x86, hpet: check hpet existence

Add check on hpet existence which is removed accidentally
in previous changeset (18790). Or else BAD PERIOD error can be seen.

Signed-off-by: Kevin Tian <kevin.tian@intel.com>

diff --git a/xen/arch/x86/hpet.c b/xen/arch/x86/hpet.c
index d5e84f4ccd26af8114fb6ef56c82bab3574be736..f82221bbe21367a9ee8d7704c42ce17367d4568a 100644 (file)
--- a/xen/arch/x86/hpet.c
+++ b/xen/arch/x86/hpet.c
@@ -273,6 +273,9 @@ u64 hpet_setup(void)
         return hpet_rate;
     system_reset_latch = system_reset_counter;
 
+    if ( hpet_address == 0 )
+        return 0;
+
     set_fixmap_nocache(FIX_HPET_BASE, hpet_address);
 
     hpet_id = hpet_read32(HPET_ID);