x86/time: split CMOS read and probe logic into function

The current logic to probe for the CMOS RTC is open-coded in get_cmos_time(),
move it to a separate function that both serves the purpose of testing for the
CMOS RTC existence and returning its value.

The goal is to be able to split the probing and the reading logic into separate
helpers, and putting the current logic in a separate function helps simplifying
further changes.

A transient *rtc_p variable is introduced as a parameter to the function, that
will be removed by further changes.  Also note that due to the code movement,
now cmos_rtc_probe will only get cleared on a second call to get_cmos_time(),
as the newly introduced cmos_probe() function doesn't modify the variable
anymore.

No functional change intended.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/time.c

@@ -1291,11 +1291,47 @@ static bool __get_cmos_time(struct rtc_time *rtc)
     return t1 <= SECONDS(1) && t2 < MILLISECS(3);
 }
 
+static bool cmos_probe(struct rtc_time *rtc_p, bool cmos_rtc_probe)
+{
+    unsigned int seconds = 60;
+
+    for ( ; ; )
+    {
+        bool success = __get_cmos_time(rtc_p);
+        struct rtc_time rtc = *rtc_p;
+
+        if ( likely(!cmos_rtc_probe) )
+            return true;
+
+        if ( !success ||
+             rtc.sec >= 60 || rtc.min >= 60 || rtc.hour >= 24 ||
+             !rtc.day || rtc.day > 31 ||
+             !rtc.mon || rtc.mon > 12 )
+            return false;
+
+        if ( seconds < 60 )
+        {
+            if ( rtc.sec != seconds )
+            {
+                acpi_gbl_FADT.boot_flags &= ~ACPI_FADT_NO_CMOS_RTC;
+                return true;
+            }
+            return false;
+        }
+
+        process_pending_softirqs();
+
+        seconds = rtc.sec;
+    }
+
+    ASSERT_UNREACHABLE();
+    return false;
+}
+
 static unsigned long get_cmos_time(void)
 {
     unsigned long res;
     struct rtc_time rtc;
-    unsigned int seconds = 60;
     static bool __read_mostly cmos_rtc_probe;
     boolean_param("cmos-rtc-probe", cmos_rtc_probe);
 
@@ -1312,32 +1348,7 @@ static unsigned long get_cmos_time(void)
         panic("System with no CMOS RTC advertised must be booted from EFI"
               " (or with command line option \"cmos-rtc-probe\")\n");
 
-    for ( ; ; )
-    {
-        bool success = __get_cmos_time(&rtc);
-
-        if ( likely(!cmos_rtc_probe) || !success ||
-             rtc.sec >= 60 || rtc.min >= 60 || rtc.hour >= 24 ||
-             !rtc.day || rtc.day > 31 ||
-             !rtc.mon || rtc.mon > 12 )
-            break;
-
-        if ( seconds < 60 )
-        {
-            if ( rtc.sec != seconds )
-            {
-                cmos_rtc_probe = false;
-                acpi_gbl_FADT.boot_flags &= ~ACPI_FADT_NO_CMOS_RTC;
-            }
-            break;
-        }
-
-        process_pending_softirqs();
-
-        seconds = rtc.sec;
-    }
-
-    if ( unlikely(cmos_rtc_probe) )
+    if ( !cmos_probe(&rtc, cmos_rtc_probe) )
         panic("No CMOS RTC found - system must be booted from EFI\n");
 
     return mktime(rtc.year, rtc.mon, rtc.day, rtc.hour, rtc.min, rtc.sec);