Re: [PATCH] serial: 8250_omap: clear rx_running on zero-length DMA completes

[Moteen Shah]

Hey Matthias,
Thanks for the patch.

On 21/05/26 19:00, Matthias Feser wrote:
> On AM33xx RX DMA only triggers when the FIFO reaches the
> configured threshold (typically 48 bytes). For smaller bursts
> no DMA request is issued and the FIFO is drained by RX timeout.
>
> In this case __dma_rx_do_complete() can legitimately see count == 0.
>
> The current code exits early in this case and does not clear
> dma->rx_running, leaving the DMA state inconsistent. This can
> prevent RX DMA from restarting and may cause
> omap_8250_rx_dma_flush() to fail, marking DMA as broken.
>
> Fix this by always clearing dma->rx_running on exit.
>
> Signed-off-by: Matthias Feser <mfe@xxxxxxxxxxxxxxxxxxxxxxxxx>
> ---
>   drivers/tty/serial/8250/8250_omap.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
> index c552c6b9a037..686e54859aa5 100644
> --- a/drivers/tty/serial/8250/8250_omap.c
> +++ b/drivers/tty/serial/8250/8250_omap.c
> @@ -948,11 +948,11 @@ static void __dma_rx_do_complete(struct uart_8250_port *p)
>   		goto out;
>   	ret = tty_insert_flip_string(tty_port, dma->rx_buf, count);
>   
> -	dma->rx_running = 0;
>   	p->port.icount.rx += ret;
>   	p->port.icount.buf_overrun += count - ret;
>   out:
>   
> +	dma->rx_running = 0;
>   	tty_flip_buffer_push(tty_port);
>   }
>   

I think the better place should be just before the If(!count) check, 
this would mark the running status of the DMA as soon as the termination 
gets done.

Regards,
Moteen