[PATCH v4 16/17] arm64: add hw_nmi_get_sample_period for preparation of lockup detector

[Douglas Anderson]

From: Lecopzer Chen <lecopzer.chen at 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.

Co-developed-by: Sumit Garg <sumit.garg at linaro.org>
Signed-off-by: Sumit Garg <sumit.garg at linaro.org>
Co-developed-by: Pingfan Liu <kernelfans at gmail.com>
Signed-off-by: Pingfan Liu <kernelfans at gmail.com>
Signed-off-by: Lecopzer Chen <lecopzer.chen at mediatek.com>
Signed-off-by: Douglas Anderson <dianders at chromium.org>
---
I yanked this patch from the mailing lists [1] into my series just to
make it easier to avoid conflicts between my series and the one adding
the arm64 perf hardlockup detector, in case someone wanted to test
them both together.

The only change I made here was to remove an extra blank line that
checkpatch complained about.

As mentioned in the cover letter, I'm not really expecting this patch
to land together with the patches for the buddy detector. I included
it with my series simply for convenience of testing both series
together.

NOTE: the previous patch posted by Lecopzer pointed to Sumit's
patch [2] in the commit text but provided no context. I moved it to
this "after the cut" note.

[1] https://lore.kernel.org/r/20220903093415.15850-6-lecopzer.chen@mediatek.com/
[2] http://lore.kernel.org/linux-arm-kernel/1610712101-14929-1-git-send-email-sumit.garg@linaro.org

Changes in v4:
- Pulled ("add hw_nmi_get_sample_period for ...") into my series for v4.

 arch/arm64/kernel/Makefile       |  1 +
 arch/arm64/kernel/watchdog_hld.c | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 arch/arm64/kernel/watchdog_hld.c

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index ceba6792f5b3..f8e2645406a4 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..2401eb1b7e55
--- /dev/null
+++ b/arch/arm64/kernel/watchdog_hld.c
@@ -0,0 +1,24 @@
+// 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;
+}
-- 
2.40.1.521.gf1e218fcd8-goog