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Reply-To: alex.popov@linux.com
Subject: Re: [PATCH v3 2/3] powerpc/512x: add a device tree binding for
 LocalPlus Bus FIFO
References: <1443115737-3948-1-git-send-email-alex.popov@linux.com>
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 <5609401F.3010603@tabi.org>
To: Timur Tabi <timur@tabi.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Anatolij Gustschin <agust@denx.de>, Gerhard Sittig <gsi@denx.de>,
        Rob Herring <robh@kernel.org>, Grant Likely <grant.likely@linaro.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Vinod Koul <vinod.koul@intel.com>, Pawel Moll <pawel.moll@arm.com>,
        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, Alexander Popov <alex.popov@linux.com>
From: Alexander Popov <alex.popov@linux.com>
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Date: Tue, 29 Sep 2015 09:35:45 +0300
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On 28.09.2015 16:26, Timur Tabi wrote:
> 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?

No, mpc512x_lpbfifo.c is the only piece of code which is going to use 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,

Yes.
MPC512x LocalPlus Bus FIFO uses the channel #26 of the DMA controller
both for reading and writing, and other DMA clients use other specific
DMA channels. This channel assignment is fixed in hardware and described
in the Reference Manual.

> but it is a required property.
> I guess you should keep it, but I think you should get a second opinion.

Ok, thanks.

Best regards,
Alexander