linux-kernel - Re: [PATCH v1 06/12] serial: 8250_dma: stop ongoing RX DMA on exception

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Date:	Thu, 7 Apr 2016 16:54:13 -0700
From:	Peter Hurley <peter@...leysoftware.com>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	Vinod Koul <vinod.koul@...el.com>, linux-kernel@...r.kernel.org,
	dmaengine@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	ismo.puustinen@...el.com,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH v1 06/12] serial: 8250_dma: stop ongoing RX DMA on
 exception

On 04/07/2016 01:37 PM, Andy Shevchenko wrote:
> If we get an exeption interrupt. i.e. UART_IIR_RLSI, stop any ongoing RX DMA
> transfer otherwise it might generates more spurious interrupts and make port
> unavailable anymore.

Then how to know which rx byte the error is for if dma continues anyway?
What if there are multiple error bytes?


> As has been seen on Intel Broxton system:

This system shouldn't be setup for UART DMA imo.


> ...
> [  168.526281] serial8250: too much work for irq5
> [  168.535908] serial8250: too much work for irq5
> [  173.449464] serial8250_interrupt: 4439 callbacks suppressed
> [  173.455694] serial8250: too much work for irq5
> ...
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  drivers/tty/serial/8250/8250_dma.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
> index 9d80bb1..b134bec 100644
> --- a/drivers/tty/serial/8250/8250_dma.c
> +++ b/drivers/tty/serial/8250/8250_dma.c
> @@ -110,6 +110,16 @@ err:
>  	return ret;
>  }
>  
> +static void __dma_rx_stop(struct uart_8250_port *p, struct uart_8250_dma *dma)
> +{
> +	if (!dma->rx_running)
> +		return;
> +
> +	dmaengine_pause(dma->rxchan);
> +	__dma_rx_complete(p);
> +	dmaengine_terminate_async(dma->rxchan);
> +}
> +
>  int serial8250_rx_dma(struct uart_8250_port *p, unsigned int iir)
>  {
>  	struct uart_8250_dma		*dma = p->dma;
> @@ -118,17 +128,14 @@ int serial8250_rx_dma(struct uart_8250_port *p, unsigned int iir)
>  	switch (iir & 0x3f) {
>  	case UART_IIR_RLSI:
>  		/* 8250_core handles errors and break interrupts */
> +		__dma_rx_stop(p, dma);
>  		return -EIO;
>  	case UART_IIR_RX_TIMEOUT:
>  		/*
>  		 * If RCVR FIFO trigger level was not reached, complete the
>  		 * transfer and let 8250_core copy the remaining data.
>  		 */
> -		if (dma->rx_running) {
> -			dmaengine_pause(dma->rxchan);
> -			__dma_rx_complete(p);
> -			dmaengine_terminate_async(dma->rxchan);
> -		}
> +		__dma_rx_stop(p, dma);
>  		return -ETIMEDOUT;
>  	default:
>  		break;
>