linux-kernel - Re: [PATCH v4 1/2] ARM: keystone: pm: switch to use generic pm domains

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Message-ID: <546DD87B.3080806@ti.com>
Date:	Thu, 20 Nov 2014 14:03:07 +0200
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Ulf Hansson <ulf.hansson@...aro.org>, Arnd Bergmann <arnd@...db.de>
CC:	Kevin Hilman <khilman@...nel.org>, <ssantosh@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: [PATCH v4 1/2] ARM: keystone: pm: switch to use generic pm domains

On 11/20/2014 01:34 PM, Ulf Hansson wrote:
> On 19 November 2014 14:47, Arnd Bergmann <arnd@...db.de> wrote:
>> On Wednesday 19 November 2014 13:32:45 Grygorii Strashko wrote:
>>> On 11/18/2014 09:32 PM, Arnd Bergmann wrote:
>>>> On Tuesday 18 November 2014 20:54:36 Grygorii Strashko wrote:
>>>>
>>>> Have one pmdomain driver in the generic code that knows about clocks,
>>>> possibly also regulators and pins and just turns them on when needed.
>>>> You can have a "simple-pmdomain" or "generic-pmdomain" compatible
>>>> string.
>>>>
>>>> I'm a bit surprised that your pmdomain code looks up the clocks from the
>>>> respective device, rather than know about the clocks itself. There is
>>>> probably a good reason for this, but I don't see it yet.
>>>
>>> The keystone 2 uses simple PM schema based on clocks only:
>>> - clocks enabled -> dev is active
>>> - clocks disabled -> dev is suspended
>>>
>>> To achieve explained above the Generic clock manipulation PM callbacks framework (pm_clk) is used.
>>> - list of managed clocks is filled for each device (for non-DT case the con_id list
>>>    is specified by platform code like:
>>>        .con_ids = { "fck", "master", "slave", NULL },
>>>          - or -
>>>        .con_ids = { }, <-- in this case only first clock will be added to pm_clk
>>>    )
> 
> According to earlier comments in this thread, device's clocks are
> split into "functional" and "PM" clocks.
> 
> If I understand correctly, a typical platform driver will enable it's
> "functional" clocks during ->probe() and you want the PM domain to
> take care of the "PM" clocks, when the device changes runtime PM
> status.
> 
> How will you describe these different set of device clocks in DT?

True :(  You can dig deeper in the history of this series if you wish.
- first Geert Uytterhoeven proposed to use CLK_RUNTIME_PM there 
  https://lkml.org/lkml/2014/11/6/319
- second I proposed to introduce smth. like "clkops-clocks", "pm-clocks" there
  https://lkml.org/lkml/2014/6/12/436
 or "fck-clocks"/"opt-clocks" later. 

^failed.

So, this implementation picks up all clocks for each device, which is ok for
Keystone 2 and, because it's platform specific.

>>
>> Yes, it would definitely solve the problem that I see with the infrastructure
>> code that the current version adds into the platform directory.
>>
>> The exact binding of course should be reviewed by the pmdomain and
>> DT maintainers, to ensure that it is done the best possible way, because
>> I assume we will end up using it a lot, and it would be a shame to get
>> it slightly wrong.
>>
>> One possible variation I can think of would be to just use "simple-pmdomain"
>> as the compatible string, and use properties in the node itself to decide
>> what the domain should control, e.g.
>>
>>          clk_pmdomain: pmdomain {
>>                  compatible = "simple-pmdomain";
>>                  pmdomain-enable-clocks;
>>                  #power-domain-cells = <0>;
>>          };
>>          clk_regulator_pmdomain: pmdomain {
>>                  compatible = "simple-pmdomain";
>>                  pmdomain-enable-clocks;
>>                  pmdomain-enable-regulators;
>>                  #power-domain-cells = <0>;
>>          };
>>
>> and then have each device link to one of the nodes as the pmdomain.
>>
> 
> That's seems like a good approach to me.
 
Yes, but your previous comment is still actual :(

Regards,
-grygorii
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