parisc: Enhance detection of synchronous cr16 clocksources

The cr16 clocks of the physical PARISC CPUs are usually nonsynchronous.
Nevertheless, it seems that each CPU socket (which holds two cores) of
PA8800 and PA8900 CPUs (e.g. in a C8000 workstation) is fed by the same
clock source, which makes the cr16 clocks of each CPU socket syncronous.
Let's try to detect such situations and mark the cr16 clocksource stable
on single-socket and single-core machines.

Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/include/asm/processor.h

@@ -103,6 +103,8 @@ struct cpuinfo_parisc {
 	unsigned long bh_count;     /* number of times bh was invoked */
 	unsigned long fp_rev;
 	unsigned long fp_model;
+	unsigned long cpu_num;      /* CPU number from PAT firmware */
+	unsigned long cpu_loc;      /* CPU location from PAT firmware */
 	unsigned int state;
 	struct parisc_device *dev;
 	unsigned long loops_per_jiffy;

arch/parisc/kernel/processor.c

@@ -94,7 +94,7 @@ static int processor_probe(struct parisc_device *dev)
 	unsigned long txn_addr;
 	unsigned long cpuid;
 	struct cpuinfo_parisc *p;
-	struct pdc_pat_cpu_num cpu_info __maybe_unused;
+	struct pdc_pat_cpu_num cpu_info = { };
 
 #ifdef CONFIG_SMP
 	if (num_online_cpus() >= nr_cpu_ids) {
@@ -113,6 +113,7 @@ static int processor_probe(struct parisc_device *dev)
 	 */
 	cpuid = boot_cpu_data.cpu_count;
 	txn_addr = dev->hpa.start;	/* for legacy PDC */
+	cpu_info.cpu_num = cpu_info.cpu_loc = cpuid;
 
 #ifdef CONFIG_64BIT
 	if (is_pdc_pat()) {
@@ -180,6 +181,8 @@ static int processor_probe(struct parisc_device *dev)
 	p->hpa = dev->hpa.start;	/* save CPU hpa */
 	p->cpuid = cpuid;	/* save CPU id */
 	p->txn_addr = txn_addr;	/* save CPU IRQ address */
+	p->cpu_num = cpu_info.cpu_num;
+	p->cpu_loc = cpu_info.cpu_loc;
 #ifdef CONFIG_SMP
 	/*
 	** FIXME: review if any other initialization is clobbered

arch/parisc/kernel/time.c

@@ -243,14 +243,30 @@ void __init time_init(void)
 static int __init init_cr16_clocksource(void)
 {
 	/*
-	 * The cr16 interval timers are not syncronized across CPUs, so mark
-	 * them unstable and lower rating on SMP systems.
+	 * 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) {
-		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 (cpu0_loc == per_cpu(cpu_data, cpu).cpu_loc)
+				continue;
+
+			clocksource_cr16.name = "cr16_unstable";
+			clocksource_cr16.flags = CLOCK_SOURCE_UNSTABLE;
+			clocksource_cr16.rating = 0;
+			break;
+		}
 	}
 
+	/* XXX: We may want to mark sched_clock stable here if cr16 clocks are
+	 *	in sync:
+	 *	(clocksource_cr16.flags == CLOCK_SOURCE_IS_CONTINUOUS) */
+
 	/* register at clocksource framework */
 	clocksource_register_hz(&clocksource_cr16,
 		100 * PAGE0->mem_10msec);