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

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Message-Id: <20080429133512.fcd8f8dd.akpm@linux-foundation.org>
Date:	Tue, 29 Apr 2008 13:35:12 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andres Salomon <dilinger@...ued.net>
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 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.

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

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