netdev - Re: [PATCH] drivers/ptp/Kconfig: add "depends on HAS_IOMEM" for 'PTP_1588_CLOCK

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Date:	Mon, 1 Jul 2013 09:56:04 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Chen Gang <gang.chen@...anux.com>
Cc:	Richard Weinberger <richard@....at>,
	David Miller <davem@...emloft.net>,
	Richard Cochran <richardcochran@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] drivers/ptp/Kconfig: add "depends on HAS_IOMEM" for 'PTP_1588_CLOCK_PCH'

On Mon, Jul 1, 2013 at 9:47 AM, Chen Gang <gang.chen@...anux.com> wrote:
> On 07/01/2013 03:32 PM, Geert Uytterhoeven wrote:
>> On Mon, Jul 1, 2013 at 8:44 AM, Chen Gang <gang.chen@...anux.com> wrote:
>>> > On 07/01/2013 02:34 PM, Richard Weinberger wrote:
>>>>> >>> config COMPILE_TEST
>>>>>> >>> >         bool "Compile also drivers which will not load"
>>>>>> >>> >         default n
>>>>>> >>> >         help
>>>>>> >>> >           Some drivers can be compiled on a different platform than they are
>>>>>> >>> >           intended to be run on. Despite they cannot be loaded there (or even
>>>>>> >>> >           when they load they cannot be used due to missing HW support),
>>>>>> >>> >           developers still, opposing to distributors, might want to build such
>>>>>> >>> >           drivers to compile-test them.
>>>>>> >>> >
>>>>>> >>> >           If you are a developer and want to build everything available, say Y
>>>>>> >>> >           here. If you are a user/distributor, say N here to exclude useless
>>>>>> >>> >           drivers to be distributed.
>>>>>> >>> >
>>>>>> >>> > I guess, 'COMPILE_TEST' is really useful for UML.
>>>> >> No.
>>>> >>
>>>> >> We have explained you more than once what the deal and why UML does not
>>>> >> have ioremap() and friends.
>>> >
>>> > This time, it is not for UML, it is for 'COMPILE_TEST': the
>>> > 'asm-generic' whether need consider it.
>> COMPILE_TEST is only meant to be used as a dependency in Kconfig files,
>> to make drivers that cannot work due to missing hardware invisible when
>> configuring your kernel.
>
> Why "Despite they cannot be loaded there (or even when they load they
> cannot be used due to missing HW support)" ?
>
>> There should be no #ifdefs in actual code that check for (the lack of)
>> CONFIG_COMPILE_TEST.
>
> In ideal world, it should be no #ifdefs for all "CONFIG_*" in 'normal code'.
>
> But "asm-generic" are not belong to 'normal code', it is one of the main
> place to process "CONFIG_*".
>
> If the platforms need support 'COMPILE_TEST', the asm-generic is the
> main place for implementing it.
>
> So I think our focus is on "whether the platforms guys need support
> 'COMPILE_TEST" for modules guys".

COMPILE_TEST is to be used as a dependency if the code would compile,
but would not run. Adding fixes in the code to make more code compile is not
the job of COMPILE_TEST.

If we follow your reasoning, we can add dummy variants of all hardware support
that lives in arch/*/include/asm to asm-generic, so everything would compile
for all platforms. But that's now what we want.

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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