linux-kernel - Re: [GIT] kbuild: kconfig changes

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Date:	Tue, 10 Aug 2010 16:04:52 +0200
From:	Michal Marek <mmarek@...e.cz>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Arve Hj?nnev?g <arve@...roid.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	JBeulich@...ell.com, aris@...hat.com, catalin.marinas@....com,
	jacmet@...site.dk, justinmattock@...il.com, lizf@...fujitsu.com,
	ulfalizer.lkml@...il.com, zippel@...ux-m68k.org,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [GIT] kbuild: kconfig changes

On 8.8.2010 17:57, Sam Ravnborg wrote:
> On Fri, Aug 06, 2010 at 09:43:24PM -0700, Arve Hj?nnev?g wrote:
>> On Fri, Aug 6, 2010 at 9:01 PM, Sam Ravnborg <sam@...nborg.org> wrote:
>>>>
>>>> This change prevents some the minimal defconfig options from working.
>>>> Specifically our usb gadget drivers do not get set.
>>>
>>> Can you help me reproduce this?
>>>
>>> I have found an issue with choice values in combination with
>>> tristate logic that fails. I hope this is something similar.
>>>
>>
>> It is probably the same problem. The gadget driver that was not set is
>> not buildable as a module (it is not in the mainline kernel). If I
>> select another gadget driver instead it just gets changed to build as
>> a module instead.
>>
>> If you create a file, arch/arm/configs/test_defconfig with the following:
>> CONFIG_MODULES=y
>> CONFIG_USB_GADGET=y
>> CONFIG_USB_MASS_STORAGE=y
>>
>> then "make test_defconfig" results in .config having:
>> CONFIG_USB_MASS_STORAGE=m
>>
>>  (at least if you are set up to compile for arm)
> 
> Thanks Arve.
> 
> I have it reproduced now with a simple Kconfig:
> 
> $ cat Kconfig
> config M
> 	def_bool y
> 	option modules
> 
> choice
> 	prompt "choice list"
> 
> config A
> 	tristate "a"
> 
> config B
> 	tristate "b"
> 
> endchoice
> 
> $cat defconfig
> CONFIG_M=y
> CONFIG_A=y
> # CONFIG_B is not set
> 
> 
> If I do:
> 
>     $scripts/kconfig/conf --defconfig=defconfig Kconfig
> 
> with the above input the resulting .config is OK.
> 
> But If I drop the line:
> 
>     # CONFIG_B is not set
> 
> in the defconfig file then I end with CONFIG_A set to m.
> And this is not as expected - I cannot see why it should matter
> if we specify the value of B or not.
> 
> What we see here is that savedefconfig trigger a bug in the
> other part of kconfig - a bug which was not exposed before.
> 
> The reason why your patch cured it was that we then no
> longer triggered the bug (at least I guess so I did not look to close).
> 
> I will look into this as time permits. I assume the fix is simple
> when I find the reason.

I'm looking into it now, but understanding the kconfig internals is not
easy...

Michal
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