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Subject[PATCH 4.9 017/109] serial: 8250_fintek: Fix rs485 disablement on invalid ioctl()
4.9-stable review patch.  If anyone has any objections, please let me know.


From: Lukas Wunner <>

[ Upstream commit 3236a965486ba0c6043cf2c7b51943d8b382ae29 ]

This driver's ->rs485_config callback checks if SER_RS485_RTS_ON_SEND
and SER_RS485_RTS_AFTER_SEND have the same value. If they do, it means
the user has passed in invalid data with the TIOCSRS485 ioctl()
since RTS must have a different polarity when sending and when not
sending. In this case, rs485 mode is not enabled (the RS485_URA bit
is not set in the RS485 Enable Register) and this is supposed to be
signaled back to the user by clearing the SER_RS485_ENABLED bit in
struct serial_rs485 ... except a missing tilde character is preventing
that from happening.

Fixes: 28e3fb6c4dce ("serial: Add support for Fintek F81216A LPC to 4 UART")
Cc: Ricardo Ribalda Delgado <>
Cc: "Ji-Ze Hong (Peter Hong)" <>
Signed-off-by: Lukas Wunner <>
Signed-off-by: Greg Kroah-Hartman <>
Signed-off-by: Sasha Levin <>
Signed-off-by: Greg Kroah-Hartman <>
drivers/tty/serial/8250/8250_fintek.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/tty/serial/8250/8250_fintek.c
+++ b/drivers/tty/serial/8250/8250_fintek.c
@@ -121,7 +121,7 @@ static int fintek_8250_rs485_config(stru

if ((!!(rs485->flags & SER_RS485_RTS_ON_SEND)) ==
(!!(rs485->flags & SER_RS485_RTS_AFTER_SEND)))
- rs485->flags &= SER_RS485_ENABLED;
+ rs485->flags &= ~SER_RS485_ENABLED;
config |= RS485_URA;

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