On Fri, 16 Jun 2023, Martin Fuzzey wrote:
> Since commit 79d0224f6bf2 ("tty: serial: imx: Handle RS485 DE signal
> active high") RS485 reception no longer works after a transmission.
>
> The following scenario shows the problem:
> 1) Open a port in RS485 mode
> 2) Receive data from remote (OK)
> 3) Transmit data to remote (OK)
> 4) Receive data from remote (Nothing received)
>
> In RS485 mode, imx_uart_start_tx() calls imx_uart_stop_rx() and, when the
> transmission is complete, imx_uart_stop_tx() calls imx_uart_start_rx().
>
> Since the above commit imx_uart_stop_rx() now sets the loopback bit but
> imx_uart_start_rx() does not clear it causing the hardware to remain in
> loopback mode and not receive external data.
>
> Fix this by moving the existing loopback disable code to a helper function
> and calling it from imx_uart_start_rx() too.
>
> Fixes: 79d0224f6bf2 ("tty: serial: imx: Handle RS485 DE signal active high")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Martin Fuzzey <martin.fuzzey@flowbird.group>
> ---
> drivers/tty/serial/imx.c | 18 +++++++++++++-----
> 1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index c5e17569c3ad..3fe8ff241522 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -369,6 +369,16 @@ static void imx_uart_soft_reset(struct imx_port *sport)
> sport->idle_counter = 0;
> }
>
> +static void imx_uart_disable_loopback_rs485(struct imx_port *sport)
> +{
> + unsigned int uts;
> +
> + /* See SER_RS485_ENABLED/UTS_LOOP comment in imx_uart_probe() */
> + uts = imx_uart_readl(sport, imx_uart_uts_reg(sport));
> + uts &= ~UTS_LOOP;
> + imx_uart_writel(sport, uts, imx_uart_uts_reg(sport));
> +}
> +
> /* called with port.lock taken and irqs off */
> static void imx_uart_start_rx(struct uart_port *port)
> {
> @@ -390,6 +400,7 @@ static void imx_uart_start_rx(struct uart_port *port)
> /* Write UCR2 first as it includes RXEN */
> imx_uart_writel(sport, ucr2, UCR2);
> imx_uart_writel(sport, ucr1, UCR1);
> + imx_uart_disable_loopback_rs485(sport);
> }
>
> /* called with port.lock taken and irqs off */
> @@ -1422,7 +1433,7 @@ static int imx_uart_startup(struct uart_port *port)
> int retval;
> unsigned long flags;
> int dma_is_inited = 0;
> - u32 ucr1, ucr2, ucr3, ucr4, uts;
> + u32 ucr1, ucr2, ucr3, ucr4;
>
> retval = clk_prepare_enable(sport->clk_per);
> if (retval)
> @@ -1521,10 +1532,7 @@ static int imx_uart_startup(struct uart_port *port)
> imx_uart_writel(sport, ucr2, UCR2);
> }
>
> - /* See SER_RS485_ENABLED/UTS_LOOP comment in imx_uart_probe() */
> - uts = imx_uart_readl(sport, imx_uart_uts_reg(sport));
> - uts &= ~UTS_LOOP;
> - imx_uart_writel(sport, uts, imx_uart_uts_reg(sport));
> + imx_uart_disable_loopback_rs485(sport);
>
> spin_unlock_irqrestore(&sport->port.lock, flags);
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
--
i.
