From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Genoud Subject: [PATCH] tty/serial: atmel: RS485 half duplex w/DMA: enable RX after TX is done Date: Tue, 6 Dec 2016 13:05:33 +0100 Message-ID: <20161206120533.14505-1-richard.genoud@gmail.com> Return-path: Sender: linux-kernel-owner@vger.kernel.org To: Greg KH Cc: Gil Weber , Alexandre Belloni , Nicolas Ferre , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Richard Genoud , stable@vger.kernel.org List-Id: linux-serial@vger.kernel.org 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 Tested-by: Gil Weber Signed-off-by: Richard Genoud --- drivers/tty/serial/atmel_serial.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c index 168b10cad47b..11c0117af80b 100644 --- a/drivers/tty/serial/atmel_serial.c +++ b/drivers/tty/serial/atmel_serial.c @@ -798,6 +798,11 @@ 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); } @@ -900,12 +905,6 @@ 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)