linux-kernel - [PATCH 5.17 105/140] parisc: Mark cr16 clock unstable on all SMP machines

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Date:   Tue, 10 May 2022 15:08:15 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Helge Deller <deller@....de>
Subject: [PATCH 5.17 105/140] parisc: Mark cr16 clock unstable on all SMP machines

From: Helge Deller <deller@....de>

commit 340233dcc0160aafcce46ca893d1679f16acf409 upstream.

The cr16 interval timers are not synchronized across CPUs, even with just
one dual-core CPU. This becomes visible if the machines have a longer
uptime.

Signed-off-by: Helge Deller <deller@....de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/parisc/kernel/time.c |   27 ++++-----------------------
 1 file changed, 4 insertions(+), 23 deletions(-)

--- a/arch/parisc/kernel/time.c
+++ b/arch/parisc/kernel/time.c
@@ -249,33 +249,14 @@ void __init time_init(void)
 static int __init init_cr16_clocksource(void)
 {
 	/*
-	 * The cr16 interval timers are not syncronized across CPUs on
-	 * different sockets, so mark them unstable and lower rating on
-	 * multi-socket SMP systems.
+	 * The cr16 interval timers are not synchronized across CPUs.
 	 */
 	if (num_online_cpus() > 1 && !running_on_qemu) {
-		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;
-
-			clocksource_cr16.name = "cr16_unstable";
-			clocksource_cr16.flags = CLOCK_SOURCE_UNSTABLE;
-			clocksource_cr16.rating = 0;
-			break;
-		}
+		clocksource_cr16.name = "cr16_unstable";
+		clocksource_cr16.flags = CLOCK_SOURCE_UNSTABLE;
+		clocksource_cr16.rating = 0;
 	}
 
-	/* 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);