linux-kernel - Re: [PATCH v2 3/7] thermal: intel: hfi: Minimally initialize the Hardware Feedback Interface

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Date:   Sun, 2 Jan 2022 13:46:47 -0800
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Len Brown <len.brown@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Amit Kucheria <amitk@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Lukasz Luba <lukasz.luba@....com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/7] thermal: intel: hfi: Minimally initialize the
 Hardware Feedback Interface

On Thu, Dec 30, 2021 at 07:43:22PM +0100, Rafael J. Wysocki wrote:
> On Mon, Dec 20, 2021 at 4:23 PM Ricardo Neri
> <ricardo.neri-calderon@...ux.intel.com> wrote:
> >
> > The Intel Hardware Feedback Interface provides guidance to the operating
> > system about the performance and energy efficiency capabilities of each
> > CPU in the system. Capabilities are numbers between 0 and 255 where a
> > higher number represents a higher capability. For each CPU, energy
> > efficiency and performance are reported as separate capabilities.
> >
> > Hardware computes these capabilities based on the operating conditions of
> > the system such as power and thermal limits. These capabilities are shared
> > with the operating system in a table resident in memory. Each package in
> > the system has its own HFI instance. Every logical CPU in the package is
> > represented in the table. More than one logical CPUs may be represented in
> > a single table entry. When the hardware updates the table, it generates a
> > package-level thermal interrupt.
> >
> > The size and format of the HFI table depend on the supported features and
> > can only be determined at runtime. To minimally initialize the HFI, parse
> > its features and allocate one instance per package of a data structure with
> > the necessary parameters to read and navigate a local copy (i.e., owned by
> > the driver) of individual HFI tables.
> >
> > A subsequent changeset will provide per-CPU initialization and interrupt
> > handling.
> >
> > Cc: Andi Kleen <ak@...ux.intel.com>
> > Cc: Aubrey Li <aubrey.li@...ux.intel.com>
> > Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> > Cc: Tim Chen <tim.c.chen@...ux.intel.com>
> > Cc: "Ravi V. Shankar" <ravi.v.shankar@...el.com>
> > Reviewed-by: Len Brown <len.brown@...el.com>
> > Co-developed by: Aubrey Li <aubrey.li@...ux.intel.com>
> > Signed-off-by: Aubrey Li <aubrey.li@...ux.intel.com>
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> > ---
> > Changes since v1:
> >   * Renamed X86_FEATURE_INTEL_HFI as X86_FEATURE_HFI. (Boris)
> >   * Reworked parsing of HFI features using bitfields instead of bitmasks.
> >     (PeterZ).
> >   * Removed hfi_instance::parsed as hfi_parse_features() is called only
> >     once via intel_hfi_init() via thermal_throttle_init_device().
> >     (Rafael)
> >   * Converted pr_err() to pr_debug(). (Srinivas, Rafael)
> >   * Removed unnecessary dependency on CONFIG_SCHED_MC.
> >   * Renamed hfi_instance::ts_counter as hfi_instance::timestamp.
> >   * Renamed hfi_instance::table_base as hfi_instance::local_table and
> >     relocated its definition to this patch.
> >   * Wrapped hfi_instance::timestamp and hfi_instance:local_table in an
> >     anonymous union, since both point at the same location.
> > ---
> >  drivers/thermal/intel/Kconfig       |  12 ++
> >  drivers/thermal/intel/Makefile      |   1 +
> >  drivers/thermal/intel/intel_hfi.c   | 175 ++++++++++++++++++++++++++++
> >  drivers/thermal/intel/intel_hfi.h   |  11 ++
> >  drivers/thermal/intel/therm_throt.c |   3 +
> >  5 files changed, 202 insertions(+)
> >  create mode 100644 drivers/thermal/intel/intel_hfi.c
> >  create mode 100644 drivers/thermal/intel/intel_hfi.h
> >
> > diff --git a/drivers/thermal/intel/Kconfig b/drivers/thermal/intel/Kconfig
> > index c83ea5d04a1d..1a21ff60fdc7 100644
> > --- a/drivers/thermal/intel/Kconfig
> > +++ b/drivers/thermal/intel/Kconfig
> > @@ -99,3 +99,15 @@ config INTEL_MENLOW
> >           Intel Menlow platform.
> >
> >           If unsure, say N.
> > +
> > +config INTEL_HFI
> 
> This looks like it may be too general, because HFI is not a thermal-only thing.

> 
> Maybe cal it INTEL_HFI_THERMAL?

True. The *Enhanced* HFI introduces the concept of thread classes [1]. I was
planning to wrap this patchset, which parses the HFI table and deals
with updates, as INTEL_HFI. The code that deals with classes would be
wrapped as INTEL_EHFI.

After this comment, so you still think that INTEL_HFI_THERMAL makes more
sense?

Thanks and BR,
Ricardo


[1]. https://www.intel.com/content/www/us/en/develop/download/intel-architecture-instruction-set-extensions-programming-reference.html , Chapter 13