linux-kernel - Re: [TEGRA194_CPUFREQ Patch v2 2/3] cpufreq: Add Tegra194 cpufreq driver

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Date:   Tue, 7 Apr 2020 22:12:00 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     sumitg <sumitg@...dia.com>, rjw@...ysocki.net,
        viresh.kumar@...aro.org, catalin.marinas@....com, will@...nel.org,
        thierry.reding@...il.com, jonathanh@...dia.com, talho@...dia.com,
        linux-pm@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     bbasu@...dia.com, mperttunen@...dia.com
Subject: Re: [TEGRA194_CPUFREQ Patch v2 2/3] cpufreq: Add Tegra194 cpufreq
 driver

07.04.2020 21:55, sumitg пишет:
...
>>> + * Returns freq in KHz on success, 0 if cpu is offline
>>
>> I don't see any checks in the code about whether CPU is offline.
>>
>> Googling for "queue_work_on offline cpu" suggests that this function
>> should hang.
>>
> Tried this and didn't get crash or hang.
> show_cpuinfo_cur_freq() returns "<unknown>" value on reading frequency
> from a cluster having both it's cores offline.
> If only one cpu is offline, then frequency of other online cpu which is
> managing the policy of that cluster is returned.
> Have still added below check as guard in get|set() freq calls.
>     if (!cpu_online(cpu))
>         return -EINVAL;
> Thankyou for the input.

If CPUFreq core takes care of taking into account the offline CPU, then
the check isn't needed. It also wouldn't be enough if there was a
problem here.