s390/idle: convert open coded idle time seqcount

s390 uses open coded seqcount to synchronize idle time accounting.
Lets consolidate it with the standard API.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/idle.h

@@ -9,9 +9,10 @@
 
 #include <linux/types.h>
 #include <linux/device.h>
+#include <linux/seqlock.h>
 
 struct s390_idle_data {
-	unsigned int sequence;
+	seqcount_t seqcount;
 	unsigned long long idle_count;
 	unsigned long long idle_time;
 	unsigned long long clock_idle_enter;

arch/s390/kernel/idle.c

@@ -38,15 +38,13 @@ void enabled_wait(void)
 	trace_hardirqs_off();
 
 	/* Account time spent with enabled wait psw loaded as idle time. */
-	idle->sequence++;
-	smp_wmb();
+	write_seqcount_begin(&idle->seqcount);
 	idle_time = idle->clock_idle_exit - idle->clock_idle_enter;
 	idle->clock_idle_enter = idle->clock_idle_exit = 0ULL;
 	idle->idle_time += idle_time;
 	idle->idle_count++;
 	account_idle_time(idle_time);
-	smp_wmb();
-	idle->sequence++;
+	write_seqcount_end(&idle->seqcount);
 }
 NOKPROBE_SYMBOL(enabled_wait);
 
@@ -55,14 +53,14 @@ static ssize_t show_idle_count(struct device *dev,
 {
 	struct s390_idle_data *idle = &per_cpu(s390_idle, dev->id);
 	unsigned long long idle_count;
-	unsigned int sequence;
+	unsigned int seq;
 
 	do {
-		sequence = ACCESS_ONCE(idle->sequence);
+		seq = read_seqcount_begin(&idle->seqcount);
 		idle_count = ACCESS_ONCE(idle->idle_count);
 		if (ACCESS_ONCE(idle->clock_idle_enter))
 			idle_count++;
-	} while ((sequence & 1) || (ACCESS_ONCE(idle->sequence) != sequence));
+	} while (read_seqcount_retry(&idle->seqcount, seq));
 	return sprintf(buf, "%llu\n", idle_count);
 }
 DEVICE_ATTR(idle_count, 0444, show_idle_count, NULL);
@@ -72,15 +70,15 @@ static ssize_t show_idle_time(struct device *dev,
 {
 	struct s390_idle_data *idle = &per_cpu(s390_idle, dev->id);
 	unsigned long long now, idle_time, idle_enter, idle_exit;
-	unsigned int sequence;
+	unsigned int seq;
 
 	do {
 		now = get_tod_clock();
-		sequence = ACCESS_ONCE(idle->sequence);
+		seq = read_seqcount_begin(&idle->seqcount);
 		idle_time = ACCESS_ONCE(idle->idle_time);
 		idle_enter = ACCESS_ONCE(idle->clock_idle_enter);
 		idle_exit = ACCESS_ONCE(idle->clock_idle_exit);
-	} while ((sequence & 1) || (ACCESS_ONCE(idle->sequence) != sequence));
+	} while (read_seqcount_retry(&idle->seqcount, seq));
 	idle_time += idle_enter ? ((idle_exit ? : now) - idle_enter) : 0;
 	return sprintf(buf, "%llu\n", idle_time >> 12);
 }
@@ -90,14 +88,14 @@ cputime64_t arch_cpu_idle_time(int cpu)
 {
 	struct s390_idle_data *idle = &per_cpu(s390_idle, cpu);
 	unsigned long long now, idle_enter, idle_exit;
-	unsigned int sequence;
+	unsigned int seq;
 
 	do {
 		now = get_tod_clock();
-		sequence = ACCESS_ONCE(idle->sequence);
+		seq = read_seqcount_begin(&idle->seqcount);
 		idle_enter = ACCESS_ONCE(idle->clock_idle_enter);
 		idle_exit = ACCESS_ONCE(idle->clock_idle_exit);
-	} while ((sequence & 1) || (ACCESS_ONCE(idle->sequence) != sequence));
+	} while (read_seqcount_retry(&idle->seqcount, seq));
 	return idle_enter ? ((idle_exit ?: now) - idle_enter) : 0;
 }