linux-kernel - Re: [PATCH v9 14/16] iommu/exynos: add support for power management subsystems.

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Date:	Mon, 12 Aug 2013 10:55:01 +0900
From:	Cho KyongHo <pullip.cho@...sung.com>
To:	Tomasz Figa <tomasz.figa@...il.com>
Cc:	'Linux ARM Kernel' <linux-arm-kernel@...ts.infradead.org>,
	'Linux IOMMU' <iommu@...ts.linux-foundation.org>,
	'Linux Kernel' <linux-kernel@...r.kernel.org>,
	'Linux Samsung SOC' <linux-samsung-soc@...r.kernel.org>,
	devicetree@...r.kernel.org, 'Joerg Roedel' <joro@...tes.org>,
	'Kukjin Kim' <kgene.kim@...sung.com>,
	'Prathyush' <prathyush.k@...sung.com>,
	'Rahul Sharma' <rahul.sharma@...sung.com>,
	'Subash Patel' <supash.ramaswamy@...aro.org>,
	'Grant Grundler' <grundler@...omium.org>,
	'Antonios Motakis' <a.motakis@...tualopensystems.com>,
	kvmarm@...ts.cs.columbia.edu,
	'Sachin Kamat' <sachin.kamat@...aro.org>
Subject: Re: [PATCH v9 14/16] iommu/exynos: add support for power management
 subsystems.

On Fri, 09 Aug 2013 10:32:40 +0200, Tomasz Figa wrote:
> On Friday 09 of August 2013 16:49:43 Cho KyongHo wrote:
> > On Fri, 09 Aug 2013 01:03:05 +0200, Tomasz Figa wrote:
> > > Hi KyongHo,
> > > 
> > > nit: Please drop the trailing dot at the end of patch subject.
> > 
> > Oh. I didn't catch that.
> > Thank you.
> > 
> > > On Thursday 08 of August 2013 18:41:17 Cho KyongHo wrote:
> > > > This adds support for Advance Power Management and Runtime Power
> > > > Management.
> > > 
> > > This patch adds support for system-wide and runtime power management.
> > 
> > Ok.
> > 
> > > > Since System MMU is located in the same local power domain of its
> > > > master H/W, System MMU must be initialized before it is working if
> > > > its power domain was ever turned off. TLB invalidation according to
> > > > unmapping on page tables must also be performed while power domain
> > > > is
> > > > turned on.
> > > > 
> > > > This patch ensures that resume and runtime_resume(restore_state)
> > > > functions in this driver is called before the calls to resume and
> > > > runtime_resume callback functions in the drivers of master H/Ws.
> > > > Likewise, suspend and runtime_suspend(save_state) functions in this
> > > > driver is called after the calls to suspend and runtime_suspend in
> > > > the
> > > > drivers of master H/Ws.
> > > > 
> > > > In order to get benefit of this support, the master H/W and its
> > > > System
> > > > MMU must resides in the same power domain in terms of Linux kernel.
> > > > If
> > > > a master H/W does not use generic I/O power domain, its driver must
> > > > call iommu_attach_device() after its local power domain is turned
> > > > on,
> > > > iommu_detach_device before turned off.
> > > 
> > > I don't get the point of this last paragraph. What a power domain can
> > > be in other terms? Is there any other way to support power domains on
> > > Exynos than generic power domains?
> > 
> > I just addressed the case a device driver turns off local power of its
> > device without the help of generic I/O powerdomain.
> 
> Out of curiosity, do we have such cases for Exynos in mainline kernel? 
> IMHO this is what the generic PM core is for and drivers shouldn't care 
> about such low level PM details.

I don't know if there is the case and I also agree with you.

I hope that there is no case that I addressed.
I just mentioned an exceptional case.
The best way is that all device drivers of master H/W of System MMU register
their defvice in a generic i/o powerdomain.

Thank you.

KyongHo.
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