Le 19/03/2019 à 14:20, 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. A warning message is generated
> if RX is activated before TX fifo is cleared.
>
> Fixes: b389f173aaa1 ("tty/serial: atmel: RS485 half duplex w/DMA: enable
> RX after TX is done")
> Signed-off-by: Razvan Stefanescu <razvan.stefanescu@xxxxxxxxxxxxx>
Acked-by: Richard Genoud <richard.genoud@xxxxxxxxx>
NB: backport on kernel older than 4.20 will fail because of the iso7816
variables fidi_min/fidi_max.
> ---
> Changelog:
> v2:
> - start RX and display warning in case of error
> - add fix info
>
> 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 b4b89a16a41b..5b2f859c327c 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;
> @@ -933,8 +935,13 @@ 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);
> @@ -1378,9 +1385,20 @@ 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))
> + dev_warn(port->dev, "Should start RX, but TX fifo is not empty\n");
> +
> + atmel_port->hd_start_rx = false;
> + atmel_start_rx(port);
> + return;
> + }
> +
> atmel_tasklet_schedule(atmel_port, &atmel_port->tasklet_tx);
> }
> }
>
