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Subject: Re: [PATCH v13 06/35] clk: tegra: Support runtime PM and power domain
From:   Dmitry Osipenko <digetx@gmail.com>
To:     Ulf Hansson <ulf.hansson@linaro.org>
Cc:     Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Viresh Kumar <vireshk@kernel.org>,
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        Michael Turquette <mturquette@baylibre.com>,
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Date:   Thu, 7 Oct 2021 01:01:37 +0300
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07.10.2021 00:14, Dmitry Osipenko пишет:
> 06.10.2021 15:43, Ulf Hansson пишет:
>> On Wed, 6 Oct 2021 at 00:43, Dmitry Osipenko <digetx@gmail.com> wrote:
>>>
>>> 06.10.2021 01:19, Dmitry Osipenko пишет:
>>> ...
>>>> I reproduced the OFF problem by removing the clk prepare/unprepare from
>>>> the suspend/resume of the clk driver and making some extra changes to
>>>> clock tree topology and etc to trigger the problem on Nexus 7.
>>>>
>>>> tegra-pmc 7000e400.pmc: failed to turn off PM domain heg: -13
>>>>
>>>> It happens from genpd_suspend_noirq() -> tegra_genpd_power_off() -> clk
>>>> -> GENPD -> I2C -> runtime-pm.
>>>>
>>>> -13 is EACCES, it comes from the runtime PM of I2C device. RPM is
>>>> prohibited/disabled during late (NOIRQ) suspend by the drivers core.
>>>
>>> My bad, I double-checked and it's not I2C RPM that is failing now, but
>>> the clock's RPM [1], which is also unavailable during NOIRQ.
>>
>> Yes, that sounds reasonable.
>>
>> You would then need a similar patch for the tegra clock driver as I
>> suggested for tegra I2C driver. That should solve the problem, I
>> think.
>>
>>>
>>> [1]
>>> https://elixir.free-electrons.com/linux/v5.15-rc4/source/drivers/clk/clk.c#L116
>>>
>>> Previously it was I2C RPM that was failing in a similar way, but code
>>> changed a tad since that time.
>>
>> Alright. In any case, as long as the devices gets suspended in the
>> correct order, I think it should be fine to cook a patch along the
>> lines of what I suggest for the I2C driver as well.
>>
>> It should work, I think. Although, maybe you want to avoid runtime
>> resuming the I2C device, unless it's the device belonging to the PMIC
>> interface, if there is a way to distinguish that for the driver.
> 
> Ulf, thank you very much for the suggestions! I was thinking about this
> all once again and concluded that the simplest variant will be to just
> remove the suspend ops from the clk driver since neither of PLLs require
> high voltage. We now have voltage bumped to a nominal level during
> suspend by Tegra's regulator-coupler driver and it's much higher than
> voltage needed by PLLs. So the problem I was trying to work around
> doesn't really exist anymore.

I hurried a bit with the conclusion, keep forgetting that I need to
change the clock tree in order to test it all properly :/ It's not fixed
yet.