[ adding Gil Weber in Cc: ] Le 15/03/2019 à 10:23, Razvan Stefanescu a écrit : > In half-duplex operation, RX should be started after TX completes. > > If DMA is used, there is a case when the DMA transfer completes but the > TX FIFO is not emptied, so the RX cannot be restarted just yet. > > Use a boolean variable to store this state and rearm TX interrupt mask > to be signaled again that the transfer finished. In interrupt transmit > handler this variable is used to start RX. I was sure I've already seen something like that. Gil, could you give it a test ? you can add : Cc: stable@xxxxxxxxxxxxxxx Fixes: b389f173aaa1 ("tty/serial: atmel: RS485 half duplex w/DMA: enable RX after TX is done") Since patch 1/2 is needed for this one, I think you should add also Cc:stable / Fixes: to the previous patch. > Signed-off-by: Razvan Stefanescu <razvan.stefanescu@xxxxxxxxxxxxx> > --- > drivers/tty/serial/atmel_serial.c | 25 ++++++++++++++++++++++--- > 1 file changed, 22 insertions(+), 3 deletions(-) > > diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c > index a6577b1c4461..b0141dcbbb61 100644 > --- a/drivers/tty/serial/atmel_serial.c > +++ b/drivers/tty/serial/atmel_serial.c > @@ -166,6 +166,8 @@ struct atmel_uart_port { > unsigned int pending_status; > spinlock_t lock_suspended; > > + bool hd_start_rx; /* can start RX during half-duplex operation */ > + > /* ISO7816 */ > unsigned int fidi_min; > unsigned int fidi_max; > @@ -934,8 +936,13 @@ static void atmel_complete_tx_dma(void *arg) > if (!uart_circ_empty(xmit)) > atmel_tasklet_schedule(atmel_port, &atmel_port->tasklet_tx); > else if (atmel_uart_is_half_duplex(port)) { > - /* DMA done, stop TX, start RX for RS485 */ > - atmel_start_rx(port); > + /* > + * DMA done, re-enable TXEMPTY and signal that we can stop > + * TX and start RX for RS485 > + */ > + atmel_port->hd_start_rx = true; > + atmel_uart_writel(port, ATMEL_US_IER, > + atmel_port->tx_done_mask); > } > > spin_unlock_irqrestore(&port->lock, flags); > @@ -1379,9 +1386,21 @@ atmel_handle_transmit(struct uart_port *port, unsigned int pending) > struct atmel_uart_port *atmel_port = to_atmel_uart_port(port); > > if (pending & atmel_port->tx_done_mask) { > - /* Either PDC or interrupt transmission */ > atmel_uart_writel(port, ATMEL_US_IDR, > atmel_port->tx_done_mask); > + > + /* Start RX if flag was set and FIFO is empty */ > + if (atmel_port->hd_start_rx) { > + if (atmel_uart_readl(port, ATMEL_US_CSR) > + & ATMEL_US_TXEMPTY) { > + atmel_port->hd_start_rx = false; > + atmel_start_rx(port); > + } else { > + dev_warn(port->dev, "Should start RX, but TX fifo is not empty\n"); What will happen in this case ? > + } > + return; > + } > + > atmel_tasklet_schedule(atmel_port, &atmel_port->tasklet_tx); > } > } > Thanks !