x86: add force_hpet boot option

add force_hpet boot option.

(this will be useful to make the forced-enable quirks depend on.)

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 189df0b..c6859b9 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -431,8 +431,10 @@
 			over the 8254 in addition to over the IO-APIC. The
 			kernel tries to set a sensible default.
 
-	hpet=		[X86-32,HPET] option to disable HPET and use PIT.
-			Format: disable
+	hpet=		[X86-32,HPET] option to control HPET usage
+			Format: { enable (default) | disable | force }
+			disable: disable HPET and use PIT instead
+			force: allow force enabled of undocumented chips (ICH4, VIA)
 
 	com20020=	[HW,NET] ARCnet - COM20020 chipset
 			Format: