linux-kernel - Re: [PATCH 20/22] clocksource/drivers/exynos_mct: Fix Kconfig and add COMPILE

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Message-ID: <563895C5.9000502@linaro.org>
Date:	Tue, 3 Nov 2015 12:08:53 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Krzysztof Kozlowski <k.kozlowski@...sung.com>, tglx@...utronix.de,
	john.stultz@...aro.org, linux-kernel@...r.kernel.org,
	Russell King <linux@....linux.org.uk>,
	Kukjin Kim <kgene@...nel.org>,
	"moderated list:ARM SUB-ARCHITECT..." 
	<linux-arm-kernel@...ts.infradead.org>,
	"moderated list:ARM/SAMSUNG EXYNO..." 
	<linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCH 20/22] clocksource/drivers/exynos_mct: Fix Kconfig and add
 COMPILE_TEST option

On 11/03/2015 11:02 AM, Arnd Bergmann wrote:
> On Tuesday 03 November 2015 09:40:02 Daniel Lezcano wrote:
>> On 11/03/2015 01:59 AM, Krzysztof Kozlowski wrote:
>>> On 03.11.2015 09:30, Krzysztof Kozlowski wrote:
>>>> On 02.11.2015 21:56, Daniel Lezcano wrote:
>>>>> Let the platform's Kconfig to select the clock instead of having a reverse
>>>>> dependency from the driver to the platform options.
>>>>
>>>> Selecting user-visible symbols is rather discouraged so why not
>>>> something like this:
>>>>
>>>> -       def_bool y if ARCH_EXYNOS
>>>> -       depends on !ARM64
>>>> +       bool "Exynos multi core timer driver"
>>>> +       depends on ARCH_EXYNOS || (COMPILE_TEST && ARM)
>>>
>>> Nope, that was wrong as we loose auto-select on Exynos. Instead:
>>> -       def_bool y if ARCH_EXYNOS
>>> -       depends on !ARM64
>>> +       bool "Exynos multi core timer driver" if ARM
>>> +       depends on ARCH_EXYNOS || COMPILE_TEST
>>> +       default y if ARCH_EXYNOS
>>>
>>> This way we avoid select (which is a reverse dependency for the driver),
>>> have it auto-selectable and compile tested on arm.
>>
>> I think you misunderstood the patch I sent.
>>
>> It does two things:
>>
>> 1. Follow the thumb of rule of the current Kconfig format
>>
>>      - The timer driver is selected by the platform (exynos in this case)
>>      - User can't select the driver in the menuconfig
>>      - There is no dependency on the platform except for compilation test
>>
>> 2. Add the COMPILE_TEST
>>
>>      - User can select the driver for compilation testing. This is for
>> allyesconfig when doing compilation test coverage (exynos timer could be
>> compiled on other platform). As the delay code is not portable, we have
>> to restrict the compilation on the ARM platform, this is why there is
>> the dependency on ARM.
>>
>> I am currently looking at splitting the delay code in order to prevent
>> this restriction on this driver and some others drivers.
>
> I suspect this will come up again in the future. The problem is
> really that drivers/clocksource has different rules from almost
> everything else, by requiring the platform to 'select' the driver.
>
> The second version that Krzysztof posted is how we handle this in
> other driver subsystems, and I would generally prefer it to do this
> consistently for everything, but John Stultz has in the past argued
> strongly for using 'select' in all clocksource drivers. The reason
> is that for each platform we know in advance which driver we want,
> and there is never a need for the user to have to select the right
> one.

Yes, and I second John in this.



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