Re: [PATCH 2/4] clk: renesas: mstp: Use always-on governor for Clock Domain

From: Ulf Hansson <ulf.hansson@linaro.org>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>,
	Michael Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@codeaurora.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Kevin Hilman <khilman@kernel.org>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	linux-clk <linux-clk@vger.kernel.org>,
	"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
	linux-renesas-soc@vger.kernel.org
Subject: Re: [PATCH 2/4] clk: renesas: mstp: Use always-on governor for Clock Domain
Date: Wed, 27 Apr 2016 16:07:33 +0200	[thread overview]
Message-ID: <CAPDyKFrSc8YdPc08eZ1usBOrNOkYxqY4BZnPTSk_1EDFpOWs-A@mail.gmail.com> (raw)
In-Reply-To: <CAMuHMdWyzbd8n-3+AZ16b9HL2prYQM2YXfcm8PKa_TbJ1QDQtg@mail.gmail.com>

On 27 April 2016 at 16:04, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> Hi Ulf,
>
> On Wed, Apr 27, 2016 at 3:59 PM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>> On 26 April 2016 at 09:09, Geert Uytterhoeven <geert+renesas@glider.be> wrote:
>>> As a pure Clock Domain does not have the concept of powering the domain
>>> itself, the CPG/MSTP driver does not provide power_off() and power_on()
>>> callbacks.
>>> However, the genpd core may still perform a dummy power down, causing
>>> /sys/kernel/debug/pm_genpd/pm_genpd_summary to report the domain's
>>> status being "off-0".
>>>
>>> Use the always-on governor to make sure the domain is never powered
>>> down, and always shows up as "on" in pm_genpd_summary.
>>
>> Hmm.
>>
>> Hypothetically, what if the clock domain would be a subdomain, where
>> its master is able to power down? Using the always on governor would
>> prevent the master from power off as well.
>
> That's correct. However, on R-Mobile/R-Car SoCs, this is not the case, so it
> doesn't matter here.
>
>> I am wondering whether we should introduce some similar as
>> pm_runtime_no_callbacks() but for the generic PM domain instead.
>>
>> What do you think?
>
> In my case, the domain is not managed by its parent, to there's no such
> analogy.

Ok, fair enough.

This looks good to me!

Kind regards
Uffe

>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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