Alexandre, > -----Original Message----- > From: Alexandre Belloni [mailto:alexandre.belloni@xxxxxxxxxxxxxxxxxx] > Sent: Tuesday, April 11, 2017 5:06 PM > To: Bryan Evenson <bevenson@xxxxxxxxxxxxxx>; Greg Kroah-Hartman > <gregkh@xxxxxxxxxxxxxxxxxxx>; Richard Genoud > <richard.genoud@xxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx; Alexandre Belloni <alexandre.belloni@free- > electrons.com> > Subject: [PATCH] tty/serial: atmel: RS485 half duplex w/DMA: enable RX after > TX is done > > 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. > > Cc: stable@xxxxxxxxxxxxxxx > 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: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxxxxxxxxx> > --- > > Hi, this is b389f173aaa1204d6dc1f299082a162eb0491545 backported to v4.4 > and v4.1 > > Note: this has only been build tested. Bryan, please test. Initially looks good, but I'm running a few more tests for completeness. I should have a final answer later today. Bryan > > 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 a15070a7fcd6..53e4d5056db7 100644 > --- 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 *arg) > */ > 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_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) > -- > 2.11.0