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

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Date:   Tue, 30 Nov 2021 05:45:10 -0800
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "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>,
        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>,
        "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 3/7] thermal: intel: hfi: Minimally initialize the
 Hardware Feedback Interface

On Mon, Nov 29, 2021 at 07:55:18PM -0800, Srinivas Pandruvada wrote:
> On Mon, 2021-11-29 at 19:20 -0800, Ricardo Neri wrote:
> > On Wed, Nov 24, 2021 at 03:09:20PM +0100, Rafael J. Wysocki wrote:
> > > On Sat, Nov 6, 2021 at 2:34 AM 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 individual HFI
> > > > tables.
> > > > 
> > > > A subsequent changeset will provide per-CPU initialization and
> > > > interrupt
> > > > handling.
> > > > 
> 
> [...]
> 
> > > > +       /*
> > > > +        * If we are here we know that CPUID_HFI_LEAF exists.
> > > > Parse the
> > > > +        * supported capabilities and the size of the HFI table.
> > > > +        */
> > > > +       reg = cpuid_edx(CPUID_HFI_LEAF);
> > > > +
> > > > +       hfi_features.capabilities = reg & HFI_CAPABILITIES_MASK;
> > > > +       if (!(hfi_features.capabilities &
> > > > HFI_CAPABILITIES_PERFORMANCE)) {
> > > > +               pr_err("Performance reporting not supported! Not
> > > > using HFI\n");
> > > 
> > > This doesn't need to be pr_err().
> > 
> > Should it be a pr_warn() or perhaps pr_info()?
> May be even pr_debug as we can always enable dynamic debug, where we
> need to debug.

Fair enough. That sounds good. I will make the change.

Thanks and BR,
Ricardo