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

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Message-ID: <7hsihhzecq.fsf@deeprootsystems.com>
Date:	Mon, 17 Nov 2014 13:50:13 -0800
From:	Kevin Hilman <khilman@...nel.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Grygorii Strashko <grygorii.strashko@...com>, ssantosh@...nel.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
	Rob Herring <robh+dt@...nel.org>, grant.likely@...retlab.ca,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, Ulf Hansson <ulf.hansson@...aro.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

Arnd Bergmann <arnd@...db.de> writes:

> On Monday 17 November 2014 11:14:16 Kevin Hilman wrote:
>> >> 
>> >> So, The Keystone 2 Generic PM Controller is just a proxy PM layer here between
>> >> device and Generic clock manipulation PM callbacks.
>> >> It fills per-device clock list when device is attached to GPD and
>> >> ensures that all clocks from that list enabled/disabled when device is
>> >> started/stopped.
>> >
>> > The idea of such a generic power domain implementation sounds useful, but
>> > it has absolutely no business in platform specific code.
>> 
>> Yes it does.  This isn't a generic power domain implementation, but
>> rather just the platform-specific glue that hooks up the clocks to the
>> right devices and power-domains so that the generic power-domain and
>> generic pm_clocks code does the right thing.
>
> How would you do this on an arm64 version of keystone then? With
> the current approach, you'd need to add a machine specific directory,
> and that seems completely pointless since this is not even about
> a hardware requirement.

Yeah, you're right.  I misunderstood you're original comment.

>> > I suggest you either remove the power domain proxy from your drivers
>> > and use the clocks directly, 
>> 
>> No.  That's a step in the wrong direction.  This change isn't affecting
>> drivers directly.  It's the runtime PM and generic power domain layers
>> that handle this, and runtime PM adapted drivers don't need any changes.
>>  
>> > or come up with an implementation that can be used across other
>> > platforms and CPU architectures.
>> 
>> We already have those in the generic power domain and the pm_clock
>> layers.  This series is just hooking those up for Keystone.
>
> Then why not add the missing piece to the generic power domain
> code to avoid having to add infrastructure to the platform
> for it?

Yes, good point.  There is nothing keystone-specific in this glue.

Grygorii, what about adding a feature to the generic domain parsing so
that it can get clocks from device nodes that are part of the domain,
and so it sets up pm_clk accordingly.

I've recently seen other SoCs doing very similar, so this really should
be generalized.

I've been looking at this primarily as a right incremental improvement
from what is there for Keystone today, but Arnd is right.  This should
be moved out of platform code.

Kevin
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