1 files changed, 30 insertions, 15 deletions

diff --git a/drivers/char/tty_ioctl.c b/drivers/char/tty_ioctl.c
index dee47f40c6a3..fd471cb3338f 100644
--- a/drivers/char/tty_ioctl.c
+++ b/drivers/char/tty_ioctl.c
@@ -225,7 +225,7 @@ EXPORT_SYMBOL(tty_termios_input_baud_rate);
 
 /**
  *      tty_termios_encode_baud_rate
- *      @termios: termios structure
+ *      @termios: ktermios structure holding user requested state
  *      @ispeed: input speed
  *      @ospeed: output speed
  *
@@ -233,7 +233,10 @@ EXPORT_SYMBOL(tty_termios_input_baud_rate);
  *      used as a library helper for drivers os that they can report back
  *      the actual speed selected when it differs from the speed requested
  *
- *      For now input and output speed must agree.
+ *      For maximal back compatibility with legacy SYS5/POSIX *nix behaviour
+ *      we need to carefully set the bits when the user does not get the
+ *      desired speed. We allow small margins and preserve as much of possible
+ *      of the input intent to keep compatiblity.
  *
  *      Locking: Caller should hold termios lock. This is already held
  *      when calling this function from the driver termios handler.
@@ -242,32 +245,44 @@ EXPORT_SYMBOL(tty_termios_input_baud_rate);
 void tty_termios_encode_baud_rate(struct ktermios *termios, speed_t ibaud, speed_t obaud)
 {
         int i = 0;
-        int ifound = 0, ofound = 0;
+        int ifound = -1, ofound = -1;
+        int iclose = ibaud/50, oclose = obaud/50;
+        int ibinput = 0;
 
         termios->c_ispeed = ibaud;
         termios->c_ospeed = obaud;
 
+        /* If the user asked for a precise weird speed give a precise weird
+           answer. If they asked for a Bfoo speed they many have problems
+           digesting non-exact replies so fuzz a bit */
+
+        if ((termios->c_cflag & CBAUD) == BOTHER)
+                oclose = 0;
+        if (((termios->c_cflag >> IBSHIFT) & CBAUD) == BOTHER)
+                iclose = 0;
+        if ((termios->c_cflag >> IBSHIFT) & CBAUD)
+                ibinput = 1;    /* An input speed was specified */
+
         termios->c_cflag &= ~CBAUD;
-        /* Identical speed means no input encoding (ie B0 << IBSHIFT)*/
-        if (termios->c_ispeed == termios->c_ospeed)
-                ifound = 1;
 
         do {
-                if (obaud == baud_table[i]) {
+                if (obaud - oclose >= baud_table[i] && obaud + oclose <= baud_table[i]) {
                         termios->c_cflag |= baud_bits[i];
-                        ofound = 1;
-                        /* So that if ibaud == obaud we don't set it */
-                        continue;
+                        ofound = i;
                 }
-                if (ibaud == baud_table[i]) {
-                        termios->c_cflag |= (baud_bits[i] << IBSHIFT);
-                        ifound = 1;
+                if (ibaud - iclose >= baud_table[i] && ibaud + iclose <= baud_table[i]) {
+                        /* For the case input == output don't set IBAUD bits if the user didn't do so */
+                        if (ofound != i || ibinput)
+                                termios->c_cflag |= (baud_bits[i] << IBSHIFT);
+                        ifound = i;
                 }
         }
         while(++i < n_baud_table);
-        if (!ofound)
+        if (ofound == -1)
                 termios->c_cflag |= BOTHER;
-        if (!ifound)
+        /* Set exact input bits only if the input and output differ or the
+           user already did */
+        if (ifound == -1 && (ibaud != obaud  || ibinput))
                 termios->c_cflag |= (BOTHER << IBSHIFT);
 }