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

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Message-ID: <CAPcyv4jJSgM7EmDMW-rcjVCnC6-95+qeU9yf+yxD-wMCcQ8amg@mail.gmail.com>
Date:	Tue, 15 Oct 2013 08:55:20 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Youquan Song <youquan.song@...ux.intel.com>
Cc:	Vinod Koul <vinod.koul@...el.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Youquan Song <youquan.song@...el.com>,
	andriy.shevchenko@...el.com, mika.westerberg@...el.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dma: Add interface to calculate data transferred

On Tue, Oct 15, 2013 at 11:31 AM, Youquan Song
<youquan.song@...ux.intel.com> wrote:
> On Sun, Oct 13, 2013 at 08:56:33PM +0530, Vinod Koul wrote:
>> On Fri, Oct 11, 2013 at 06:33:43AM -0700, Greg KH wrote:
>> > On Fri, Oct 11, 2013 at 05:42:17PM -0400, Youquan Song wrote:
> The issue is that when I using UART to transfer data between to COMs
> which using Designware DMA controller channel. But I check the specific
> DMA channel by "cat /sys/class/dma/dma0chan3/bytes_transferred", but it
> should all "0". I have transferred data by UART port, why its DMA
> channel report "0" bytes transferred?  So I guess that it is possible
> the DMA device driver issue or the data does not use the Designware DMA channel
> fro transferred.  After check the code, I notice only when the DMA
> channel used by network device driver and it will record how much data has been
>  tranferred, why other device driver will not calculate it. Since DMA
> channel is used by other device driver, why only network is specific?  since it is
> common interface, the current /sys/class/dma/dma0chan*/bytes_transferred has
> much possibility to mislead the user.

Yes, and for that reason I think we should delete "
/sys/class/dma/dma0chan*/bytes_transferred" it really serves no useful
purpose besides "is my dma channel working" which can be determined by
other means.

--
Dan
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