Commit 1cf6e8fc8341 ("tty/serial: at91: fix RTS line management when
hardware handshake is enabled") broke the hardware handshake on SAM9x5
platforms.On Atmel platforms, the USART can only handle the handware handshake (ATMEL_US_USMODE_HWHS) if FIFOs or PDC are used. Thus, ATMEL_US_USMODE_HWHS mode should only be used in this case. For SAM9x5, there's no FIFOs nor PDC for the USART, so the mode should be ATMEL_US_USMODE_NORMAL and the RTS pin should be controlled by the driver. NB: -stable is not Cced because it doesn't cleanly apply on 4.1+ Tested on SAM9G35-CM with and without DMA Signed-off-by: Richard Genoud <[email protected]> Fixes: 1cf6e8fc8341 ("tty/serial: at91: fix RTS line management when hardware handshake is enabled") --- drivers/tty/serial/atmel_serial.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c index e9b4fbf88c2d..32154e7231ce 100644 --- a/drivers/tty/serial/atmel_serial.c +++ b/drivers/tty/serial/atmel_serial.c @@ -2130,15 +2130,19 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios, } else if ((termios->c_cflag & CRTSCTS) && !mctrl_gpio_use_rtscts(atmel_port->gpios)) { /* - * RS232 with hardware handshake (RTS/CTS) - * handled by the controller. + * Automatic hardware handshake (RTS/CTS) only work with + * FIFOs or PDC. + * Meaning that on SAM9x5 the controller can't handle + * the hardware handshake (no FIFOs nor PDC on these platforms). */ - if (atmel_use_dma_rx(port) && !atmel_use_fifo(port)) { - dev_info(port->dev, "not enabling hardware flow control because DMA is used"); - termios->c_cflag &= ~CRTSCTS; - } else { + if (atmel_use_pdc_rx(port) || atmel_use_fifo(port)) mode |= ATMEL_US_USMODE_HWHS; - } + else + /* + * The hardware handshake won't be handle by the + * controller but by the driver. + */ + mode |= ATMEL_US_USMODE_NORMAL; } else { /* RS232 without hadware handshake or controlled by GPIOs */ mode |= ATMEL_US_USMODE_NORMAL;
