[Patch 4/4] x86/hpet: Don't clear reserved bits in the General Configuration Register

[Andrew Cooper <andrew.cooper3@citrix.com>]

It is a violation of the specification.

The reserved bits in the General Configuration Register, unlike all other
reserved bits I have found in the spec, are specified as 'must never be
changed by the OS'.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
 xen/arch/x86/hpet.c        |   10 +++-------
 xen/include/asm-x86/hpet.h |    2 ++
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/hpet.c b/xen/arch/x86/hpet.c
index 091e624..eb48f84 100644
--- a/xen/arch/x86/hpet.c
+++ b/xen/arch/x86/hpet.c
@@ -814,15 +814,11 @@ void hpet_resume(u32 *boot_cfg)
     cfg = hpet_read32(HPET_CFG);
     if ( boot_cfg )
         *boot_cfg = cfg;
-    cfg &= ~(HPET_CFG_ENABLE | HPET_CFG_LEGACY);
-    if ( cfg )
-    {
+
+    if ( cfg & HPET_CFG_RESERVED )
         printk(XENLOG_WARNING
                "HPET: reserved bits %#x set in global config register\n",
-               cfg);
-        cfg = 0;
-    }
-    hpet_write32(cfg, HPET_CFG);
+               cfg & HPET_CFG_RESERVED);
 
     hpet_id = hpet_read32(HPET_ID);
     last = (hpet_id & HPET_ID_NUMBER) >> HPET_ID_NUMBER_SHIFT;
diff --git a/xen/include/asm-x86/hpet.h b/xen/include/asm-x86/hpet.h
index 875f1de..22a11da 100644
--- a/xen/include/asm-x86/hpet.h
+++ b/xen/include/asm-x86/hpet.h
@@ -28,6 +28,8 @@
 
 #define HPET_CFG_ENABLE	0x001
 #define HPET_CFG_LEGACY	0x002
+#define HPET_CFG_RESERVED 0xfffffffc
+
 #define	HPET_LEGACY_8254	2
 #define	HPET_LEGACY_RTC		8
 
-- 
1.7.10.4