Re: [PATCH v2] serial: 8250_omap: clear rx_running on zero-length DMA completes

["gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>]

On Fri, May 22, 2026 at 08:24:01AM +0000, Matthias Feser wrote:
> Thanks for the fast response. I've updated the patch accordingly.
> 
> From: Matthias Feser <mfe@KBSgmbhfr.onmicrosoft.com>
> Date: Fri, 22 May 2026 10:11:16 +0200
> Subject: [PATCH v2] serial: 8250_omap: clear rx_running on zero-length DMA completes
> 
> 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 clearing dma->rx_running once the DMA transfer has
> completed or been terminated, even if no data was transferred.
> 
> Changes in v2:
> - Move dma->rx_running clear before the count check so the state
>   is updated immediately after DMA completion/termination
> 
> Signed-off-by: Matthias Feser <mfe@KBSgmbhfr.onmicrosoft.com>
> ---
>  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..76bc8ad324cb 100644
> --- a/drivers/tty/serial/8250/8250_omap.c
> +++ b/drivers/tty/serial/8250/8250_omap.c
> @@ -944,11 +944,11 @@ static void __dma_rx_do_complete(struct uart_8250_port *p)
>  				dev_err(p->port.dev, "teardown incomplete\n");
>  		}
>  	}
> +	dma->rx_running = 0;
>  	if (!count)
>  		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:
> -- 
> 2.39.5
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
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created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
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