linux-kernel - Re: [PATCH v4 1/2] watchdog: move arm64 watchdog

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Message-ID: <aQixsIQXTjYyhRVj@willie-the-truck>
Date: Mon, 3 Nov 2025 13:44:16 +0000
From: Will Deacon <will@...nel.org>
To: Yunhui Cui <cuiyunhui@...edance.com>
Cc: akpm@...ux-foundation.org, alex@...ti.fr, anup@...infault.org,
	aou@...s.berkeley.edu, atish.patra@...ux.dev,
	catalin.marinas@....com, dianders@...omium.org,
	johannes@...solutions.net, lihuafei1@...wei.com,
	mark.rutland@....com, masahiroy@...nel.org, maz@...nel.org,
	mingo@...nel.org, nicolas.schier@...ux.dev, palmer@...belt.com,
	paul.walmsley@...ive.com, suzuki.poulose@....com,
	thorsten.blum@...ux.dev, wangjinchao600@...il.com,
	yangyicong@...ilicon.com, zhanjie9@...ilicon.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v4 1/2] watchdog: move arm64 watchdog_hld into common code

On Tue, Oct 14, 2025 at 11:14:24AM +0800, Yunhui Cui wrote:
> @@ -306,3 +307,85 @@ void __init hardlockup_config_perf_event(const char *str)
>  	wd_hw_attr.type = PERF_TYPE_RAW;
>  	wd_hw_attr.config = config;
>  }
> +
> +#ifdef CONFIG_WATCHDOG_PERF_ADJUST_PERIOD
> +/*
> + * 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
> + * 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
> +__weak 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;
> +}

Why does this function become __weak? Neither arm64 nor riscv override
it afaict.

Will