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
  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);