[PATCH] Elan BIOS quirk workaround.

Marc Singer noticed some BIOSen on the AMD Elan
alias the cpu frequency registers in a place that some
drivers probe during bootup. Result - changed CPU speed
after booting.

The fix is to unmap the alias.

Marc put a patch forward for 2.2, this one is cooked up
by me, but is currently untested but functionally equivalent.

arch/i386/kernel/cpu/amd.c

@@ -42,6 +42,21 @@ static void __init init_amd(struct cpuinfo_x86 *c)
 
 	switch(c->x86)
 	{
+		case 4:
+		/*
+		 * General Systems BIOSen alias the cpu frequency registers
+		 * of the Elan at 0x000df000. Unfortuantly, one of the Linux
+		 * drivers subsequently pokes it, and changes the CPU speed.
+		 * Workaround : Remove the unneeded alias.
+		 */
+#define CBAR		(0xfffc) /* Configuration Base Address  (32-bit) */
+#define CBAR_ENB	(0x80000000)
+#define CBAR_KEY	(0X000000CB)
+			if (c->x86_model==9 || c->x86_model == 10) {
+				if (inl (CBAR) & CBAR_ENB)
+					outl (0 | CBAR_KEY, CBAR);
+			}
+
 		case 5:
 			if( c->x86_model < 6 )
 			{