[Xen-devel] [PATCH 3/4] x86/hpet: clear unwanted bits

["Jan Beulich" <JBeulich@xxxxxxxx>]

Leaving certain bits set when being started from an environment where
the HPET was already in use can affect functionality. Clear those bits
to be on the safe side.

We should also consider ignoring the HPET altogether if any reserved
bits are found to be set.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hpet.c
+++ b/xen/arch/x86/hpet.c
@@ -537,7 +537,7 @@ void __init hpet_broadcast_init(void)
     {
         /* set HPET Tn as oneshot */
         cfg = hpet_read32(HPET_Tn_CFG(hpet_events[i].idx));
-        cfg &= ~HPET_TN_PERIODIC;
+        cfg &= ~(HPET_TN_LEVEL | HPET_TN_PERIODIC | HPET_TN_FSB);
         cfg |= HPET_TN_ENABLE | HPET_TN_32BIT;
         hpet_write32(cfg, HPET_Tn_CFG(hpet_events[i].idx));
 
@@ -594,7 +594,7 @@ void hpet_broadcast_resume(void)
 
         /* set HPET Tn as oneshot */
         cfg = hpet_read32(HPET_Tn_CFG(hpet_events[i].idx));
-        cfg &= ~HPET_TN_PERIODIC;
+        cfg &= ~(HPET_TN_LEVEL | HPET_TN_PERIODIC | HPET_TN_FSB);
         cfg |= HPET_TN_ENABLE | HPET_TN_32BIT;
         hpet_write32(cfg, HPET_Tn_CFG(hpet_events[i].idx));
 
--- a/xen/include/asm-x86/hpet.h
+++ b/xen/include/asm-x86/hpet.h
@@ -32,9 +32,11 @@
 #define        HPET_LEGACY_8254        2
 #define        HPET_LEGACY_RTC         8
 
+#define HPET_TN_LEVEL          0x002
 #define HPET_TN_ENABLE         0x004
 #define HPET_TN_PERIODIC       0x008
 #define HPET_TN_PERIODIC_CAP   0x010
+#define HPET_TN_64BIT_CAP      0x020
 #define HPET_TN_SETVAL         0x040
 #define HPET_TN_32BIT          0x100
 #define HPET_TN_ROUTE          0x3e00

Attachment: x86-hpet-clear-unwanted-bits.patch
Description: Text document

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