linux-kernel - Re: [PATCH] ARM64: Kconfig: Fix the missing hi655x common clk

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Message-ID: <3df69681-202b-1426-0a35-de943bc14ed1@linaro.org>
Date:   Tue, 13 Jun 2017 14:48:53 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     John Stultz <john.stultz@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Olof Johansson <olof@...om.net>, Wei Xu <xuwei5@...ilicon.com>,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM64: Kconfig: Fix the missing hi655x common clk

On 12/06/2017 23:12, Arnd Bergmann wrote:
> On Mon, Jun 12, 2017 at 11:38 AM, Daniel Lezcano
> <daniel.lezcano@...aro.org> wrote:
>> On Fri, Jun 09, 2017 at 10:48:13PM +0200, Arnd Bergmann wrote:
>>> On Fri, Jun 9, 2017 at 10:15 PM, John Stultz <john.stultz@...aro.org> wrote:
>>>> On Fri, Jun 9, 2017 at 1:06 PM, Arnd Bergmann <arnd@...db.de> wrote:
>>>>> On Fri, Jun 9, 2017 at 5:46 PM, Daniel Lezcano
>>>>> <daniel.lezcano@...aro.org> wrote:
>>>>>
>>>>> Yes, but I'm not sure this is the right patch either. We tend to not
>>>>> use 'select' for user-visible drivers, and most hisilicon platforms
>>>>> won't need this driver.
>>>>>
>>>>> I think it would be more consistent to add this to the defconfig
>>>>> and regard it as a user error when the driver is disabled on a
>>>>> machine that needs it.
>>>>
>>>> Maybe the select is not exactly in the right place, but I don't really
>>>> feel like a pmic on an SoC is a "user-visible driver". I deal with the
>>>> board often and when the new dependency was made on the clk, I would
>>>> have never have found it on my own w/o Ulf and Daniel pointing out
>>>> what I needed to enable.
>>>
>>> What I meant is that the Kconfig option is user-visible. On a very high
>>> level, this is a result of arch/arm64/Kconfig.platforms listing only
>>> very broad categories of SoCs, in many cases only the manufacturers
>>> of very different chip families, which then control the visibility of the
>>> individual Kconfig items for things like pinctrl or clk.
>>>
>>> I now see that MFD_HI655X_PMIC is the top-level driver that you
>>> have to select before enabling COMMON_CLK_HI655X, so the
>>> patch is actually broken unless it actually selects both.
>>>
>>> How about simply adding a 'default MFD_HI655X_PMIC' to
>>> COMMON_CLK_HI655X to enable it unless it is explicitly
>>> turned off?
>>
>> Actually, I share John's opinion.
>>
>> Ideally when we choose a platform, all the relevants devices configuration
>> options should be selected automatically from a single topmost node of a tree
>> (platform selection) to all the nodes corresponding to the devices, leaving the
>> user to select one simple option without knowledge of the SoC hardware
>> internals.
>>
>> If the user is expert in the platform and knows exactly what he does, then he
>> can select an _EXPERT_ like option and be able to disable some drivers.
>>
>> It is how I tend to write the Kconfig options, so the 'default MFD_HI655X_PMIC'
>> is confusing for me. Wouldn't make sense to select COMMON_CLK_HI655X when
>> MFD_HI655X_PMIC is enabled?
> 
> I don't think it's that easy. When you do that, MFD_HI655X_PMIC gains
> a dependency on COMMON_CLK and will again cause a warning on
> machines that disable that during compile testing.

This issue is related to the missing stubs in the includes.

> Using 'select' for user-selectable options generally leads to problems,
> and you are better off avoiding it. If you want to make the symbol impossible
> to turn off for non-EXPERT configurations, you can write it like
> 
> config COMMON_CLK_HI655X
>         tristate "Clock driver for Hi655x" if EXPERT
>         depends on (MFD_HI655X_PMIC || COMPILE_TEST)
>         depends on REGMAP
>         default MFD_HI655X_PMIC
> 
> That way the option is completely hidden for non-EXPERT,
> but still has the right default otherwise, and the dependencies
> are tracked right for compile-testing.

Ok.

Thanks!

  -- Daniel


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