Revert "parisc: Mark cr16 CPU clocksource unstable on all SMP machines"

This reverts commit afdb4a5.

It triggers RCU stalls at boot with a 32-bit kernel.

Signed-off-by: Helge Deller <deller@gmx.de>
Noticed-by: John David Anglin <dave.anglin@bell.net>
Cc: stable@vger.kernel.org # v5.16+

Author: hdeller

arch/parisc/kernel/time.c

@@ -251,16 +251,30 @@ void __init time_init(void)
 static int __init init_cr16_clocksource(void)
 {
 	/*
-	 * The cr16 interval timers are not syncronized across CPUs, even if
-	 * they share the same socket.
+	 * The cr16 interval timers are not syncronized across CPUs on
+	 * different sockets, so mark them unstable and lower rating on
+	 * multi-socket SMP systems.
 	 */
 	if (num_online_cpus() > 1 && !running_on_qemu) {
-		/* mark sched_clock unstable */
-		clear_sched_clock_stable();
-
-		clocksource_cr16.name = "cr16_unstable";
-		clocksource_cr16.flags = CLOCK_SOURCE_UNSTABLE;
-		clocksource_cr16.rating = 0;
+		int cpu;
+		unsigned long cpu0_loc;
+		cpu0_loc = per_cpu(cpu_data, 0).cpu_loc;
+
+		for_each_online_cpu(cpu) {
+			if (cpu == 0)
+				continue;
+			if ((cpu0_loc != 0) &&
+			    (cpu0_loc == per_cpu(cpu_data, cpu).cpu_loc))
+				continue;
+
+			/* mark sched_clock unstable */
+			clear_sched_clock_stable();
+
+			clocksource_cr16.name = "cr16_unstable";
+			clocksource_cr16.flags = CLOCK_SOURCE_UNSTABLE;
+			clocksource_cr16.rating = 0;
+			break;
+		}
 	}
 
 	/* register at clocksource framework */