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

[Ulf Hansson <ulf.hansson@linaro.org>]

On Thu, 7 Oct 2021 at 01:21, Dmitry Osipenko <digetx@gmail.com> wrote:
>
> 07.10.2021 01:01, Dmitry Osipenko пишет:
> > 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.
> >
>
> Please let me iterate once again. The problem we currently have is that
> clock may be enabled during NOIRQ time. In order to enable clock, it
> needs to be prepared. In order to prepare clock, the clock's device
> needs to be runtime-resumed. The runtime PM is unavailable at the NOIRQ
> time.
>
> To solve this problem we need to prepare clock beforehand.
>
> The clock will stay prepared during suspend, but this is not a problem
> since all the clocks we care about don't require high voltage and
> voltage is guaranteed to be bumped high during suspend by Tegra's
> regulator-coupler driver anyways.
>
> So everything we need to do is to keep clocks prepared. There are two
> options how to do that:
>
> [1] this patch which explicitly prepares clocks using clk API.
>
> [2] Use runtime PM API, like this:
>
> static const struct dev_pm_ops tegra_clock_pm = {
>         SET_SYSTEM_SLEEP_PM_OPS(pm_runtime_resume_and_get, pm_runtime_put)
> };
>
> Ulf, are you now okay with the current variant [1] of the patch or you
> prefer the second [2] option more?

I prefer option [2]. The clock_prepare|unprepare() thingy in option
[1], looks more like an odd workaround to me.

Does that make sense to you as well?

Kind regards
Uffe