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

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Message-ID: <20131016053857.GV2954@intel.com>
Date:	Wed, 16 Oct 2013 11:08:57 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Youquan Song <youquan.song@...ux.jf.intel.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 08:55:20AM -0700, Dan Williams wrote:
> 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.
Well am going to take it a bit further and ask you why do we need the
/sys/class/dma? I have never used it for slave work.

Does it get used anywhere in async_tx?

--
~Vinod
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