linux-kernel - Re: [PATCHv5 2/9] driver/core: populate devices in order for IOMMUs

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Message-ID: <20131125173900.GB28201@mudshark.cambridge.arm.com>
Date:	Mon, 25 Nov 2013 17:39:00 +0000
From:	Will Deacon <will.deacon@....com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Hiroshi Doyu <hdoyu@...dia.com>,
	"swarren@...dia.com" <swarren@...dia.com>,
	"thierry.reding@...il.com" <thierry.reding@...il.com>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	Mark Rutland <Mark.Rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	dave.martin@....com
Subject: Re: [PATCHv5 2/9] driver/core: populate devices in order for IOMMUs

On Fri, Nov 22, 2013 at 05:35:58PM +0000, Stephen Warren wrote:
> On 11/22/2013 12:41 AM, Grant Likely wrote:
> > It seems more that IOMMU attachment is closer to being a property of the
> > bus rather than a property of the device itself. In that context it
> > would make more sense for the bus device to hold off child device
> > registration or probing until the IOMMU is available. That keeps the
> > logic out of both the core code and the individual device drivers.
> 
> The bus structure that DT and Linux know about is the register bus.
> There's no reason that devices have to emit their master transactions
> onto that same bus, or onto only that same bus.

Agreed. Dave (CC'd) and I actually had a lot of discussion around the DT bus
abstractions last week and we ended up with a binding that looked sane enough
to start a meaningful discussion in this area.

Dave -- care to post what we came up with? It certainly has a bunch of
overlap with the IOMMU problems being discussed here.

Will
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