Re: [PATCH] tty/serial: atmel_serial: BUG: stop DMA from transmitting in stop_tx
From: Nicolas Ferre
Date: Mon Jan 02 2017 - 06:13:39 EST
Le 13/12/2016 à 17:27, Richard Genoud a écrit :
> If we don't disable the transmitter in atmel_stop_tx, the DMA buffer
> continues to send data until it is emptied.
> This cause problems with the flow control (CTS is asserted and data are
> still sent).
>
> So, disabling the transmitter in atmel_stop_tx is a sane thing to do.
>
> Tested on at91sam9g35-cm(DMA)
> Tested for regressions on sama5d2-xplained(Fifo) and at91sam9g20ek(PDC)
>
> Cc: <stable@xxxxxxxxxxxxxxx> (beware, this won't apply before 4.3)
> Signed-off-by: Richard Genoud <richard.genoud@xxxxxxxxx>
Acked-by: Nicolas Ferre <nicolas.ferre@xxxxxxxxx>
> ---
> drivers/tty/serial/atmel_serial.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> NB: this is not for the 4.10 merge window, I'm just sending it now to
> have some comments if someone is againts it.
>
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index 168b10cad47b..f9d42de5ab2d 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -481,6 +481,14 @@ static void atmel_stop_tx(struct uart_port *port)
> /* disable PDC transmit */
> atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTDIS);
> }
> +
> + /*
> + * Disable the transmitter.
> + * This is mandatory when DMA is used, otherwise the DMA buffer
> + * is fully transmitted.
> + */
> + atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXDIS);
> +
> /* Disable interrupts */
> atmel_uart_writel(port, ATMEL_US_IDR, atmel_port->tx_done_mask);
>
> @@ -513,6 +521,9 @@ static void atmel_start_tx(struct uart_port *port)
>
> /* Enable interrupts */
> atmel_uart_writel(port, ATMEL_US_IER, atmel_port->tx_done_mask);
> +
> + /* re-enable the transmitter */
> + atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN);
> }
>
> /*
>
--
Nicolas Ferre