From 0ccad87012c6c2e7446e4dc0f0894cf182a5270a Mon Sep 17 00:00:00 2001 From: Haavard Skinnemoen Date: Tue, 16 Jun 2009 17:02:03 +0100 Subject: [PATCH] atmel_serial: fix hang in set_termios when crtscts is enabled After enabling hardware flow control, any subsequent termios call may hang waiting for the transmitter to drain. This appears to be caused by a busy-loop in set_termios() waiting for the transmitter to become empty, which may take a very long time (or hang indefinitely) if the device at the other end is blocking us. A quick look through the tty and serial_core code indicates that any necessary flushing (which is optional) has already been done at this point, so there's no need for the driver to flush the transmitter on its own. Fix it by removing the busy-loop altogether. Tested-by: Eirik Aanonsen Signed-off-by: Haavard Skinnemoen Signed-off-by: Andrew Morton Signed-off-by: Alan Cox Signed-off-by: Linus Torvalds --- drivers/serial/atmel_serial.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/drivers/serial/atmel_serial.c b/drivers/serial/atmel_serial.c index b3497d7e5354..338b15c0a548 100644 --- a/drivers/serial/atmel_serial.c +++ b/drivers/serial/atmel_serial.c @@ -1104,11 +1104,13 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios, /* update the per-port timeout */ uart_update_timeout(port, termios->c_cflag, baud); - /* save/disable interrupts and drain transmitter */ + /* + * save/disable interrupts. The tty layer will ensure that the + * transmitter is empty if requested by the caller, so there's + * no need to wait for it here. + */ imr = UART_GET_IMR(port); UART_PUT_IDR(port, -1); - while (!(UART_GET_CSR(port) & ATMEL_US_TXEMPTY)) - cpu_relax(); /* disable receiver and transmitter */ UART_PUT_CR(port, ATMEL_US_TXDIS | ATMEL_US_RXDIS); -- 2.39.2