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 <richard.gen...@gmail.com>
Fixes: 1cf6e8fc8341 ("tty/serial: at91: fix RTS line management when hardware
handshake is enabled")
---
drivers/tty/serial/atmel_serial.c | 24 ++++++++++++++----------
1 file changed, 14 insertions(+), 10 deletions(-)
diff --git a/drivers/tty/serial/atmel_serial.c
b/drivers/tty/serial/atmel_serial.c
index 14467d5e060b..f644d5dcf6d1 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -2131,19 +2131,23 @@ static void atmel_set_termios(struct uart_port *port,
struct ktermios *termios,
port->rs485.delay_rts_after_send);
mode |= ATMEL_US_USMODE_RS485;
} else if ((termios->c_cflag & CRTSCTS) &&
- !mctrl_gpio_use_rtscts(atmel_port->gpios)) {
+ !mctrl_gpio_use_rtscts(atmel_port->gpios) &&
+ (atmel_use_pdc_rx(port) || atmel_use_fifo(port))) {
/*
- * 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 {
- mode |= ATMEL_US_USMODE_HWHS;
- }
+ mode |= ATMEL_US_USMODE_HWHS;
} else {
- /* RS232 without hardware handshake or controlled by GPIOs */
+ /*
+ * Other cases are:
+ * - RS232 without hardware handshake
+ * - RS232 with hardware handshake and:
+ * - controller unable to handle CTS/RTS by itself
+ * - or CTS/RTS handled by GPIOs
+ */
mode |= ATMEL_US_USMODE_NORMAL;
}
