linux-kernel - Re: [PATCH v2 0/3] ARM: rk3288 : Add PM Domain support

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Date:	Wed, 01 Oct 2014 13:25:06 -0700
From:	Kevin Hilman <khilman@...nel.org>
To:	Doug Anderson <dianders@...omium.org>
Cc:	"jinkun.hong" <jinkun.hong@...k-chips.com>,
	Russell King <linux@....linux.org.uk>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree\@vger.kernel.org" <devicetree@...r.kernel.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	"linux-doc\@vger.kernel.org" <linux-doc@...r.kernel.org>,
	Heiko Stuebner <heiko@...ech.de>,
	linux-rockchip@...ts.infradead.org,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: [PATCH v2 0/3] ARM: rk3288 : Add PM Domain support

Doug Anderson <dianders@...omium.org> writes:

> Kevin,
>
> On Wed, Oct 1, 2014 at 9:51 AM, Kevin Hilman <khilman@...nel.org> wrote:
>> +Geert, Ulf
>>
>> "jinkun.hong" <jinkun.hong@...k-chips.com> writes:
>>
>>> From: "jinkun.hong" <jinkun.hong@...k-chips.com>
>>>
>>> Use PM Domain framework to manage the clock.
>>
>> Which clock?  This changelog needs a more thorough description.
>
>
> I think what he meant was:
>
> Use the generic PM Domain framework for Rockchip
>
> ...but I agree that he could describe it more.
>
>
>> Also,
>> with this series alone, it's not clear how the power-domain transitions
>> ever happen, since I don't see any devices hooked up to your power
>> domains, or do I see your platform using runtime PM.  In order for this
>> to be reviewed properely, it's important for reviewers to be able to see
>> how this PM domain support will be used.
>
> I noticed that too.  As the patchset currently stands it only ever disables...
>
>
>> Also, remember that the DT is supposed to reflect the hardware, not the
>> design choices of linux drivers.  Because of that, it's a little
>> surprising to see clocks as properties of a power domain because clocks
>> are usually properties of devices.
>
> I haven't dug all the way into the hardware to figure out why (or if
> this is really necessary), but right now the rockchip power domain
> driver only leaves these clocks on during the powering on and powering
> off of the power domain.  In other words to turn on the power domain:
>
> 1. Turn on all clocks
> 2. Flip the bit that sets the power domain on
> 3. Wait until hardware says power domain is on.
> 4. Turn off all the clocks.
>
> ...and to turn off:
>
> 1. Turn on all clocks
> 2. Flip the bit that sets the power domain off
> 3. Wait until hardware says power domain is off.
> 2. Turn off all the clocks.
>
> ...if the above is actually necessary when turning on and off power
> domains then it seems like it is actually describing the hardware.

Yes, I understand. The need to have some *device* clocks enabled when
powering on/off the power-domain itself is quite common across many
SoCs.

My point is that these clocks are actually properties of *devices*, not
the power-domain itself.  In the shmobile example I pointed to, the
clocks are properties of the devices in DT, and the devices are attached
to the powerdomain.  When the devices are connected to the power-domain,
the custom attach function looks up all the *device* clocks and and
addes them to the power-domain using pm_clk_add.

Since the clocks are properties of devices, then the pm_clk
infrastructure can be used (as the shmobile example shows) so that the
SoC specific pm-domain doesn't have to manually walk all the clocks, but
instead can just use pm_clk_suspend/pm_clk_resume.

Kevin






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