linux-kernel - Re: [PATCH/RFC 0/4] Probe deferral for IOMMU DT integration

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Message-ID: <54D9265E.1030403@codeaurora.org>
Date:	Mon, 09 Feb 2015 13:27:58 -0800
From:	Laura Abbott <lauraa@...eaurora.org>
To:	"arnd@...db.de" <arnd@...db.de>, Will Deacon <will.deacon@....com>,
	Robin Murphy <robin.murphy@....com>
CC:	devicetree@...r.kernel.org,
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	Joreg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org,
	iommu@...ts.linux-foundation.org,
	Grant Likely <grant.likely@...aro.org>,
	Mitchel Humpherys <mitchelh@...eaurora.org>,
	linux-arm-kernel@...ts.infradead.org,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH/RFC 0/4] Probe deferral for IOMMU DT integration

On 2/7/2015 2:41 PM, arnd@...db.de wrote:
> Laura Abbott <lauraa@...eaurora.org> hat am 6. Februar 2015 um 01:31
> geschrieben:
>>
>> The requirement for this is based on a previous patch to add clock
>> support to the ARM SMMU driver[2]. Once we have clock support, it's
>> possible that the driver itself may need to be defered which breaks
>> a bunch of assumptions about how SMMU probing is supposed to work.
>
> Hi Laura,
>
> I was hoping that we would not need this, and instead treat the iommu in
> the same way as timers and SMP initialization, both
> of which need to be run early at boot time but may rely on clock controllers
> to be initialized first.
>
> Is there a specific requirement that makes this impossible here, or is your
> intention to solve the problem more nicely by allowing deferred probing
> over forcing the input clocks of the iommu to be early?
>
>        Arnd
>

The current clock driver for qcom targets doesn't support the early
initialization needed for timers and SMP because neither of those depend
on the clocksources. I discussed this with Stephen some and adding the
early support would not mesh well with the device/driver design of the
current clock driver so that's not really an option right now.

I do think the deferred probing design is cleaner. Even cleaner would
be a proper bus type but that's a different can of worms.

Thanks,
Laura

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