x86: GEODE: add Virtual Systems Architecture detection

This is generic VSA2 detection.  It's used by OLPC to determine whether or not
the BIOS contains VSA2, but since other BIOSes are coming out that don't use
the VSA (ie, tinybios), it might end up being useful for others.
Signed-off-by: Andres Salomon <dilinger@debian.org>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Jordan Crouse <jordan.crouse@amd.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/asm-x86/geode.h

@@ -103,6 +103,14 @@ extern int geode_get_dev_base(unsigned int dev);
 #define PM_AWKD			0x50
 #define PM_SSC			0x54
 
+/* VSA2 magic values */
+
+#define VSA_VRC_INDEX		0xAC1C
+#define VSA_VRC_DATA		0xAC1E
+#define VSA_VR_UNLOCK		0xFC53	/* unlock virtual register */
+#define VSA_VR_SIGNATURE	0x0003
+#define VSA_SIG			0x4132	/* signature is ascii 'VSA2' */
+
 /* GPIO */
 
 #define GPIO_OUTPUT_VAL		0x00
@@ -174,6 +182,17 @@ static inline int is_geode(void)
 	return (is_geode_gx() || is_geode_lx());
 }
 
+/*
+ * The VSA has virtual registers that we can query for a signature.
+ */
+static inline int geode_has_vsa2(void)
+{
+	outw(VSA_VR_UNLOCK, VSA_VRC_INDEX);
+	outw(VSA_VR_SIGNATURE, VSA_VRC_INDEX);
+
+	return (inw(VSA_VRC_DATA) == VSA_SIG);
+}
+
 /* MFGPTs */
 
 #define MFGPT_MAX_TIMERS	8