linux-kernel - Re: [PATCH] x86: GEODE: cache results from geode_has

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Message-ID: <20080429165720.56a18253@ephemeral>
Date:	Tue, 29 Apr 2008 16:57:20 -0400
From:	Andres Salomon <dilinger@...ued.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	hpa@...or.com, mingo@...e.hu, linux-kernel@...r.kernel.org,
	jordan.crouse@....com
Subject: Re: [PATCH] x86: GEODE: cache results from geode_has_vsa2() and
 uninline

On Tue, 29 Apr 2008 13:35:12 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Tue, 29 Apr 2008 01:32:13 -0400
> Andres Salomon <dilinger@...ued.net> wrote:
> 
> > On Mon, 28 Apr 2008 20:06:51 -0700
> > Andrew Morton <akpm@...ux-foundation.org> wrote:
> > 
> > > On Mon, 21 Apr 2008 17:02:30 -0400 Andres Salomon <dilinger@...ued.net> wrote:
> > > 
> > > > +	if (!is_geode() || geode_has_vsa2())
> > > 
> > > geode_has_vsa2() is a fairly expensive-looking function and afacit only
> > > needs to be evaluated once per boot.  Perhaps we should cache it somewhere?
> > > 
> > 
> > How about this?
> > 
> 
> Looks sane.  Although one wonders if it should be cached as one of the
> standard x86 feature bit thingies which show up in /proc/cpuinfo's 'flags'
> field.
> 

The VSA lives in a weird place between hardware and BIOS.  I'm not
really sure whether it's appropriate for it to be an x86_cap_flags (it
hadn't occurred to me), but I think of it more as BIOS.  Jordan, what do
you think?



> > +static int has_vsa2 = -1;
> > +
> > +int geode_has_vsa2(void)
> > +{
> > +	if (has_vsa2 == -1) {
> > +		/*
> > +		 * The VSA has virtual registers that we can query for a
> > +		 * signature.
> > +		 */
> > +		outw(VSA_VR_UNLOCK, VSA_VRC_INDEX);
> > +		outw(VSA_VR_SIGNATURE, VSA_VRC_INDEX);
> > +
> > +		has_vsa2 = (inw(VSA_VRC_DATA) == VSA_SIG);
> > +	}
> > +
> > +	return has_vsa2;
> > +}
> > +EXPORT_SYMBOL_GPL(geode_has_vsa2);
> 
> nit:
> 
> --- a/arch/x86/kernel/geode_32.c
> +++ a/arch/x86/kernel/geode_32.c
> @@ -161,10 +161,10 @@ void geode_gpio_setup_event(unsigned int
>  }
>  EXPORT_SYMBOL_GPL(geode_gpio_setup_event);
>  
> -static int has_vsa2 = -1;
> -
>  int geode_has_vsa2(void)
>  {
> +	static int has_vsa2 = -1;
> +

Looks good.

Acked-by: Andres Salomon <dilinger@...ian.org>

>  	if (has_vsa2 == -1) {
>  		/*
>  		 * The VSA has virtual registers that we can query for a
> 


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