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From:   Dragan Mladjenovic <Dragan.Mladjenovic@syrmia.com>
To:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc:     Chao-ying Fu <cfu@wavecomp.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Greg Ungerer <gerg@kernel.org>,
        Hauke Mehrtens <hauke@hauke-m.de>,
        Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org,
        Marc Zyngier <maz@kernel.org>,
        Paul Burton <paulburton@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Serge Semin <fancer.lancer@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tiezhu Yang <yangtiezhu@loongson.cn>,
        Dragan Mladjenovic <dragan.mladjenovic@syrmia.com>
Subject: [PATCH v2 08/12] clocksource: mips-gic-timer: Enable counter when CPUs start
Date:   Wed, 25 May 2022 14:10:26 +0200
Message-Id: <20220525121030.16054-9-Dragan.Mladjenovic@syrmia.com>
In-Reply-To: <20220525121030.16054-1-Dragan.Mladjenovic@syrmia.com>
References: <20220525121030.16054-1-Dragan.Mladjenovic@syrmia.com>
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From: Paul Burton <paulburton@kernel.org>

In multi-cluster MIPS I6500 systems we have a GIC in each cluster, each
with its own counter. When a cluster powers up the counter will be
stopped, with the COUNTSTOP bit set in the GIC_CONFIG register.

In single cluster systems it has been fine for us to clear COUNTSTOP
once in gic_clocksource_of_init() in order to start the counter, since
with only one cluster we know that we won't be resetting that cluster's
GIC at any point (ignoring suspend/resume cycles which would need to
handle clearing COUNTSTOP in the resume path). Once we support
multi-cluster systems this will only have started the counter in the
boot cluster, and any CPUs in other clusters will find their counter
stopped which will break the GIC clock_event_device.

Resolve this by having CPUs clear the COUNTSTOP bit when they come
online, using the existing gic_starting_cpu() CPU hotplug callback. This
will allow CPUs in secondary clusters to ensure that the cluster's GIC
counter is running as expected.

Signed-off-by: Paul Burton <paulburton@kernel.org>
Signed-off-by: Chao-ying Fu <cfu@wavecomp.com>
Signed-off-by: Dragan Mladjenovic <dragan.mladjenovic@syrmia.com>

diff --git a/drivers/clocksource/mips-gic-timer.c b/drivers/clocksource/mips-gic-timer.c
index 6632d314a2c0..90a736a13115 100644
--- a/drivers/clocksource/mips-gic-timer.c
+++ b/drivers/clocksource/mips-gic-timer.c
@@ -119,6 +119,9 @@ static void gic_update_frequency(void *data)
 
 static int gic_starting_cpu(unsigned int cpu)
 {
+	/* Ensure the GIC counter is running */
+	clear_gic_config(GIC_CONFIG_COUNTSTOP);
+
 	gic_clockevent_cpu_init(cpu, this_cpu_ptr(&gic_clockevent_device));
 	return 0;
 }
@@ -289,9 +292,6 @@ static int __init gic_clocksource_of_init(struct device_node *node)
 			pr_warn("Unable to register clock notifier\n");
 	}
 
-	/* And finally start the counter */
-	clear_gic_config(GIC_CONFIG_COUNTSTOP);
-
 	/*
 	 * It's safe to use the MIPS GIC timer as a sched clock source only if
 	 * its ticks are stable, which is true on either the platforms with
-- 
2.17.1