linux-kernel - Re: [Patch 2/2] cpufreq: tegra194: Fix unlisted boot freq warning

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Message-ID: <7e285f41-e1ae-e352-9d1b-efd4d20ddfa3@nvidia.com>
Date:   Thu, 8 Oct 2020 16:41:06 +0530
From:   Sumit Gupta <sumitg@...dia.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
CC:     <rjw@...ysocki.net>, <thierry.reding@...il.com>,
        <jonathanh@...dia.com>, <linux-pm@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <ksitaraman@...dia.com>,
        <bbasu@...dia.com>, Sumit Gupta <sumitg@...dia.com>
Subject: Re: [Patch 2/2] cpufreq: tegra194: Fix unlisted boot freq warning

>>
>>>> Warning coming during boot because the boot freq set by bootloader
>>>> gets filtered out due to big freq steps while creating freq_table.
>>>> Fixing this by setting closest ndiv value from freq_table.
>>>> Warning:
>>>>     cpufreq: cpufreq_online: CPU0: Running at unlisted freq
>>>>     cpufreq: cpufreq_online: CPU0: Unlisted initial frequency changed
>>>>
>>>> Also, added change in init to wait till current frequency becomes
>>>> equal or near to the previously requested frequency. This is done
>>>> because it takes some time to restore the previous frequency while
>>>> turning-on non-boot cores during exit from SC7(Suspend-to-RAM).
>>>
>>> So you are trying to figure if the frequency is listed in freq-table or not,
>>> otherwise setting the frequency to a value you think is appropriate. Right ?
>> During boot, want to set the frequency from freq_table which is closest to
>> the one set by bootloader.
> 
> Right.
> 
>> During resume from suspend-to-idle, want to restore the frequency which was
>> set on non-boot cores before they were hotplug powered off.
> 
> Why exactly do you want to do that ? Rather you should provide
> online/offline hooks for the cpufreq driver and do light-weight
> suspend/resume as is done by cpufreq-dt.c as well.
> 
Thank you for pointer. Added online hook to avoid warning during 
hot-plug-on for the non-boot CPU's while exiting from Suspend-to-RAM. Will
send new version with the changes.

>>>
>>> This is what the cpufreq core already does when it printed these boot time
>>> messages. Do we really need to add this much code in here ?
>> We want to avoid the warning messages.
> 
> Hmm, okay.
> 
>>>
>>> If you really don't want to see the warning, how about fixing it the way cpufreq
>>> core does ? i.e. with this call:
>>>
>>> ret = __cpufreq_driver_target(policy, policy->cur - 1, CPUFREQ_RELATION_L);
>>>
>> The cpufreq core change will help in bootup case but not during the case of
>> resume.
>> In this change, reading the previously stored value and restoring it will
>> also fix the warning message during resume.
> 
> You were getting the message during resume as well ? Why ? The
> firmware is updating the frequency to a previous value ? If that is
> so, you should just set the frequency again to some other value during
> resume to fix it.
Yes, it boots at a predefined frequency and then some time is taken to 
restore the last frequency which software requested before entering 
Suspend-to-RAM. We don't need to re-write the register again.

> 
> --
> viresh
>