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Date: Mon, 27 May 2024 14:31:29 +0200
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Subject: Re: [PATCH v4 08/14] clocksource: mips-gic-timer: Enable counter when
 CPUs start
To: Aleksandar Rikalo <aleksandar.rikalo@syrmia.com>,
 Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Aleksandar Rikalo <arikalo@gmail.com>, 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>
References: <20240511104341.151550-1-aleksandar.rikalo@syrmia.com>
 <20240511104341.151550-9-aleksandar.rikalo@syrmia.com>
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From: =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= <philmd@linaro.org>
In-Reply-To: <20240511104341.151550-9-aleksandar.rikalo@syrmia.com>
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On 11/5/24 12:43, Aleksandar Rikalo wrote:
> 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>
> Signed-off-by: Aleksandar Rikalo <aleksandar.rikalo@syrmia.com>
> ---
>   drivers/clocksource/mips-gic-timer.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>