linux-kernel - Re: [PATCH v4 12/24] xen/arm: introduce CONFIG

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Message-ID: <alpine.DEB.2.02.1209171527210.29232@kaball.uk.xensource.com>
Date:	Mon, 17 Sep 2012 15:30:28 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>
CC:	Sergei Shtylyov <sshtylyov@...sta.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linaro-dev@...ts.linaro.org" <linaro-dev@...ts.linaro.org>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"catalin.marinas@....com" <catalin.marinas@....com>,
	"Tim (Xen.org)" <tim@....org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 12/24] xen/arm: introduce CONFIG_XEN on ARM

On Mon, 17 Sep 2012, Stefano Stabellini wrote:
> On Mon, 17 Sep 2012, Sergei Shtylyov wrote:
> > Hello.
> > 
> > On 17-09-2012 14:57, Stefano Stabellini wrote:
> > 
> > >>> Changes in v2:
> > 
> > >>> - mark Xen guest support on ARM as EXPERIMENTAL.
> > 
> > >>> Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> > >>> Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > >>> ---
> > >>>   arch/arm/Kconfig |   10 ++++++++++
> > >>>   1 files changed, 10 insertions(+), 0 deletions(-)
> > 
> > >>> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > >>> index 2f88d8d..e92518d 100644
> > >>> --- a/arch/arm/Kconfig
> > >>> +++ b/arch/arm/Kconfig
> > >>> @@ -1897,6 +1897,16 @@ config DEPRECATED_PARAM_STRUCT
> > >>>   	  This was deprecated in 2001 and announced to live on for 5 years.
> > >>>   	  Some old boot loaders still use this way.
> > >>>
> > >>> +config XEN_DOM0
> > >>> +	def_bool y
> > >>> +
> > >>> +config XEN
> > >>> +	bool "Xen guest support on ARM (EXPERIMENTAL)"
> > >>> +	depends on EXPERIMENTAL && ARM && OF
> > >>> +	select XEN_DOM0
> > 
> > >>     What's the point of selecting it if it's always "y"?
> > 
> > > That's because on X86 is not always "y": there are things under
> > > drivers/xen that compile on both platforms and depend on XEN_DOM0.
> > 
> >     But we're not on x86. On ARM this select is pointless.
> 
> We need some common code (under drivers/xen) that compiles only if
> XEN_DOM0 is selected, so it is not pointless after all.
> 
> XEN_DOM0 is not the only symbol that is conditionally compiled on one
> architectuire and always "y" on another...
> 

Wait a sec, I have just realized that written this way XEN_DOM0 is
always "y", even if XEN is not!
The right way of doing this is:


config XEN_DOM0
	def_bool y
	depends on XEN

config XEN
	bool "Xen guest support on ARM (EXPERIMENTAL)"
	depends on EXPERIMENTAL && ARM && OF
	help
	  Say Y if you want to run Linux in a Virtual Machine on Xen on ARM.


I am not sure if this is what you meant, but thanks for making me
realize this mistake anyway! :)
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