linux-kernel - Re: [PATCH v3 2/2] dma: pl330: add DMA

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Message-ID: <20150211002405.GC21387@intel.com>
Date:	Tue, 10 Feb 2015 16:24:05 -0800
From:	Vinod Koul <vinod.koul@...el.com>
To:	Robert Baldyga <r.baldyga@...sung.com>
Cc:	dan.j.williams@...el.com, lars@...afoo.de,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	m.szyprowski@...sung.com, k.kozlowski@...sung.com,
	kyungmin.park@...sung.com, l.czerwinski@...sung.com,
	padma.kvr@...il.com
Subject: Re: [PATCH v3 2/2] dma: pl330: add DMA_PAUSE feature

On Wed, Dec 10, 2014 at 11:55:18AM +0100, Robert Baldyga wrote:
> DMA_PAUSE command is used for halting DMA transfer on chosen channel.
> It can be useful when we want to safely read residue before terminating
> all requests on channel. Otherwise there can be situation when some data
> is transferred before channel termination but after reading residue,
> which obviously results with data loss. To avoid this situation we can
> pause channel, read residue and then terminate all requests.
> This scenario is common, for example, in serial port drivers.
And where is the resume here? Also this needs rebase

-- 
~Vinod

> 
> Signed-off-by: Robert Baldyga <r.baldyga@...sung.com>
> ---
>  drivers/dma/pl330.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
> index 2f4d561..ead4369 100644
> --- a/drivers/dma/pl330.c
> +++ b/drivers/dma/pl330.c
> @@ -2137,6 +2137,25 @@ static int pl330_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd, unsigned
>  		pm_runtime_mark_last_busy(pl330->ddma.dev);
>  		pm_runtime_put_autosuspend(pl330->ddma.dev);
>  		break;
> +	case DMA_PAUSE:
> +		/*
> +		 * We don't support DMA_RESUME command because of hardware
> +		 * limitations, so after pausing the channel we cannot restore
> +		 * it to active state. We have to terminate channel and setup
> +		 * DMA transfer again. This pause feature was implemented to
> +		 * allow safely read residue before channel termination.
> +		 */
> +		pm_runtime_get_sync(pl330->ddma.dev);
> +		spin_lock_irqsave(&pch->lock, flags);
> +
> +		spin_lock(&pl330->lock);
> +		_stop(pch->thread);
> +		spin_unlock(&pl330->lock);
> +
> +		spin_unlock_irqrestore(&pch->lock, flags);
> +		pm_runtime_mark_last_busy(pl330->ddma.dev);
> +		pm_runtime_put_autosuspend(pl330->ddma.dev);
> +		break;
>  	case DMA_SLAVE_CONFIG:
>  		slave_config = (struct dma_slave_config *)arg;
>  
> -- 
> 1.9.1
> 

-- 
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