linux-kernel - Re: [PATCH/RFC 3/4] of/clk: Register clocks suitable for Runtime PM with the PM core

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Date:	Fri, 2 May 2014 16:58:03 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	Tomasz Figa <tomasz.figa@...il.com>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Magnus Damm <magnus.damm@...il.com>,
	Simon Horman <horms@...ge.net.au>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	Felipe Balbi <balbi@...com>,
	Mike Turquette <mturquette@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-omap <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH/RFC 3/4] of/clk: Register clocks suitable for Runtime PM
 with the PM core

Hi Ulf, Tomasz,

On Fri, May 2, 2014 at 10:13 AM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>>>> +static int of_clk_register(struct device *dev, struct clk *clk)
>>>> +{
>>>> +       int error;
>>>> +
>>>> +       if (!dev->pm_domain) {
>>>> +               error = pm_clk_create(dev);
>>>> +               if (error)
>>>> +                       return error;
>>>> +
>>>> +               dev->pm_domain = &of_clk_pm_domain;
>>>
>>>
>>> I am concerned about how this will work in conjunction with the
>>> generic power domain.
>>>
>>> A device can't reside in more than one pm_domain; thus I think it
>>> would be better to always use the generic power domain and not have a
>>> specific one for clocks. Typically the genpd should invoke
>>> pm_clk_resume|suspend from it's runtime PM callbacks.
>>
>> I'm not sure about this. A typical use case would be to gate clocks ASAP and
>> then wait until device is idle long enough to consider turning off the power
>> domain worthwhile. Also sometimes we may want to gate the clocks, but
>> prevent power domain from being powered off to retain hardware state (e.g.
>> because there is no way to read it and restore later).
>
> So, in principle you prefer to have driver's handle clock gating to
> save power from their runtime PM callbacks, instead of from the power
> domain, right? Just to clarify, that's my view as well.

If there's both a gate clock and a power domain, and the driver's Runtime PM
callbacks handle clock gating, who's handling the power domain?

Gr{oetje,eeting}s,

                        Geert (still trying to fit all pieces of the
puzzle together)

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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