xref: /openbmc/linux/drivers/tty/tty_baudrate.c (revision 78560d41)
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  */
19 static 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 
31 static 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 
43 static 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 
57 speed_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 }
78 EXPORT_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 
92 speed_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 }
117 EXPORT_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 
141 void 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 }
221 EXPORT_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 
233 void 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 }
237 EXPORT_SYMBOL_GPL(tty_encode_baud_rate);
238