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.genoud@xxxxxxxxx>
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;
--
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