linux-kernel - Re: [PATCH RFC v3 1/2] PM / Domains: Extend API pm_genpd_dev_need

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Date:	Thu, 18 Dec 2014 11:05:18 +0100
From:	Sylwester Nawrocki <s.nawrocki@...sung.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Kevin Hilman <khilman@...nel.org>
Cc:	amit daniel kachhap <amit.daniel@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	LAK <linux-arm-kernel@...ts.infradead.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Len Brown <len.brown@...el.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Thomas Abraham <thomas.ab@...sung.com>,
	Pankaj Dubey <pankaj.dubey@...sung.com>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v3 1/2] PM / Domains: Extend API
 pm_genpd_dev_need_restore to use restore types

On 18/12/14 01:58, Rafael J. Wysocki wrote:
>>>> What's needed to solve this problem is a generalized way to have runtime
>>>> > >> PM dependencies between devices.  Runtime PM already automatically
>>>> > >> handles parent devices as one type of dependent device (e.g. a parent
>>>> > >> device needs to be runtime PM resumed before its child.)  So what's
>>>> > >> needed is a generic way to other PM dependencies with the runtime PM
>>>> > >> core (not the genpd core.)
>>> > >
>>> > > Considering the example above with three devices, device D1 and D2 are
>>> > > passive components in this power domain. These devices only need to
>>> > > know the state changes of the power domains but would not control the
>>> > > power domain themselves nor put forth constraints in the power domain
>>> > > state changes. So I did not clearly understand as to how this example
>>> > > could be solved by introducing changes in runtime PM core.
>> > 
>> > Your solution only solves the problems for devices managed by genpd.
>> > 
>> > If I understood your example correctly, what you really want to solve
>> > this problem more generically is to be able to tell the runtime PM core
>> > that D3 has a dependency on D1 and D2.  Then, whenver the runtime PM
>> > core is doing get/put operations for D3, it needs to also do them for D1
>> > and D2.

Indeed, I think it would solve most of the problems if we were able to
model the PM dependencies between devices which would then be handled
in the PM core.  I recall something like this has been proposed a while
ago [1].

>> > This will accomplish the same as your proposed approach, but work for
>> > any devices in any PM domains.
>
> Plus, it is not limited to runtime PM, really.  It affects system suspend
> too.

[1] https://lkml.org/lkml/2009/8/26/485

-- 
Regards,
Sylwester
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