pseries: Export RTC time via QOM

On x86, the guest's RTC can be read with QMP, either from the RTC device's
"date" property or via the "rtc-time" property on the machine (which is an
alias to the former).  This is set up in the mc146818rtc driver, and
doesn't work on other targets.

This patch adds a similar "date" property to the pseries machine's RTAS RTC
and adds a compatible alias to the machine.
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NAlexander Graf <agraf@suse.de>

hw/ppc/spapr.c

@@ -1000,6 +1000,9 @@ static void spapr_rtc_create(sPAPREnvironment *spapr)
 
     qdev_init_nofail(dev);
     spapr->rtc = dev;
+
+    object_property_add_alias(qdev_get_machine(), "rtc-time",
+                              OBJECT(spapr->rtc), "date", NULL);
 }
 
 /* Returns whether we want to use VGA or not */

hw/ppc/spapr_rtc.c

@@ -152,6 +152,11 @@ static void rtas_set_time_of_day(PowerPCCPU *cpu, sPAPREnvironment *spapr,
     rtas_st(rets, 0, RTAS_OUT_SUCCESS);
 }
 
+static void spapr_rtc_qom_date(Object *obj, struct tm *current_tm, Error **errp)
+{
+    spapr_rtc_read(DEVICE(obj), current_tm, NULL);
+}
+
 static void spapr_rtc_realize(DeviceState *dev, Error **errp)
 {
     sPAPRRTCState *rtc = SPAPR_RTC(dev);
@@ -165,6 +170,8 @@ static void spapr_rtc_realize(DeviceState *dev, Error **errp)
     host_s = mktimegm(&tm);
     rtc_ns = qemu_clock_get_ns(rtc_clock);
     rtc->ns_offset = host_s * NSEC_PER_SEC - rtc_ns;
+
+    object_property_add_tm(OBJECT(rtc), "date", spapr_rtc_qom_date, NULL);
 }
 
 static const VMStateDescription vmstate_spapr_rtc = {