linux-kernel - Re: [RFC 2/4] driver core: Allow early registration of devices

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Message-ID: <5212757F.2080107@wwwdotorg.org>
Date:	Mon, 19 Aug 2013 13:43:59 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Thierry Reding <thierry.reding@...il.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Hiroshi Doyu <hdoyu@...dia.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/4] driver core: Allow early registration of devices

On 08/17/2013 05:17 AM, Thierry Reding wrote:
...
> Well, the most obvious cases where early initialization is needed
> are interrupt controllers and clocks.

... and IOMMUs, which apparently need to initialize before any devices
whose transactions are routed through the IOMMU, in order to set
themselves up as the IOMMU for the relevant devices.

It's possible that the CPU-visible bus structure isn't a strict
inverse/reverse of the device-visible bus-structure. A device may have
CPU-visible registers on one bus segment, but inject master
transactions onto an unrelated bus segment. So it may not be as simple
as making a bus driver for the bus segment affected by the IOMMU, and
having that driver trigger instantiation of all its children.
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