linux-kernel - Re: [RFC PATCH 2/3] PM / Domains: Add support for devices with multiple domains

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Date:   Fri, 23 Sep 2016 16:27:41 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-tegra@...r.kernel.org,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [RFC PATCH 2/3] PM / Domains: Add support for devices with
 multiple domains

Hi Jon,

On Fri, Sep 23, 2016 at 2:57 PM, Jon Hunter <jonathanh@...dia.com> wrote:
> On 21/09/16 15:57, Geert Uytterhoeven wrote:
>> On Wed, Sep 21, 2016 at 4:37 PM, Jon Hunter <jonathanh@...dia.com> wrote:
>>> On 21/09/16 09:53, Geert Uytterhoeven wrote:
>>>> On Tue, Sep 20, 2016 at 12:28 PM, Jon Hunter <jonathanh@...dia.com> wrote:
>>>>> Some devices may require more than one PM domain to operate and this is
>>>>> not currently by the PM domain framework. Furthermore, the current Linux
>>>>> 'device' structure only allows devices to be associated with a single PM
>>>>> domain and so cannot easily be associated with more than one. To allow
>>>>> devices to be associated with more than one PM domain, if multiple
>>>>> domains are defined for a given device (eg. via device-tree), then:
>>>>> 1. Create a new PM domain for this device. The name of the new PM domain
>>>>>    created matches the device name for which it was created for.
>>>>> 2. Register the new PM domain as a sub-domain for all PM domains
>>>>>    required by the device.
>>>>> 3. Attach the device to the new PM domain.
>>>>
>>>> This looks a suboptimal to me: if you have n devices sharing the same PM
>>>> domains, you would add n new subdomains?
>>>
>>> BTW, would this be the case today for some renesas devices or are you
>>> just pointing this out as something that could be optimised/improved?
>>
>> This is the case for all Renesas SoCs that have power areas: devices belong
>> to both the PM domain for the power area, and to the PM domain for the clock
>> domain.
>
> To quantify this a bit, for the Renesas case, how many of these
> duplicated domains would there be if you were to use this approach as-is?

for i in $(git grep -l renesas, -- "*dts*") ; do echo --- $i ---; git
grep -w power-domains $i | sort | uniq -c | sort -n;done

tells you how many (supported) devices are (currently) present in each
PM domain.
Most of these (all but devices in CPU/SCU power areas) are also part of a
clock domain.
The synthetic R8A779*_PD_ALWAYS_ON domains could be dropped again,
as we could just refer to the CPG/MSSR node for the clock domain instead.

For older SH/R-Mobile SoCs with lots of hierarchical domains, that gives us,
after removing the above:

      1 arch/arm/boot/dts/r8a7740.dtsi:         power-domains = <&pd_a4mp>;
      1 arch/arm/boot/dts/r8a7740.dtsi:         power-domains = <&pd_d4>;
      2 arch/arm/boot/dts/r8a7740.dtsi:         power-domains = <&pd_c5>;
      3 arch/arm/boot/dts/r8a7740.dtsi:         power-domains = <&pd_a4r>;
      6 arch/arm/boot/dts/r8a7740.dtsi:         power-domains = <&pd_a4s>;
     15 arch/arm/boot/dts/r8a7740.dtsi:         power-domains = <&pd_a3sp>;

R-Car Gen1/Gen2 have all devices in the "always on" PM domain, so they're
not affected.

R-Car Gen3 again has devices in power areas, mostly for graphics related
purposes:

     16 arch/arm64/boot/dts/renesas/r8a7795.dtsi:
 power-domains = <&sysc R8A7795_PD_A3VP>;

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