Re: [PATCH v5 3/4] serial: sh-sci: Fix fallback to PIO in sci_dma_rx_complete()

[Ulrich Hecht <uli@fpond.eu>]

> On January 7, 2019 at 5:23 PM Geert Uytterhoeven <geert+renesas@glider.be> wrote:
> 
> 
> When submitting a DMA request fails in sci_dma_rx_complete(), the driver
> tries to fall back to PIO, but that does not work: no more data will be
> received, or the kernel will even crash.
> 
> Fix this similar as in (but not identical to) sci_submit_rx():
>   - On SCIF, PIO cannot take over if any DMA transactions are pending,
>     hence they must be terminated first.
>   - All active cookies must be invalidated, else rx_timer_fn() may
>     trigger a NULL pointer dereference.
>   - Restarting the port is not needed, as it is already running, but
>     serial port interrupts must be directed back from the DMA engine to
>     the CPU.
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
> v5:
>   - Call new helpers sci_dma_rx_chan_invalidate() and
>     sci_dma_rx_reenable_irq() instead of open-coding,
> 
> v4:
>   - No changes,
> 
> v3:
>   - Add missing definition of "u16 scr",
>   - Move call to dmaengine_terminate_async() inside the spinlock, for
>     symmetry with sci_submit_rx(),
>   - Split in multiple patches.
> ---
>  drivers/tty/serial/sh-sci.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
> index 4d814c30c4189b56..891833315698b953 100644
> --- a/drivers/tty/serial/sh-sci.c
> +++ b/drivers/tty/serial/sh-sci.c
> @@ -1337,8 +1337,9 @@ static void sci_dma_rx_complete(void *arg)
>  	dev_warn(port->dev, "Failed submitting Rx DMA descriptor\n");
>  	/* Switch to PIO */
>  	spin_lock_irqsave(&port->lock, flags);
> -	s->chan_rx = NULL;
> -	sci_start_rx(port);
> +	dmaengine_terminate_async(chan);
> +	sci_dma_rx_chan_invalidate(s);
> +	sci_dma_rx_reenable_irq(s);
>  	spin_unlock_irqrestore(&port->lock, flags);
>  }
>  
> -- 
> 2.17.1
>

Reviewed-by: Ulrich Hecht <uli+renesas@fpond.eu>

CU
Uli