All, > -----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. Tested with Atmel AT91SAM9G25 with nine devices connected to USART0 at 9600 baud, three devices connected to USART1 at 115200 baud, and two devices connected to USART3 at 115200 baud. Verified with v4.4.61 that TX and RX DMA works on all three serial ports with the patch, and without the patch that data transactions fail when DMA is enabled. Tested port open/close, power cycling the system and rebooting, and in all cases, all ports remained operational with the patch. With v4.1.39, TX DMA works on all three serial ports with the patch, and without the patch all transactions fail with TX DMA enabled. I was unable to use both RX and TX DMA with v4.1.39 even with the patch. However, there are several other patches in v4.4 related to Atmel's serial DMA that are not in v4.1, which from my testing looks to be the reason why I can't operate with both RX and TX DMA with v4.1.39. For today's purpose, the patch does fix the listed issue on v4.1.39. Tested-by: Bryan Evenson <bevenson@xxxxxxxxxxxxxx> > > 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