linux-kernel - Re: [PATCH v11 17/27] iommu/exynos: remove calls to Runtime PM API functions

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Message-ID: <CANEJEGuYz28dGT+264CYtG+Tk6htOq=u-t4PWMtsij32X0vJFA@mail.gmail.com>
Date:	Wed, 19 Mar 2014 10:03:33 -0700
From:	Grant Grundler <grundler@...omium.org>
To:	Tomasz Figa <t.figa@...sung.com>
Cc:	Cho KyongHo <pullip.cho@...sung.com>,
	Linux ARM Kernel <linux-arm-kernel@...ts.infradead.org>,
	Linux DeviceTree <devicetree@...r.kernel.org>,
	Linux IOMMU <iommu@...ts.linux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Samsung SOC <linux-samsung-soc@...r.kernel.org>,
	Antonios Motakis <a.motakis@...tualopensystems.com>,
	Grant Grundler <grundler@...omium.org>,
	Joerg Roedel <joro@...tes.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Prathyush <prathyush.k@...sung.com>,
	Rahul Sharma <rahul.sharma@...sung.com>,
	Sachin Kamat <sachin.kamat@...aro.org>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Varun Sethi <Varun.Sethi@...escale.com>
Subject: Re: [PATCH v11 17/27] iommu/exynos: remove calls to Runtime PM API functions

On Wed, Mar 19, 2014 at 6:12 AM, Tomasz Figa <t.figa@...sung.com> wrote:
...
> No. Proper Linux drivers must support deferred probing mechanism and there
> should be no assumptions about probing orders. Using other initcall level
> than module_initcall for particular drivers is strongly discouraged.

That's true for "end-point" devices. It's not true for
"infrastructure": Memory, CPU, DMA, Interrupt handling, etc. Those
need to be in place before "normal" drivers get called. This SysMMU
driver provides DMA services for "normal" device drivers. Or do I see
that wrong?

thanks,
grant

ps. I've written IOMMU support for four different IOMMUs on three
operating systems (See drivers/parisc for two linux examples). But I
still feel like I at best have 80% understanding of how this one is
organized/works. Abstract descriptions and convoluted code have been
handicapping me (and lack of time to dig further).
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