[PATCH 6/6] sbsa-gwdt: reschedule timer on direct WCV load

[Igor Mammedov <imammedo@redhat.com>]

According to spec[1]:

 "The compare value can either be loaded directly or indirectly on an
  explicit refresh or timeout refresh"

QEMU accepts writes to WCV but doesn't reschedule the timer,
which it should per the spec pseudo code:

 "TimeoutRefresh = ( SystemCounter [63:0] > CompareValue [63:0])"

Fix it by updating the timer on WCV write.

partialy[2] fixes Windows in GTDT mode, which never issues a WRR refresh.
Instead, it programs WOR to ~4 sec, enables WCS, and immediately
writes a large absolute value into WCV to push the timeout far
into the future. Without this, QEMU ignores the WCV write,
the short WOR expires, and the guest reboots unexpectedly.

1) Arm® Server Base System Architecture 6.0
   Platform Design Document
   DEN0029D 6.0
   "A.2 Watchdog Operation"
2) under KVM system counter (CNTPCT) as read by guest apprears to
   produce host's value, so watchdog timeout effectively gets
   extended on host uptime offset. But that's a separate issue
   to be fixed.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
 hw/watchdog/sbsa_gwdt.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/hw/watchdog/sbsa_gwdt.c b/hw/watchdog/sbsa_gwdt.c
index 0a1d981072..9ed109d6eb 100644
--- a/hw/watchdog/sbsa_gwdt.c
+++ b/hw/watchdog/sbsa_gwdt.c
@@ -148,6 +148,13 @@ static void sbsa_gwdt_wor_update_timer(SBSA_GWDTState *s, WdtRefreshType rtype)
     sbsa_gwdt_set_timer(s, timeout);
 }
 
+static void sbsa_gwdt_wcv_update_timer(SBSA_GWDTState *s)
+{
+    if (s->wcs & SBSA_GWDT_WCS_EN) {
+        sbsa_gwdt_set_timer(s, (uint64_t)s->wcvu << 32 | s->wcvl);
+    }
+}
+
 static void sbsa_gwdt_rwrite(void *opaque, hwaddr offset, uint64_t data,
                              unsigned size) {
     SBSA_GWDTState *s = SBSA_GWDT(opaque);
@@ -187,10 +194,12 @@ static void sbsa_gwdt_write(void *opaque, hwaddr offset, uint64_t data,
 
     case SBSA_GWDT_WCV:
         s->wcvl = data;
+        sbsa_gwdt_wcv_update_timer(s);
         break;
 
     case SBSA_GWDT_WCVU:
         s->wcvu = data;
+        sbsa_gwdt_wcv_update_timer(s);
         break;
 
     default:
-- 
2.52.0