linux-kernel - Re: [RFC PATCH 0/4] PM / Domains: Add support for explicit control of PM domains

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Message-ID: <CAMuHMdV74WvP0UcXWKEjnmkzC8f9WV+8wmwZK56jU88NY76qQQ@mail.gmail.com>
Date:   Wed, 3 May 2017 10:54:33 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Jon Hunter <jonathanh@...dia.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [RFC PATCH 0/4] PM / Domains: Add support for explicit control of
 PM domains

Hi Ulf,

On Wed, May 3, 2017 at 8:43 AM, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> On Wed, Apr 26, 2017 at 11:55 AM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>> On 26 April 2017 at 11:17, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>>> On Wed, Apr 26, 2017 at 11:04 AM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>>>> On 26 April 2017 at 10:06, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>>>>> On Tue, Apr 25, 2017 at 9:34 PM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>>>>>> However, we currently know about at least two different SoCs that need
>>>>>> this. Perhaps we can extend the below list to justify adding a new
>>>>>> framework/APIs. Something along the lines what you propose in $subject
>>>>>> patchset.
>>>>>>
>>>>>> 1) Nvidia; to solve the USB super-speed host/device problem.
>>>>>> 2) QCOM, which has pointed to several cases where the PM topology is
>>>>>> laid out like devices having two PM domains..
>>>>>> 3?) I don't fully remember - but I think Geert also pointed to some
>>>>>> examples where a device could reside in a clock domain but also in
>>>>>> power domain for a Renesas SoC!?
>>>>>> 4) ?
>>>>>
>>>>> Most Renesas SoCs have module clocks, which we model as a clock domain.
>>>>> Some Renesas SoCs have power domains for CPUs, others have them for
>>>>> devices as well.
>>>>> As we always provide a virtual "always-on" power domain in the power domain
>>>>> controller, all devices can refer to it using "power-domains" properties,
>>>>> and the driver for the power domain controller can just forward the clock
>>>>> domain operations to the clock driver.
>>>>
>>>> Okay, thanks for clarifying this.
>>>>
>>>> Thinking about this as bit more, when I realized that *if* we would
>>>> add a new PM domain framework for explicit control of PM domains, that
>>>> would mean you need to deploy support for that in the drivers.
>>>
>>> Correct.  And we have to update DT bindings and DTS.
>>>
>>>> On the other hand, as you anyway would need to change the drivers, you
>>>> could instead deploy clock support in the drivers, which would avoid
>>>> using the clock domain. In that way, you could still stay with one PM
>>>> domain pointer per device, used to control the power domains instead.
>>>> Right? Or would that have other implications?
>>>
>>> That's exactly what we're doing already.
>>
>> No really, but perhaps I was not clear enough.
>>
>> Currently you deploy only runtime PM support in the driver and don't
>> do any clk_get() etc. Then you have a PM domain (genpd) attached to

Note that drivers that care about clock properties do use clk_get().
E.g. an SPI controller driver needs to know the clock rate to program
its internal divider to drive external SPI slaves.

>> the device and makes use of genpd's device specific callbacks, in
>> struct gpd_dev_ops ->start|stop(), which allows you to control clocks
>> for each device. Of course this is perfectly okay.
>
> OK.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds