linux-kernel - Re: [PATCH RFC RFT 3/3] clk: introduce CLK_ENABLE_HAND

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Message-ID: <CAMuHMdX0cpus6hY2ZXJiJbpe8TQsd4WZ7XTTGR_4WfH-cy_DNA@mail.gmail.com>
Date:	Tue, 11 Aug 2015 14:34:59 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Maxime Coquelin <maxime.coquelin@...com>
Cc:	Lee Jones <lee.jones@...aro.org>,
	Michael Turquette <mturquette@...libre.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-clk@...r.kernel.org, Stephen Boyd <sboyd@...eaurora.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Sascha Hauer <s.hauer@...gutronix.de>
Subject: Re: [PATCH RFC RFT 3/3] clk: introduce CLK_ENABLE_HAND_OFF flag

On Tue, Aug 11, 2015 at 2:03 PM, Maxime Coquelin <maxime.coquelin@...com> wrote:
> On 08/11/2015 01:49 PM, Geert Uytterhoeven wrote:
>> On Tue, Aug 11, 2015 at 1:41 PM, Maxime Coquelin <maxime.coquelin@...com>
>> wrote:
>>> On 08/11/2015 01:36 PM, Maxime Coquelin wrote:
>>>> On 08/11/2015 12:11 PM, Geert Uytterhoeven wrote:
>>>>> On Tue, Aug 11, 2015 at 12:02 PM, Maxime Coquelin
>>>>> <maxime.coquelin@...com> wrote:
>>>>>> How can we pass CLK_ENABLE_HAND_OFF flag to a specific clock on STi
>>>>>> platform?
>>>>>
>>>>> Add the flag to the relevant clocks in the C code, e.g. in
>>>>> clk_register_flexgen():
>>>>>
>>>>>           if (!strcmp(name, "clk-icn-cpu"))
>>>>>                   init.flags |= CLK_ENABLE_HAND_OFF;
>>>
>>> The main problem I see with this proposal is that clk_register_flexgen()
>>> is
>>> called for several SoCs (STiH407/410/418...).
>>> Each of these SoCs have this clock, but maybe STiH407 will need the flag,
>>> but not STiH410 and STiH418.
>>> So I think the best place to set this information is in DT, where the
>>> differentiation is made between the SoCs.
>>
>> If (of_machine_is_compatible("st,stih410")) ...
>>
> It works, but is it really what we want?
> Each time we will add a new soc, we will have to patch this SoC agnostic
> function?
> With the number of SoCs and the number of clocks, it will be a nightmare to
> maintain and debug, no?

One day[*], when you will discover the presence of the small security-related
control processor, you will finally understand why it can disable and enable
e.g. your main CPU clock, and may want to write a driver for it. Then you can
just remove the CLK_ENABLE_HAND_OFF flags.

[*] Perhaps this day has already happened, but obviously you're not allowed
    to discuss this on a public mailing list ;-)

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
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