linux-kernel - Re: ACPI support in common clock framework

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Date:   Fri, 15 Jun 2018 10:43:11 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Srinath Mannam <srinath.mannam@...adcom.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-clk <linux-clk@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: ACPI support in common clock framework

Quoting Rafael J. Wysocki (2018-06-13 01:27:39)
> On Wed, Jun 13, 2018 at 10:13 AM, Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > +Cc: Rafael, ACPI ML
> >
> > On Wed, Jun 13, 2018 at 7:14 AM, Srinath Mannam
> > <srinath.mannam@...adcom.com> wrote:
> >> Hi Michael, Stephen,
> >>
> >> We are adding ACPI support in our Linux based platform.
> >> At present our clock hierarchy using common clock framework through DTS.
> >> Now we required ACPI support in common clock framework to upgrade our platform.
> >>
> >> For example, clk_get API called in many drivers to get clock device is
> >> tightly coupled with DT framework.
> >>
> >> Please let us know, if anybody in Open Source community have plans to
> >> add ACPI support for common clock framework.
> 
> There are no plans for doing that AFAICS.
> 
> Moreover, it generally would not be consistent with ACPI power
> management defined by the specification.

This matches my understanding.

> 
> >> If not please suggest us alternative method to use common clock
> >> framework in ACPI use case.
> 
> The problem with using the clock framework on systems with ACPI is
> that, in general, the clock manipulation is expected to be carried out
> by ACPI power management and therefore it is "owned" by AML.
> Currently, there are no defined methods for synchronizing the AML's
> use of clocks for power management with what the OS may do with them
> directly.
> 
> In theory, that can be worked around to some extent by representing
> clocks as power resources in ASL (even though the provider information
> would be missing then) and manipulating those power resources directly
> from the OS.  I'm not aware of anyone doing that successfully,
> however.
> 
> For simple power management it should be sufficient to let drivers
> rely on the ACPI PM domain which should happen automatically in the
> majority of cases anyway.
> 

Is this for clk_enable/disable? What about clk_set_rate() or
clk_set_phase()? Is ACPI's AML taking care of that?