On Wed, Sep 10, 2014 at 09:30:07PM +0200, Sebastian Andrzej Siewior wrote:
> Sometimes the OMAP UART does not signal the DMA engine to unload the FIFO.
> Usually this happens when we have >threshold bytes in the FIFO
> and start the DMA transfer. It seems that in those cases the UART won't
> trigger the transfer once the requested threshold is reached. In some
> rare cases the UART does not trigger the DMA transfer even if programmed
> while the FIFO was empty.
> In those cases the UART drops an RDI event and we have to empty the FIFO
> manually. If we ignore it because the DMA transfer is programmed then we
> will enter the function a few times until we receive the RX_TIMEOUT
> event. At that point the FIFO is usually full and we risk to overflow
> the FIFO.
>
> Reviewed-by: Tony Lindgren <tony@xxxxxxxxxxx>
> Tested-by: Tony Lindgren <tony@xxxxxxxxxxx>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
> drivers/tty/serial/8250/8250_dma.c | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
> index fa1dc966f394..898a6781d0b3 100644
> --- a/drivers/tty/serial/8250/8250_dma.c
> +++ b/drivers/tty/serial/8250/8250_dma.c
> @@ -193,6 +193,24 @@ int serial8250_rx_dma(struct uart_8250_port *p, unsigned int iir)
> __dma_rx_do_complete(p, true);
> }
> return -ETIMEDOUT;
> + case UART_IIR_RDI:
> + if (p->bugs & UART_BUG_DMA_RX)
> + break;
> + /*
> + * The OMAP UART is a special BEAST. If we receive RDI we _have_
> + * a DMA transfer programmed but it didn't worked. One reason is
didn't work
> + * that we were too slow and there were too many bytes in the
> + * FIFO, the UART counted wrong and never kicked the DMA engine
> + * to do anything. That means once we receive RDI on OMAP than
then
> + * the DMA won't do anything soon so we have to cancel the DMA
> + * transfer and purge the FIFO manually.
> + */
> + if (dma->rx_running) {
> + dmaengine_pause(dma->rxchan);
> + __dma_rx_do_complete(p, true);
> + }
> + return -ETIMEDOUT;
> +
> default:
> break;
> }
> --
> 2.1.0
>
>
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