tty/serial: atmel: RS485 half duplex w/DMA: enable RX after TX is done

When using RS485 in half duplex, RX should be enabled when TX is
finished, and stopped when TX starts.

Before commit 0058f0871efe7b01c6 ("tty/serial: atmel: fix RS485 half
duplex with DMA"), RX was not disabled in atmel_start_tx() if the DMA
was used. So, collisions could happened.

But disabling RX in atmel_start_tx() uncovered another bug:
RX was enabled again in the wrong place (in atmel_tx_dma) instead of
being enabled when TX is finished (in atmel_complete_tx_dma), so the
transmission simply stopped.

This bug was not triggered before commit 0058f0871efe7b01c6
("tty/serial: atmel: fix RS485 half duplex with DMA") because RX was
never disabled before.

Moving atmel_start_rx() in atmel_complete_tx_dma() corrects the problem.

Cc: stable@vger.kernel.org
Reported-by: Gil Weber <webergil@gmail.com>
Fixes: 0058f0871efe7b01c6
Tested-by: Gil Weber <webergil@gmail.com>
Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 5 insertions, 6 deletions

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index f9d42de5ab2d..fabbe76203bb 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -809,6 +809,11 @@ static void atmel_complete_tx_dma(void *arg)
          */
         if (!uart_circ_empty(xmit))
                 atmel_tasklet_schedule(atmel_port, &atmel_port->tasklet_tx);
+        else if ((port->rs485.flags & SER_RS485_ENABLED) &&
+                 !(port->rs485.flags & SER_RS485_RX_DURING_TX)) {
+                /* DMA done, stop TX, start RX for RS485 */
+                atmel_start_rx(port);
+        }
 
         spin_unlock_irqrestore(&port->lock, flags);
 }
@@ -911,12 +916,6 @@ static void atmel_tx_dma(struct uart_port *port)
                 desc->callback = atmel_complete_tx_dma;
                 desc->callback_param = atmel_port;
                 atmel_port->cookie_tx = dmaengine_submit(desc);
-
-        } else {
-                if (port->rs485.flags & SER_RS485_ENABLED) {
-                        /* DMA done, stop TX, start RX for RS485 */
-                        atmel_start_rx(port);
-                }
         }
 
         if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)