Re: [PATCH v4 7/9] dma: dw: Avoid partial transfers

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

+Cc: Ilpo who is currently doing adjoining stuff.

Ilpo, this one affects Intel Bay Trail and Cherry Trail platforms.
Not sure if it's in scope of your interest right now, but it might
be useful to see how DMA <--> 8250 UART functioning.

On Thu, Mar 10, 2022 at 04:57:53PM +0100, Miquel Raynal wrote:
> As investigated by Phil Edworthy <phil.edworthy@renesas.com> on RZN1 a

Email can be dropped as you put it below, just (full) name is enough.

I'm wondering if Phil or anybody else who possess the hardware can
test / tested this.

> while ago, pausing a partial transfer only causes data to be written to
> memory that is a multiple of the memory width setting. Such a situation
> can happen eg. because of a char timeout interrupt on a UART. In this
> case, the current ->terminate_all() implementation does not always flush
> the remaining data as it should.
> 
> In order to workaround this, a solutions is to resume and then pause
> again the transfer before termination. The resume call in practice
> actually flushes the remaining data.

Perhaps Fixes tag?

> Reported-by: Phil Edworthy <phil.edworthy@renesas.com>
> Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> ---
>  drivers/dma/dw/core.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
> index 7ab83fe601ed..2f6183177ba5 100644
> --- a/drivers/dma/dw/core.c
> +++ b/drivers/dma/dw/core.c
> @@ -862,6 +862,10 @@ static int dwc_terminate_all(struct dma_chan *chan)
>  
>  	clear_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags);
>  
> +	/* Ensure the last byte(s) are drained before disabling the channel */
> +	if (test_bit(DW_DMA_IS_PAUSED, &dwc->flags))
> +		dwc_chan_resume(dwc, true);
> +
>  	dwc_chan_pause(dwc, true);
>  
>  	dwc_chan_disable(dw, dwc);
> -- 
> 2.27.0
> 

-- 
With Best Regards,
Andy Shevchenko