000, 1152000, 1500000, 2000000,
28 2500000, 3000000, 3500000, 4000000
32 static 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,
36 B76800, B153600, B307200, B614400, B921600, B500000, B576000,
37 B1000000, B1152000, B1500000, B2000000
39 B500000, B576000, B921600, B1000000, B1152000, B1500000, B2000000,
40 B2500000, B3000000, B3500000, B4000000
44 static int n_baud_table = ARRAY_SIZE(baud_table);
47 * tty_termios_baud_rate
48 * @termios: termios structure
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.
58 speed_t tty_termios_baud_rate(const struct ktermios *termios)
62 cbaud = termios->c_cflag & CBAUD;
64 /* Magic token for arbitrary speed via c_ispeed/c_ospeed */
66 return termios->c_ospeed;
68 if (cbaud & CBAUDEX) {
72 return cbaud >= n_baud_table ? 0 : baud_table[cbaud];
74 EXPORT_SYMBOL(tty_termios_baud_rate);
77 * tty_termios_input_baud_rate
78 * @termios: termios structure
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.
88 speed_t tty_termios_input_baud_rate(const struct ktermios *termios)
90 unsigned int cbaud = (termios->c_cflag >> IBSHIFT) & CBAUD;
93 return tty_termios_baud_rate(termios);
95 /* Magic token for arbitrary speed via c_ispeed */
97 return termios->c_ispeed;
99 if (cbaud & CBAUDEX) {
103 return cbaud >= n_baud_table ? 0 : baud_table[cbaud];
105 EXPORT_SYMBOL(tty_termios_input_baud_rate);
108 * tty_termios_encode_baud_rate
109 * @termios: ktermios structure holding user requested state
110 * @ibaud: input speed
111 * @obaud: output speed
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
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.
122 * Locking: Caller should hold termios lock. This is already held
123 * when calling this function from the driver termios handler.
125 * The ifdefs deal with platforms whose owners have yet to update them
126 * and will all go away once this is done.
129 void tty_termios_encode_baud_rate(struct ktermios *termios,
130 speed_t ibaud, speed_t obaud)
133 int ifound = -1, ofound = -1;
134 int iclose = ibaud/50, oclose = obaud/50;
137 if (obaud == 0) /* CD dropped */
138 ibaud = 0; /* Clear ibaud to be sure */
140 termios->c_ispeed = ibaud;
141 termios->c_ospeed = obaud;
143 if (((termios->c_cflag >> IBSHIFT) & CBAUD) != B0)
144 ibinput = 1; /* An input speed was specified */
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.
151 if ((termios->c_cflag & CBAUD) == BOTHER) {
156 if (((termios->c_cflag >> IBSHIFT) & CBAUD) == BOTHER)
159 termios->c_cflag &= ~CBAUD;
160 termios->c_cflag &= ~(CBAUD << IBSHIFT);
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
170 if (obaud - oclose <= baud_table[i] &&
171 obaud + oclose >= baud_table[i]) {
172 termios->c_cflag |= baud_bits[i];
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.
180 if (ofound == i && !ibinput) {
184 termios->c_cflag |= (baud_bits[i] << IBSHIFT);
187 } while (++i < n_baud_table);
189 /* If we found no match then use BOTHER. */
191 termios->c_cflag |= BOTHER;
192 /* Set exact input bits only if the input and output differ or the
195 if (ifound == -1 && (ibaud != obaud || ibinput))
196 termios->c_cflag |= (BOTHER << IBSHIFT);
198 EXPORT_SYMBOL_GPL(tty_termios_encode_baud_rate);
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
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
211 void tty_encode_baud_rate(struct tty_struct *tty, speed_t ibaud, speed_t obaud)
213 tty_termios_encode_baud_rate(&tty->termios, ibaud, obaud);
215 EXPORT_SYMBOL_GPL(tty_encode_baud_rate);