[Xen-changelog] [xen-3.1-testing] hvm: RTC emulation - RTC_UIE/RTC_SET fix

["Xen patchbot-3.1-testing" <patchbot-3.1-testing@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1196958966 0
# Node ID 987025d210cd2bd1bff2ecc65d948b45d39cca27
# Parent  120de16f76d4690a22c9e45c948c7b59fd3b49c1
hvm: RTC emulation - RTC_UIE/RTC_SET fix

This patch fixes a bug in the RTC code which appears to originate in
having written the emuated device following an incorrect
specification. VMware has (or had, at least, at the time we were still
testing on both VMWare and Xen) the same issue. In the current code,
when RTC_SET is set, RTC_UIE is cleared. This does not match the
behavior of real hardware, where the case is simply that no update
ended interrupts are sent as long as RTC_SET is set, but the UE ints
will resume as soon as RTC_SET is cleared and the clock update is
done. This little patch fixes this issue. In practicality, this means
OS/2 can now set the time without having the clock stop. I don't know
if any other guests have been affected by this issue.

From: Trolle Selander <trolle.selander@xxxxxxxxx>
Signed-off-by: Keir Fraser <keir.fraser@xxxxxxxxxx>
xen-unstable changeset:   16394:86e4b37a06ccc6c7c0ea75b5af9e6116b5d6a382
xen-unstable date:        Fri Nov 16 19:07:46 2007 +0000
---
 xen/arch/x86/hvm/rtc.c |    3 +--
 1 files changed, 1 insertion(+), 2 deletions(-)

diff -r 120de16f76d4 -r 987025d210cd xen/arch/x86/hvm/rtc.c
--- a/xen/arch/x86/hvm/rtc.c    Thu Dec 06 16:35:37 2007 +0000
+++ b/xen/arch/x86/hvm/rtc.c    Thu Dec 06 16:36:06 2007 +0000
@@ -128,7 +128,6 @@ static int rtc_ioport_write(void *opaque
         {
             /* set mode: reset UIP mode */
             s->hw.cmos_data[RTC_REG_A] &= ~RTC_UIP;
-            data &= ~RTC_UIE;
         }
         else
         {
@@ -350,7 +349,7 @@ static void rtc_update_second2(void *opa
     }
 
     /* update ended interrupt */
-    if ( s->hw.cmos_data[RTC_REG_B] & RTC_UIE )
+    if ( (s->hw.cmos_data[RTC_REG_B] & (RTC_UIE|RTC_SET)) == RTC_UIE )
     {
         s->hw.cmos_data[RTC_REG_C] |= 0x90; 
         hvm_isa_irq_deassert(d, RTC_IRQ);

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