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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);