drivers/tty/tty_baudrate.c

   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
  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
  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
 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
 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);