linux-kernel - Re: [PATCH 1/2] cpufreq: tegra186: Fix initial frequency

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Message-ID: <3d6091f2-6b04-185f-6c23-e39a34b87877@nvidia.com>
Date:   Mon, 13 Jul 2020 17:37:36 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
CC:     Thierry Reding <thierry.reding@...il.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] cpufreq: tegra186: Fix initial frequency


On 13/07/2020 04:25, Viresh Kumar wrote:
> On 12-07-20, 11:06, Jon Hunter wrote:
>> Commit 6cc3d0e9a097 ("cpufreq: tegra186: add
>> CPUFREQ_NEED_INITIAL_FREQ_CHECK flag") fixed CPUFREQ support for
>> Tegra186 but as a consequence the following warnings are now seen on
>> boot ...
>>
>>  cpufreq: cpufreq_online: CPU0: Running at unlisted freq: 0 KHz
>>  cpufreq: cpufreq_online: CPU0: Unlisted initial frequency changed to: 2035200 KHz
>>  cpufreq: cpufreq_online: CPU1: Running at unlisted freq: 0 KHz
>>  cpufreq: cpufreq_online: CPU1: Unlisted initial frequency changed to: 2035200 KHz
>>  cpufreq: cpufreq_online: CPU2: Running at unlisted freq: 0 KHz
>>  cpufreq: cpufreq_online: CPU2: Unlisted initial frequency changed to: 2035200 KHz
>>  cpufreq: cpufreq_online: CPU3: Running at unlisted freq: 0 KHz
>>  cpufreq: cpufreq_online: CPU3: Unlisted initial frequency changed to: 2035200 KHz
>>  cpufreq: cpufreq_online: CPU4: Running at unlisted freq: 0 KHz
>>  cpufreq: cpufreq_online: CPU4: Unlisted initial frequency changed to: 2035200 KHz
>>  cpufreq: cpufreq_online: CPU5: Running at unlisted freq: 0 KHz
>>  cpufreq: cpufreq_online: CPU5: Unlisted initial frequency changed to: 2035200 KHz
>>
>> Although we could fix this by adding a 'get' operator for the Tegra186
>> CPUFREQ driver, there is really little point because the CPUFREQ on
>> Tegra186 is set by writing a value stored in the frequency table to a
>> register and we just need to set the initial frequency.
> 
> The hardware still runs at the frequency requested by cpufreq core here, right ?

Yes.

> It is better to provide the get() callback as it is also used to show the
> current frequency in userspace.

I looked at that and I saw that if the get() callback is not provided,
the current frequency showed by userspace is policy->cur. For this
device, policy->cur is accurate and so if we added the get() callback we
essentially just going to return policy->cur. Therefore, given that we
already know policy->cur, I did not see the point in adding a device
specific handler to do the same thing.

Cheers
Jon

-- 
nvpublic