[PATCH v6 5/6] arm64: add hw_nmi_get_sample_period for preparation of lockup detector

From: Lecopzer Chen <lecopzer.chen@mediatek.com>
To: <linux-arm-kernel@lists.infradead.org>, <linux-kernel@vger.kernel.org>
Cc: <pmladek@suse.com>, <acme@kernel.org>,
	<akpm@linux-foundation.org>, <alexander.shishkin@linux.intel.com>,
	<catalin.marinas@arm.com>, <davem@davemloft.net>,
	<jolsa@redhat.com>, <jthierry@redhat.com>,
	<keescook@chromium.org>, <kernelfans@gmail.com>,
	<lecopzer.chen@mediatek.com>,
	<linux-mediatek@lists.infradead.org>,
	<linux-perf-users@vger.kernel.org>, <mark.rutland@arm.com>,
	<masahiroy@kernel.org>, <matthias.bgg@gmail.com>,
	<maz@kernel.org>, <mcgrof@kernel.org>, <mingo@redhat.com>,
	<namhyung@kernel.org>, <nixiaoming@huawei.com>,
	<peterz@infradead.org>, <sparclinux@vger.kernel.org>,
	<sumit.garg@linaro.org>, <wangqing@vivo.com>, <will@kernel.org>,
	<yj.chiang@mediatek.com>
Subject: [PATCH v6 5/6] arm64: add hw_nmi_get_sample_period for preparation of lockup detector
Date: Tue, 14 Jun 2022 14:28:34 +0800	[thread overview]
Message-ID: <20220614062835.7196-6-lecopzer.chen@mediatek.com> (raw)
In-Reply-To: <20220614062835.7196-1-lecopzer.chen@mediatek.com>

Set safe maximum CPU frequency to 5 GHz in case a particular platform
doesn't implement cpufreq driver.
Although, architecture doesn't put any restrictions on
maximum frequency but 5 GHz seems to be safe maximum given the available
Arm CPUs in the market which are clocked much less than 5 GHz.

On the other hand, we can't make it much higher as it would lead to
a large hard-lockup detection timeout on parts which are running
slower (eg. 1GHz on Developerbox) and doesn't possess a cpufreq driver.

[1]:http://lore.kernel.org/linux-arm-kernel/1610712101-14929-1-git-send-email-sumit.garg@linaro.org

Co-developed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Co-developed-by: Pingfan Liu <kernelfans@gmail.com>
Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
---
 arch/arm64/kernel/Makefile       |  1 +
 arch/arm64/kernel/watchdog_hld.c | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+)
 create mode 100644 arch/arm64/kernel/watchdog_hld.c

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index fa7981d0d917..303b69ad5366 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -46,6 +46,7 @@ obj-$(CONFIG_MODULES)			+= module.o
 obj-$(CONFIG_ARM64_MODULE_PLTS)		+= module-plts.o
 obj-$(CONFIG_PERF_EVENTS)		+= perf_regs.o perf_callchain.o
 obj-$(CONFIG_HW_PERF_EVENTS)		+= perf_event.o
+obj-$(CONFIG_HARDLOCKUP_DETECTOR_PERF)	+= watchdog_hld.o
 obj-$(CONFIG_HAVE_HW_BREAKPOINT)	+= hw_breakpoint.o
 obj-$(CONFIG_CPU_PM)			+= sleep.o suspend.o
 obj-$(CONFIG_CPU_IDLE)			+= cpuidle.o
diff --git a/arch/arm64/kernel/watchdog_hld.c b/arch/arm64/kernel/watchdog_hld.c
new file mode 100644
index 000000000000..de43318e4dd6
--- /dev/null
+++ b/arch/arm64/kernel/watchdog_hld.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/cpufreq.h>
+
+/*
+ * Safe maximum CPU frequency in case a particular platform doesn't implement
+ * cpufreq driver. Although, architecture doesn't put any restrictions on
+ * maximum frequency but 5 GHz seems to be safe maximum given the available
+ * Arm CPUs in the market which are clocked much less than 5 GHz. On the other
+ * hand, we can't make it much higher as it would lead to a large hard-lockup
+ * detection timeout on parts which are running slower (eg. 1GHz on
+ * Developerbox) and doesn't possess a cpufreq driver.
+ */
+#define SAFE_MAX_CPU_FREQ	5000000000UL // 5 GHz
+u64 hw_nmi_get_sample_period(int watchdog_thresh)
+{
+	unsigned int cpu = smp_processor_id();
+	unsigned long max_cpu_freq;
+
+	max_cpu_freq = cpufreq_get_hw_max_freq(cpu) * 1000UL;
+	if (!max_cpu_freq)
+		max_cpu_freq = SAFE_MAX_CPU_FREQ;
+
+	return (u64)max_cpu_freq * watchdog_thresh;
+}
+
-- 
2.25.1

