On 09.06.20 09:23, Schrempf Frieder wrote:
> From: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
>
> commit 1866541492641c02874bf51f9d8712b5510f2c64 upstream
>
> When using RS485 half duplex the Transmitter Complete irq is needed to
> determine the moment when the transmitter can be disabled. When using
> DMA this irq must only be enabled when DMA has completed to transfer all
> data. Otherwise the CPU might busily trigger this irq which is not
> properly handled and so the also pending irq for the DMA transfer cannot
> trigger.
>
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.14.x
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> [Backport to v4.14]
> Signed-off-by: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx>
> ---
Sorry, forgot the changelog:
Changes for backport v2:
* Remove an unrelated additional blank line.
> When using RS485 with DMA enabled simply transmitting some data on our
> i.MX6ULL based boards often freezes the system completely. The higher
> the baudrate, the easier it is to reproduce the issue. To test this I
> simply used:
>
> stty -F /dev/ttymxc1 speed 115200
> while true; do echo TEST > /dev/ttymxc1; done
>
> Without the patch this leads to an almost immediate system freeze,
> with the patch applied, everything keeps working as expected.
> ---
> drivers/tty/serial/imx.c | 22 ++++++++++++++++++----
> 1 file changed, 18 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index 3f2605edd855..70c737236870 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -538,6 +538,11 @@ static void dma_tx_callback(void *data)
>
> if (!uart_circ_empty(xmit) && !uart_tx_stopped(&sport->port))
> imx_dma_tx(sport);
> + else if (sport->port.rs485.flags & SER_RS485_ENABLED) {
> + temp = readl(sport->port.membase + UCR4);
> + temp |= UCR4_TCEN;
> + writel(temp, sport->port.membase + UCR4);
> + }
>
> spin_unlock_irqrestore(&sport->port.lock, flags);
> }
> @@ -555,6 +560,10 @@ static void imx_dma_tx(struct imx_port *sport)
> if (sport->dma_is_txing)
> return;
>
> + temp = readl(sport->port.membase + UCR4);
> + temp &= ~UCR4_TCEN;
> + writel(temp, sport->port.membase + UCR4);
> +
> sport->tx_bytes = uart_circ_chars_pending(xmit);
>
> if (xmit->tail < xmit->head || xmit->head == 0) {
> @@ -617,10 +626,15 @@ static void imx_start_tx(struct uart_port *port)
> if (!(port->rs485.flags & SER_RS485_RX_DURING_TX))
> imx_stop_rx(port);
>
> - /* enable transmitter and shifter empty irq */
> - temp = readl(port->membase + UCR4);
> - temp |= UCR4_TCEN;
> - writel(temp, port->membase + UCR4);
> + /*
> + * Enable transmitter and shifter empty irq only if DMA is off.
> + * In the DMA case this is done in the tx-callback.
> + */
> + if (!sport->dma_is_enabled) {
> + temp = readl(port->membase + UCR4);
> + temp |= UCR4_TCEN;
> + writel(temp, port->membase + UCR4);
> + }
> }
>
> if (!sport->dma_is_enabled) {
>
