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Date: Sun, 3 Feb 2008 08:51:11 +0100
From: Sam Ravnborg <sam@ravnborg.org>
To: David Brownell <david-b@pacbell.net>
Cc: Ingo Molnar <mingo@elte.hu>, Pavel Machek <pavel@ucw.cz>,
       linux-pm@lists.linux-foundation.org,
       kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [linux-pm] sleepy linux self-test
Message-ID: <20080203075111.GB19981@uranus.ravnborg.org>
References: <20080130131748.GA3796@elf.ucw.cz> <20080203050537.GA18942@elte.hu> <20080203051425.GA20740@elte.hu> <200802022318.03597.david-b@pacbell.net>
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> --- g26.orig/drivers/char/Kconfig
> +++ g26/drivers/char/Kconfig
> @@ -715,9 +715,12 @@ config NVRAM
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called nvram.
>  
> +comment "You are using the RTC framework, not the legacy CMOS RTC driver"
> +	depends on RTC_DRV_CMOS
> +
>  config RTC
>  	tristate "Enhanced Real Time Clock Support"
> -	depends on !PPC && !PARISC && !IA64 && !M68K && !SPARC && !FRV && !ARM && !SUPERH && !S390
> +	depends on !PPC && !PARISC && !IA64 && !M68K && !SPARC && !FRV && !ARM && !SUPERH && !S390 && !RTC_DRV_CMOS

This looks like a prime candidate for a HAVE_RTC config variable
So you do:

 config RTC
 	tristate "Enhanced Real Time Clock Support"
+	depends on HAVE_RTC && !RTC_DEV_CMOS

config HAVE_RTC
	bool

(No "depends on" allowed!)


And then the architectures that do support the RTC Framework do an:
(arch/x86/Kconfig as an example):
 config X86
+	select HAVE_RTC

So when PPC suddenly supports it they add this single
select statement and no more Kconfig magic needed.

See Documentation/kbuild/kconfig-language.txt for a bit more elaborate
description.

	Sam