linux-kernel - Re: [PATCH v3 2/3] powerpc/512x: add a device tree binding for LocalPlus Bus FIFO

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Message-ID: <560A3141.6090705@linux.com>
Date:	Tue, 29 Sep 2015 09:35:45 +0300
From:	Alexander Popov <alex.popov@...ux.com>
To:	Timur Tabi <timur@...i.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Anatolij Gustschin <agust@...x.de>,
	Gerhard Sittig <gsi@...x.de>, Rob Herring <robh@...nel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	linuxppc-dev@...ts.ozlabs.org, dmaengine@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Alexander Popov <alex.popov@...ux.com>
Subject: Re: [PATCH v3 2/3] powerpc/512x: add a device tree binding for
 LocalPlus Bus FIFO

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
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