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  */
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,
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 
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,
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 
44 static 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 
tty_termios_baud_rate(const struct ktermios * termios)58 speed_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 }
74 EXPORT_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 
tty_termios_input_baud_rate(const struct ktermios * termios)88 speed_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 }
105 EXPORT_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 
tty_termios_encode_baud_rate(struct ktermios * termios,speed_t ibaud,speed_t obaud)129 void 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 }
198 EXPORT_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 
tty_encode_baud_rate(struct tty_struct * tty,speed_t ibaud,speed_t obaud)211 void 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 }
215 EXPORT_SYMBOL_GPL(tty_encode_baud_rate);
216