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

From: Grygorii Strashko
Date: Tue Nov 18 2014 - 13:55:31 EST

Hi All,

Thank you for your comments.

On 11/17/2014 11:50 PM, Kevin Hilman wrote:
> Arnd Bergmann <arnd@xxxxxxxx> 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,

Hm. I've been thinking about this, but the problem is that Keystone 2
reuses a lot of IPs from Davinci and PM for Davinci is based on Generic clock
manipulation PM callbacks framework, but for non-DT case. So, I can't simply
use 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'd like to mention few points here:
1) not all platforms may need this

2) not all platforms may allow to add ALL clocks from "clocks" property
to pm_clk as some of them can be optional or have to be controlled by drivers only
(for example, initially, it was the case for SH-mobile
also now, last implementation for shmobile add only first clock from "clocks" property
to pm_clk

3) such functionality have to be enabled for devices selectively, for example
now we are going to enable it for devices which a ready for runtime PM.

Current implementation cover 1 & 3, but also it allows to cover 2 too, because
it's platform specific implementation and .attach_dev() can be updated to skip some
clocks or devices if needed.

> 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.

I'm ready to do what ever you want, but I don't fully understand what exactly to do :(
Should I create some generic_pm_clk_domain.c?
- or - Do you mean to integrate it in domain.c (see no way to do it:()?
- or - smth. else

What about introduced DT bindings? For example, How will devices be selected for attachment
to Generic pm_clk domain if I'll introduce generic_pm_clk_domain.c?

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