linux-kernel - Re: [PATCH v3 7/7] clocksource/drivers/arm_arch_timer: validate arch_timer

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Date:   Fri, 14 Feb 2020 01:35:58 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ionela Voinescu <ionela.voinescu@....com>, catalin.marinas@....com,
        will@...nel.org, mark.rutland@....com, maz@...nel.org,
        suzuki.poulose@....com, sudeep.holla@....com, lukasz.luba@....com,
        valentin.schneider@....com, rjw@...ysocki.net,
        ionela.voinescu@....com
Cc:     peterz@...radead.org, mingo@...hat.com, vincent.guittot@...aro.org,
        viresh.kumar@...aro.org, linux-arm-kernel@...ts.infradead.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 7/7] clocksource/drivers/arm_arch_timer: validate arch_timer_rate

Ionela Voinescu <ionela.voinescu@....com> writes:

> From: Valentin Schneider <valentin.schneider@....com>
>
> Using an arch timer with a frequency of less than 1MHz can result in an
> incorrect functionality of the system which assumes a reasonable rate.
>
> One example is the use of activity monitors for frequency invariance
> which uses the rate of the arch timer as the known rate of the constant
> cycle counter in computing its ratio compared to the maximum frequency
> of a CPU. For arch timer frequencies less than 1MHz this ratio could
> end up being 0 which is an invalid value for its use.
>
> Therefore, warn if the arch timer rate is below 1MHz which contravenes
> the recommended architecture interval of 1 to 50MHz.
>
> Signed-off-by: Ionela Voinescu <ionela.voinescu@....com>

So this patch is from Valentin. Where is his Signed-off-by?

>  
> +static int validate_timer_rate(void)
> +{
> +	if (!arch_timer_rate)
> +		return -EINVAL;
> +
> +	/* Arch timer frequency < 1MHz can cause trouble */
> +	WARN_ON(arch_timer_rate < 1000000);

This does not make sense to me. If the rate is out of bounds then why
warn an just continue instead of making it fail?

Thanks,

        tglx