linux-kernel - Re: [PATCH 1/3] PM: domains: Drop the performance state vote for a device at detach

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Date:   Thu, 9 Sep 2021 16:45:38 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Stephan Gerhold <stephan@...hold.net>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] PM: domains: Drop the performance state vote for a
 device at detach

On Thu, 9 Sept 2021 at 15:48, Dmitry Osipenko <digetx@...il.com> wrote:
>
> 07.09.2021 13:16, Ulf Hansson пишет:
> ...
> >>> Also note that a very similar problem exists, *before* the device gets
> >>> attached in the first place. More precisely, nothing prevents the
> >>> performance state from being set to a non-compatible value for an
> >>> always-on HW/device that hasn't been attached yet. So maybe you need
> >>> to set the maximum performance state at genpd initializations, then
> >>> use the ->sync_state() callback to very that all consumers have been
> >>> attached to the genpd provider, before allowing the state to be
> >>> changed/lowered?
> >>
> >> That is already done by the PD driver.
> >>
> >> https://elixir.bootlin.com/linux/latest/source/drivers/soc/tegra/pmc.c#L3790
> >
> > Yes, I already knew that, but forgot it. :-) Thanks for the pointer.
> > Let me rethink the approach.
> >
> > In a way, it kind of sounds like this is a generic problem - so
> > perhaps we should think of adding a ->withdraw_sync_state() callback
> > that can be assigned by provider drivers, to get informed when a
> > consumer driver is getting unbinded.
>
> Not sure, doesn't feel to me that this is necessary for today. A bit too
> cumbersome for a simple sanity-check, IMO.

Maybe, but I can bring it up with the fw_devlinks people to see what they think.

In any case, we should not move forward with $subject patch as is.

Let me think about it.

Kind regards
Uffe