4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Richard Genoud <richard.genoud@xxxxxxxxx> commit b389f173aaa1204d6dc1f299082a162eb0491545 upstream. 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. Reported-by: Gil Weber <webergil@xxxxxxxxx> Fixes: 0058f0871efe7b01c6 Tested-by: Gil Weber <webergil@xxxxxxxxx> Signed-off-by: Richard Genoud <richard.genoud@xxxxxxxxx> Acked-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxxxxxxxxx> Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxxxxxxxxx> Tested-by: Bryan Evenson <bevenson@xxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/tty/serial/atmel_serial.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) --- a/drivers/tty/serial/atmel_serial.c +++ b/drivers/tty/serial/atmel_serial.c @@ -810,6 +810,11 @@ static void atmel_complete_tx_dma(void * */ if (!uart_circ_empty(xmit)) tasklet_schedule(&atmel_port->tasklet); + 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); } @@ -912,12 +917,6 @@ static void atmel_tx_dma(struct uart_por 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)