[Qemu-ppc] [RFC PATCH 3/3] pseries: Make RTAS time of day functions respect -rtc options

[David Gibson]

In the 'pseries' machine the real time clock is provided by a
paravirtualized firmware interface rather than a device per se; the RTAS
get-time-of-day and set-time-of-day calls.

Out current implementations of those work directly off host time (with
an offset), not respecting options such as clock=vm which can be
specified in the -rtc command line option.

This patch reworks the RTAS RTC code to respect those options, primarily
by basing them on the qemu_clock_get_ns(rtc_clock) function instead of
directly on qemu_get_timedate() (which essentially handles host time, not
virtual rtc time).

As a bonus, this means our get-time-of-day function now also returns
nanoseconds.

Signed-off-by: David Gibson <address@hidden>
---
 hw/ppc/spapr_rtc.c | 36 ++++++++++++++++++++++++++++++++----
 1 file changed, 32 insertions(+), 4 deletions(-)

diff --git a/hw/ppc/spapr_rtc.c b/hw/ppc/spapr_rtc.c
index 13eeab8..58715d2 100644
--- a/hw/ppc/spapr_rtc.c
+++ b/hw/ppc/spapr_rtc.c
@@ -26,6 +26,7 @@
  *
  */
 #include "cpu.h"
+#include "sysemu/sysemu.h"
 #include "hw/ppc/spapr.h"
 #include "qapi-event.h"
 
@@ -35,13 +36,18 @@ static void rtas_get_time_of_day(PowerPCCPU *cpu, 
sPAPREnvironment *spapr,
                                  uint32_t nret, target_ulong rets)
 {
     struct tm tm;
+    int64_t host_ns;
+    time_t guest_s;
 
     if ((nargs != 0) || (nret != 8)) {
         rtas_st(rets, 0, RTAS_OUT_PARAM_ERROR);
         return;
     }
 
-    qemu_get_timedate(&tm, spapr->rtc_offset);
+    host_ns = qemu_clock_get_ns(rtc_clock);
+
+    guest_s = host_ns / 1000000000LL + spapr->rtc_offset;
+    gmtime_r(&guest_s, &tm);
 
     rtas_st(rets, 0, RTAS_OUT_SUCCESS);
     rtas_st(rets, 1, tm.tm_year + 1900);
@@ -50,7 +56,7 @@ static void rtas_get_time_of_day(PowerPCCPU *cpu, 
sPAPREnvironment *spapr,
     rtas_st(rets, 4, tm.tm_hour);
     rtas_st(rets, 5, tm.tm_min);
     rtas_st(rets, 6, tm.tm_sec);
-    rtas_st(rets, 7, 0); /* we don't do nanoseconds */
+    rtas_st(rets, 7, host_ns % 1000000000LL);
 }
 
 static void rtas_set_time_of_day(PowerPCCPU *cpu, sPAPREnvironment *spapr,
@@ -59,6 +65,8 @@ static void rtas_set_time_of_day(PowerPCCPU *cpu, 
sPAPREnvironment *spapr,
                                  uint32_t nret, target_ulong rets)
 {
     struct tm tm;
+    time_t new_s;
+    int64_t host_ns;
 
     if ((nargs != 7) || (nret != 1)) {
         rtas_st(rets, 0, RTAS_OUT_PARAM_ERROR);
@@ -72,15 +80,35 @@ static void rtas_set_time_of_day(PowerPCCPU *cpu, 
sPAPREnvironment *spapr,
     tm.tm_min = rtas_ld(args, 4);
     tm.tm_sec = rtas_ld(args, 5);
 
-    /* Just generate a monitor event for the change */
+    new_s = mktimegm(&tm);
+    if (new_s == -1) {
+        rtas_st(rets, 0, RTAS_OUT_PARAM_ERROR);
+        return;
+    }
+
+    /* Generate a monitor event for the change */
     qapi_event_send_rtc_change(qemu_timedate_diff(&tm), &error_abort);
-    spapr->rtc_offset = qemu_timedate_diff(&tm);
+
+    host_ns = qemu_clock_get_ns(rtc_clock);
+
+    spapr->rtc_offset = new_s - host_ns / 1000000000L;
 
     rtas_st(rets, 0, RTAS_OUT_SUCCESS);
 }
 
 void spapr_rtc_init(void)
 {
+    struct tm tm;
+    time_t host_s;
+    int64_t rtc_ns;
+
+    /* Initialize the RTAS RTC from host time */
+
+    qemu_get_timedate(&tm, 0);
+    host_s = mktimegm(&tm);
+    rtc_ns = qemu_clock_get_ns(rtc_clock);
+    spapr->rtc_offset = host_s - rtc_ns / 1000000000LL;
+
     spapr_rtas_register(RTAS_GET_TIME_OF_DAY, "get-time-of-day",
                         rtas_get_time_of_day);
     spapr_rtas_register(RTAS_SET_TIME_OF_DAY, "set-time-of-day",
-- 
2.1.0