Re: [PATCH] cpufreq: intel_pstate: Override parameters if HWP forced by BIOS

From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	Doug Smythies <doug.smythies@gmail.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
	Len Brown <len.brown@intel.com>,
	Doug Smythies <dsmythies@telus.net>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux PM <linux-pm@vger.kernel.org>
Subject: Re: [PATCH] cpufreq: intel_pstate: Override parameters if HWP forced by BIOS
Date: Thu, 9 Sep 2021 13:18:35 +0200	[thread overview]
Message-ID: <CAJZ5v0gn8rpTiVqkXgGqPFDH8-BKTYGiypM-2A2q1jJLm6HbCQ@mail.gmail.com> (raw)
In-Reply-To: <223a72d91cfda9b13230e4f8cd6a29f853535277.camel@linux.intel.com>

On Thu, Sep 9, 2021 at 8:52 AM Srinivas Pandruvada
<srinivas.pandruvada@linux.intel.com> wrote:
>
> On Wed, 2021-09-08 at 20:48 -0700, Doug Smythies wrote:
> > If HWP has been already been enabled by BIOS, it may be
> > necessary to override some kernel command line parameters.
> > Once it has been enabled it requires a reset to be disabled.
> >
> > Signed-off-by: Doug Smythies <dsmythies@telus.net>
> > ---
> >  drivers/cpufreq/intel_pstate.c | 22 ++++++++++++++++------
> >  1 file changed, 16 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/cpufreq/intel_pstate.c
> > b/drivers/cpufreq/intel_pstate.c
> > index bb4549959b11..073bae5d4498 100644
> > --- a/drivers/cpufreq/intel_pstate.c
> > +++ b/drivers/cpufreq/intel_pstate.c
> > @@ -3267,7 +3267,7 @@ static int __init intel_pstate_init(void)
> >                  */
> >                 if ((!no_hwp && boot_cpu_has(X86_FEATURE_HWP_EPP)) ||
> >                     intel_pstate_hwp_is_enabled()) {
> > -                       hwp_active++;
> > +                       hwp_active = 1;
> Why this change?

I think hwp_active can be changed to bool and then it would make sense
to update this line.

> >                         hwp_mode_bdw = id->driver_data;
> >                         intel_pstate.attr = hwp_cpufreq_attrs;
> >                         intel_cpufreq.attr = hwp_cpufreq_attrs;
> > @@ -3347,17 +3347,27 @@ device_initcall(intel_pstate_init);
> >
> >  static int __init intel_pstate_setup(char *str)
> >  {
> > +       /*
> > +        * If BIOS is forcing HWP, then parameter
> > +        * overrides might be needed. Only print
> > +        * the message once, and regardless of
> > +        * any overrides.
> > +        */
> > +       if(!hwp_active
> This part of code is from early_param, Is it possible that
> hwp_active is not 0?

Well, it wouldn't matter even if it were nonzero.  This check is just
pointless anyway.

> > && boot_cpu_has(X86_FEATURE_HWP))
> > +               if(intel_pstate_hwp_is_enabled()){

This should be

if (boot_cpu_has(X86_FEATURE_HWP) && intel_pstate_hwp_is_enabled()) {

> > +                       pr_info("HWP enabled by BIOS\n");
> > +                       hwp_active = 1;
> > +               }
> >         if (!str)
> >                 return -EINVAL;
> >
> > -       if (!strcmp(str, "disable"))
> > +       if (!strcmp(str, "disable") && !hwp_active)
> >                 no_load = 1;
> > -       else if (!strcmp(str, "active"))
> > +       if (!strcmp(str, "active"))
> >                 default_driver = &intel_pstate;
> > -       else if (!strcmp(str, "passive"))
> > +       if (!strcmp(str, "passive"))
> >                 default_driver = &intel_cpufreq;
>
> Why "else if" changed to "if" ?
>
> > -
> > -       if (!strcmp(str, "no_hwp")) {
> > +       if (!strcmp(str, "no_hwp") && !hwp_active) {
> >                 pr_info("HWP disabled\n");
> >                 no_hwp = 1;
> >         }
>