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Subject: Re: [PATCH v13 06/35] clk: tegra: Support runtime PM and power domain
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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        Nishanth Menon <nm@ti.com>,
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        Michael Turquette <mturquette@baylibre.com>,
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From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <b06bf794-b8b3-417b-58ef-4d815ca86c95@gmail.com>
Date:   Thu, 7 Oct 2021 00:14:29 +0300
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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.