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Subject: Re: [PATCH v3 2/3] powerpc/512x: add a device tree binding for
 LocalPlus Bus FIFO
To: alex.popov@linux.com, Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
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        Mark Rutland <mark.rutland@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Kumar Gala <galak@codeaurora.org>, linuxppc-dev@lists.ozlabs.org,
        dmaengine@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
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From: Timur Tabi <timur@tabi.org>
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Date: Mon, 28 Sep 2015 08:26:55 -0500
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Alexander Popov wrote:
> I've just followed devicetree/bindings/dma/dma.txt...
> This "rx-tx" doesn't mean much but it could show that LocalPlus Bus FIFO
> uses a single DMA read-write channel. Should I really drop it?

Hmmm, I'm not sure.  Is there anything else (besides your driver) that 
parses this device tree node?

dma.txt says this:

	"The specific strings that can be used are defined in the binding of 
the DMA client device."

So this looks like it's driver-specific, but it is a required property.
I guess you should keep it, but I think you should get a second opinion.