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

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Message-ID: <20131015153001.GA19236@kroah.com>
Date:	Tue, 15 Oct 2013 08:30:01 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Youquan Song <youquan.song@...ux.intel.com>
Cc:	Vinod Koul <vinod.koul@...el.com>,
	Youquan Song <youquan.song@...el.com>,
	dan.j.williams@...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 02:31:42PM -0400, Youquan Song 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:
> > > > 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.
> > > 
> > > Is that really a problem?  I have never heard anyone complaining about
> > > it.  Where are the reports of this?
> > Right, am not still getting the point on what is the problem that this series is
> > trying to fix..
> 
> 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.

If you are worried about the data transferred through a UART, then look
at the accounting variables for that device (in /proc/ ) and use them,
they should be a good enough hint to see that data is flowing, not the
dma data.

And again, I can't take this due to the security implications, we
already went down this path with the TTY bytes, why do you want us to
introduce the same issue again only to have to fix it again?

greg k-h
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