From: Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
To: Viresh Kumar <viresh.kumar-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Cc: Thierry Reding
<thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
"Rafael J . Wysocki"
<rjw-LthD3rsA81gm4RdzfppkhA@public.gmane.org>,
linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 1/2] cpufreq: tegra186: Fix initial frequency
Date: Tue, 14 Jul 2020 08:26:39 +0100 [thread overview]
Message-ID: <aa941c67-1dec-5363-7bd7-5e9d8d324110@nvidia.com> (raw)
In-Reply-To: <20200714034635.2zdv3wzmftjg2t4a@vireshk-i7>
On 14/07/2020 04:46, Viresh Kumar wrote:
> On 13-07-20, 17:37, Jon Hunter wrote:
>>
>> 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.
>
> The get() callback is supposed to read the frequency from hardware and
> return it, no cached value here. policy->cur may end up being wrong in
> case there is a bug.
OK, I can add a get callback. However, there are a few other drivers
that set the current frequency in the init() and don't implement a get()
callback ...
drivers/cpufreq/pasemi-cpufreq.c
drivers/cpufreq/ppc_cbe_cpufreq.c
drivers/cpufreq/intel_pstate.c
Jon
--
nvpublic
next prev parent reply other threads:[~2020-07-14 7:26 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-12 10:06 [PATCH 1/2] cpufreq: tegra186: Fix initial frequency Jon Hunter
[not found] ` <20200712100645.13927-1-jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2020-07-12 10:06 ` [PATCH 2/2] cpufreq: tegra186: Simplify probe return path Jon Hunter
[not found] ` <20200712100645.13927-2-jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2020-07-13 3:28 ` Viresh Kumar
2020-07-13 3:25 ` [PATCH 1/2] cpufreq: tegra186: Fix initial frequency Viresh Kumar
2020-07-13 16:37 ` Jon Hunter
[not found] ` <3d6091f2-6b04-185f-6c23-e39a34b87877-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2020-07-14 3:46 ` Viresh Kumar
2020-07-14 7:26 ` Jon Hunter [this message]
[not found] ` <aa941c67-1dec-5363-7bd7-5e9d8d324110-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2020-07-14 7:31 ` Viresh Kumar
2020-07-31 12:14 ` Jon Hunter
2020-08-04 5:25 ` Viresh Kumar
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