[PATCH 3.16 040/328] tty: fix termios input-speed encoding when using BOTHER

Ben Hutchings
2018-12-09T22:12:08Z

From: Johan Hovold <johan@kernel.org>

commit 1cee38f0363a88db374e50b232ca17b9a4c12fa0 upstream.

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: 78137e3b34e1 ("[PATCH] tty: improve encode_baud_rate logic")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/tty/tty_ioctl.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -407,16 +407,20 @@ void tty_termios_encode_baud_rate(struct
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