On 12/09/2016 at 12:50:38 +0200, Richard Genoud wrote :

quoted

quoted

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;

You still need the case where HWHS is impossible and there are no gpio
configured. You need to inform userspace that the configuration was not
applied instead of silently ignoring the error.

Could you explain which case it is ?
The only one I can see is when there's no GPIO declared for RTS/CTS
AND, there's no pin muxed for RTS/CTS either.

Have you got another example in mind ?

Hum, actually, it is that case. The other one (CRTSCTS and gpios) is
handled in the else below. I think you need to keep the termios->c_cflag
&= ~CRTSCTS; here so that userspace knows configuring it failed.

quoted

quoted

      } else {
              /* RS232 without hadware handshake or controlled by GPIOs */
              mode |= ATMEL_US_USMODE_NORMAL;

-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com