linux-kernel - Re: [PATCH v9 2/3] DMA: Freescale: Add new 8-channel DMA engine device tree nodes

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Date:	Mon, 16 Sep 2013 17:46:30 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Mark Rutland <mark.rutland@....com>
CC:	Hongbo Zhang <hongbo.zhang@...escale.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"ian.campbell@...rix.com" <ian.campbell@...rix.com>,
	Pawel Moll <Pawel.Moll@....com>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	"vinod.koul@...el.com" <vinod.koul@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"djbw@...com" <djbw@...com>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v9 2/3] DMA: Freescale: Add new 8-channel DMA engine
 device tree nodes

On Thu, 2013-09-12 at 18:15 +0100, Mark Rutland wrote:
> On Tue, Sep 03, 2013 at 10:01:50AM +0100, Hongbo Zhang wrote:
> > On 09/02/2013 11:58 PM, Mark Rutland wrote:
> > > May some channels be unusable for some reason, or will all eight
> > > channels be wired on any given Elo3 DMA?
> > Sorry, not get your point clearly, maybe you are clear now because of my
> > previous explanations.
> 
> I assume that on any El03 DMA, there won't be a case where you can't
> describe the channel at 0x80, for instance. It will always be present
> (but it might not be wired up to anything any therefore be useful)?
> 
> This was related to my concerns about the status register description --
> if the channels at 0x0,0x80,0x100,0x180 weren't wired, what would get
> described in the dt? I guess that would never actually happen because
> all 8 channels must always be present in the Elo3 IP block.

If a channel is not usable for whatever reason (other than that "used
for a different fixed purpose and thus described with a different
compatible" thing that was mentioned earlier in these threads), wouldn't
it just have status = "disabled" or similar, or be absent?

-Scott



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