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

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Date:	Wed, 16 Oct 2013 13:27:02 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	"Shevchenko, Andriy" <andriy.shevchenko@...el.com>
Cc:	"Williams, Dan J" <dan.j.williams@...el.com>,
	Youquan Song <youquan.song@...ux.jf.intel.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	"Song, Youquan" <youquan.song@...el.com>,
	"Westerberg, Mika" <mika.westerberg@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] dma: Add interface to calculate data transferred

On Wed, Oct 16, 2013 at 02:06:30PM +0530, Shevchenko, Andriy wrote:
> On Wed, 2013-10-16 at 11:08 +0530, Vinod Koul wrote:
> > 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.
> 
> How user (who, f.e., would like to run dmatest) will know names of the
> channels provided?
Ok dmatest requires this, I overlooked that part

> How could we see what channels of certain dma controller are requested /
> busy from userspace?
But do end user care or need to know about this?

--
~Vinod
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