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tty: fix termios input-speed encoding when using BOTHER 

When the termios CIBAUD bits are left unset (i.e. B0), we use the same
output and input speed and should leave CIBAUD unchanged.

When the user requests a rate using BOTHER and c_ospeed which the driver
cannot set exactly, the driver can report back the actual baud rate
using tty_termios_encode_baud_rate(). If this rate is close enough to a
standard rate however, we could end up setting CIBAUD to a Bfoo value
despite the user having left it unset.

This in turn could lead to an unexpected input rate being set on
subsequent termios updates.

Fix this by using a zero tolerance value also for the input rate when
CIBAUD is clear so that the matching logic works as expected.

Fixes: 78137e3b34 ("[PATCH] tty: improve encode_baud_rate logic")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Johan Hovold 2018-07-15 15:39:34 +02:00 committed by Greg Kroah-Hartman
parent fada18c48d
commit 1cee38f036
1 changed files with 7 additions and 3 deletions
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10
drivers/tty/tty_baudrate.c
View File

@ -157,16 +157,20 @@ void tty_termios_encode_baud_rate(struct ktermios *termios,
termios->c_ospeed = obaud;
#ifdef BOTHER
if ((termios->c_cflag >> IBSHIFT) & CBAUD)
ibinput = 1; /* An input speed was specified */
/* If the user asked for a precise weird speed give a precise weird
answer. If they asked for a Bfoo speed they may have problems
digesting non-exact replies so fuzz a bit */
if ((termios->c_cflag & CBAUD) == BOTHER)
if ((termios->c_cflag & CBAUD) == BOTHER) {
oclose = 0;
if (!ibinput)
iclose = 0;
}
if (((termios->c_cflag >> IBSHIFT) & CBAUD) == BOTHER)
iclose = 0;
if ((termios->c_cflag >> IBSHIFT) & CBAUD)
ibinput = 1; /* An input speed was specified */
#endif
termios->c_cflag &= ~CBAUD;
#ifdef IBSHIFT