linux-kernel - Re: [PATCH] dma: Add Xilinx AXI Video Direct Memory Access Engine driver support

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Message-Id: <201401201941.07633.arnd@arndb.de>
Date:	Mon, 20 Jan 2014 19:41:07 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Srikanth Thokala <sthokal@...inx.com>
Cc:	linux-arm-kernel@...ts.infradead.org, dan.j.williams@...el.com,
	vinod.koul@...el.com, michal.simek@...inx.com,
	Grant Likely <grant.likely@...aro.org>, robh+dt@...nel.org,
	dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma: Add Xilinx AXI Video Direct Memory Access Engine driver support

On Monday 20 January 2014, Srikanth Thokala wrote:
> >
> >> > * data width should be a property of the slave driver that is configured
> >> >   through dma_slave_config(), unless you can have dma engines that only
> >> >   support certain a width.
> >>
> >> Yes, this VDMA engine soft IP support only certain widths, which is
> >> configurable during IP synthesis.
> >
> > But what is this property used for in that case? Surely you can't
> > connect a slave device to a dmaengine if the bus width doesn't match.
> > You probably have a point here, but I don't understand it yet.
> 
> There is a Data-Realignment Engine (DRE) in the IP which is only available for
> data width setting of 64-bits and less.  So, we use the data-width DT parameter
> to verify this condition and we update alignment shift accordingly.

Ok, I have to admit I didn't understand all of that, but you clearly
know what you are talking about here, so I assume you are correct.

	Arnd
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