linux-kernel - Re: [PATCH v12 11/31] documentation: iommu: add binding document of Exynos System MMU

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Message-ID: <535E9558.8010803@wwwdotorg.org>
Date:	Mon, 28 Apr 2014 11:52:24 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Thierry Reding <thierry.reding@...il.com>,
	Arnd Bergmann <arnd@...db.de>
CC:	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	kgene.kim@...sung.com, Shaik Ameer Basha <shaik.ameer@...sung.com>,
	prathyush.k@...sung.com, grundler@...omium.org, joro@...tes.org,
	supash.ramaswamy@...aro.org, linux-kernel@...r.kernel.org,
	pullip.cho@...sung.com, tomasz.figa@...il.com,
	sachin.kamat@...aro.org, iommu@...ts.linux-foundation.org,
	linux-samsung-soc@...r.kernel.org, s.nawrocki@...sung.com,
	a.motakis@...tualopensystems.com, Varun.Sethi@...escale.com,
	joshi@...sung.com, t.figa@...sung.com, rahul.sharma@...sung.com,
	Hiroshi Doyu <hdoyu@...dia.com>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v12 11/31] documentation: iommu: add binding document
 of Exynos System MMU

On 04/28/2014 05:18 AM, Thierry Reding wrote:
> On Mon, Apr 28, 2014 at 12:56:03PM +0200, Arnd Bergmann wrote:
...
>> A lot of drivers probably only support one
>> master, so they can just set #iommu-cells=<0>, others might require
>> IDs that do not fit into one cell.
> 
> You mean "#iommu-cells = <1>" for devices that only require one master?
> There still has to be one cell to specify which master. Unless perhaps
> if they can be arbitrarily assigned. I guess even if there's a fixed
> mapping that applies to one SoC generation, it might be good to still
> employ a specifier and have the mapping in DT for flexibility.

#iommu-cells doesn't include the phandle, so if you want the client
references to be:

property = <&iommu>;

then that's #iommu-cells=<0>, whereas:

property = <&iommu N>;

is #iommu-cells=<1>.


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