linux-kernel - Re: [PATCH v13 06/35] clk: tegra: Support runtime PM and power domain

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Date:   Thu, 7 Oct 2021 01:01:37 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Viresh Kumar <vireshk@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Peter Chen <peter.chen@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Nishanth Menon <nm@...com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Michael Turquette <mturquette@...libre.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        linux-staging@...ts.linux.dev, linux-pwm@...r.kernel.org,
        linux-mmc <linux-mmc@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Vignesh Raghavendra <vigneshr@...com>,
        Richard Weinberger <richard@....at>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Lucas Stach <dev@...xeye.de>, Stefan Agner <stefan@...er.ch>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        David Heidelberg <david@...t.cz>
Subject: Re: [PATCH v13 06/35] clk: tegra: Support runtime PM and power domain

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@...il.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.