linux-kernel - Re: [PATCH 1/1] dma: imx-sdma: add 1ms delay to ensure SDMA channel is stopped

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Date:   Mon, 13 Feb 2017 07:35:30 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     jiada_wang@...tor.com
Cc:     dan.j.williams@...el.com, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] dma: imx-sdma: add 1ms delay to ensure SDMA channel
 is stopped

On Fri, Feb 10, 2017 at 06:46:45AM -0800, jiada_wang@...tor.com wrote:
> From: Jiada Wang <jiada_wang@...tor.com>
> 
> sdma_disable_channel() cannot ensure dma is stopped to access
> module's FIFOs. Maybe SDMA core is running and accessing BD when
> disable of corresponding channel, this may cause sometimes even
> after call of .sdma_disable_channel(), SDMA core still be running
> and accessing module's FIFOs.
> 
> We should add delay of one BD SDMA cost time, the maximum is 1ms.
> So that SDMA clients by calling .device_terminate_all can
> ensure SDMA core has really been stopped.
> 
> Signed-off-by: Jiada Wang <jiada_wang@...tor.com>
> ---
>  drivers/dma/imx-sdma.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> index d1651a5..7332c40 100644
> --- a/drivers/dma/imx-sdma.c
> +++ b/drivers/dma/imx-sdma.c
> @@ -937,6 +937,14 @@ static int sdma_disable_channel(struct dma_chan *chan)
>  	return 0;
>  }
>  
> +static int sdma_disable_channel_with_delay(struct dma_chan *chan)
> +{
> +	sdma_disable_channel(chan);
> +	mdelay(1);

what is the gaurantee that 1ms is fine? Shouldn't you poll the bit to see
channel is disabled properly..

> +
> +	return 0;
> +}
> +
>  static void sdma_set_watermarklevel_for_p2p(struct sdma_channel *sdmac)
>  {
>  	struct sdma_engine *sdma = sdmac->sdma;
> @@ -1828,7 +1836,7 @@ static int sdma_probe(struct platform_device *pdev)
>  	sdma->dma_device.device_prep_slave_sg = sdma_prep_slave_sg;
>  	sdma->dma_device.device_prep_dma_cyclic = sdma_prep_dma_cyclic;
>  	sdma->dma_device.device_config = sdma_config;
> -	sdma->dma_device.device_terminate_all = sdma_disable_channel;
> +	sdma->dma_device.device_terminate_all = sdma_disable_channel_with_delay;
>  	sdma->dma_device.src_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_4_BYTES);
>  	sdma->dma_device.dst_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_4_BYTES);
>  	sdma->dma_device.directions = BIT(DMA_DEV_TO_MEM) | BIT(DMA_MEM_TO_DEV);
> -- 
> 2.7.4
> 
> 

-- 
~Vinod