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

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Message-ID: <9a463228ef9f668618a4d1470eb9925f8d332465.camel@linux.intel.com>
Date:   Mon, 29 Nov 2021 19:55:18 -0800
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        "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>,
        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, 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.

Thanks,
Srinivas

> 
> Thanks and BR,
> Ricardo
>