linux-kernel - Re: [PATCH] PM / Domains: If an OF node is found but no device probed yet, defer.

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Message-ID: <878uetq5jk.fsf@eliezer.anholt.net>
Date:	Wed, 18 Mar 2015 15:55:43 -0700
From:	Eric Anholt <eric@...olt.net>
To:	Ulf Hansson <ulf.hansson@...aro.org>,
	Kevin Hilman <khilman@...nel.org>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] PM / Domains: If an OF node is found but no device probed yet, defer.

Ulf Hansson <ulf.hansson@...aro.org> writes:

> On 13 March 2015 at 19:01, Kevin Hilman <khilman@...nel.org> wrote:
>> Geert Uytterhoeven <geert@...ux-m68k.org> writes:
>>
>>> On Wed, Mar 11, 2015 at 11:08 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>>>> More CCes.
>>>>
>>>> On Wednesday, March 11, 2015 08:27:28 AM Eric Anholt wrote:
>>>>> If we've declared a power domain in the OF, and the OF node is found
>>>>> but the requested domain hasn't been registered on it yet, then we
>>>>> probably have just tried to probe before the power domain driver has.
>>>>> Defer our device's probe until it shows up.
>>>>>
>>>>> Signed-off-by: Eric Anholt <eric@...olt.net>
>>>>
>>>> Kevin, Ulf, any chance to have a look at this, please?
>>>>
>>>>> ---
>>>>>
>>>>> I ran into this when turning my ad-hoc code for BCM2835 (Raspberry Pi)
>>>>> USB poweron support in the DWC2 controller to an OF-based power domain
>>>>> declaration.
>>>
>>> I guess you are initializing the PM domains from module_init()?
>>>
>>> I use core_initcall() in arch/arm/mach-shmobile/pm-rmobile.c to make sure it's
>>> initialized earlier, as e.g. the interrupt controller uses postcore_initcall().
>>
>> Yeah, I think most existing users are initizling PM domains early, but IMO
>> we should be working towards supporting PM domains that are created
>> later as well (as this patch does.)
>
> I do agree, that we _should_ allow PM domains to be created later/any
> time. Unfortunate, that's not going to be a simple one-liner patch.
> :-)
>
> To have genpd_dev_pm_attach() return -EPROBE_DEFER, due to that the PM
> domain hasn’t been _initialized_ yet, we need to know whether a PM
> domain exists at all for the device. In principle we need to split the
> work done by genpd_dev_pm_attach() into the two parts described below.
>
> 1.
> At struct device creation time, done from the "OF core", we also need
> to parse for a PM domain node. If such is found, we somehow needs to
> assigned it to the device.
>
> Normally we would have assigned the struct dev_pm_domain in the struct
> device to deal with this, but that has some implications. Currently
> the struct dev_pm_domain is created from SoC specific code and it's
> also done at different init levels.

I haven't made sense of what's actually proposed here, so I'm not
stepping forward to write this.  I think I'd be less confused if the
"struct device" references in the explanation made it clear which ones
were the pm domain controller and which were the pm domain consumer.

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