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SubjectRe: [PATCH] serial: imx: Improve PIO prevention if TX DMA has been started
On Sat, Aug 12, 2017 at 05:12:10PM +0200, Clemens Gruber wrote:
> The imx_transmit_buffer function should return if TX DMA has already
> been started and not just skip over the buffer PIO write loop. (Which
> did fix the initial problem, but could have unintentional side-effects)
>
> Tested on an i.MX6Q board with half-duplex RS-485 and with RS-232.
>
> Cc: Ian Jamison <ian.dev@arkver.com>
> Cc: Uwe-Kleine König <u.kleine-koenig@pengutronix.de>
> Fixes: 514ab34dbad6 ("serial: imx: Prevent TX buffer PIO write when a
> DMA has been started")

AFAIK no newline in the Fixes: line.

> Signed-off-by: Clemens Gruber <clemens.gruber@pqgruber.com>
> ---
> drivers/tty/serial/imx.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index 80934e7bd67f..fce538eb8c77 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -452,13 +452,14 @@ static inline void imx_transmit_buffer(struct imx_port *sport)
> if (sport->dma_is_txing) {
> temp |= UCR1_TDMAEN;
> writel(temp, sport->port.membase + UCR1);
> + return;
> } else {
> writel(temp, sport->port.membase + UCR1);
> imx_dma_tx(sport);
> }

Shouldn't the return go here?

Did you understand the problem? Can you say why this only hurts in RS485
half-duplex but not (as it seems) in regular rs232 mode?

> }
>
> - while (!uart_circ_empty(xmit) && !sport->dma_is_txing &&
> + while (!uart_circ_empty(xmit) &&
> !(readl(sport->port.membase + uts_reg(sport)) & UTS_TXFULL)) {
> /* send xmit->buf[xmit->tail]
> * out the port here */

Best regards
Uwe

--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |

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