linux-kernel - Re: [PATCH 1/2] dma: Add interface to calculate data transferred

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Date:	Fri, 11 Oct 2013 10:22:15 +0000
From:	"Shevchenko, Andriy" <andriy.shevchenko@...el.com>
To:	"Song, Youquan" <youquan.song@...el.com>
CC:	"Williams, Dan J" <dan.j.williams@...el.com>,
	"Koul, Vinod" <vinod.koul@...el.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"Westerberg, Mika" <mika.westerberg@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Youquan Song <youquan.song@...ux.intel.com>
Subject: Re: [PATCH 1/2] dma: Add interface to calculate data transferred

On Fri, 2013-10-11 at 17:42 -0400, Youquan Song wrote:
> Currently, the DMA channel calculates its data transferred only at network
> device driver. When other devices like UART or SPI etc, transfers data by DMA 
> mode, but it always shows 0 at /sys/class/dma/dma0chan*/bytes_transferred.
> 
> This patch add a new function which will calculate how many the data has been
> transferred after doing it by DMA mode. It can be used by other modules and
> also simplify current duplicated code.

Thanks for the patch. My comments below.

First of all, what is the point to have every device driver that uses
DMA to increment bytes_transferred value? It will show just amount of
data transferred through certain channel. How it could be used then?

> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -901,6 +901,23 @@ void dma_async_device_unregister(struct dma_device *device)
>  }
>  EXPORT_SYMBOL(dma_async_device_unregister);
>  
> +dma_cookie_t
> +dma_tx_submit_cal(struct dma_async_tx_descriptor *tx,
> +		struct dma_chan *chan, size_t len)

I think there is a better name for the function.
dmaengine_submit_and_count() for example?

> +{
> +
> +	dma_cookie_t cookie;

Above lines probably have to be exchanged.

> +	cookie = tx->tx_submit(tx);

And you may incorporate this line into above.

> +
> +	preempt_disable();
> +	__this_cpu_add(chan->local->bytes_transferred, len);
> +	__this_cpu_inc(chan->local->memcpy_count);
> +	preempt_enable();
> +
> +	return cookie;
> +

Redundant empty line.

> +}

-- 
Andy Shevchenko <andriy.shevchenko@...el.com>
Intel Finland Oy
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