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

From: Rafael J. Wysocki
Date: Thu Sep 09 2021 - 07:19:46 EST


On Thu, Sep 9, 2021 at 8:52 AM Srinivas Pandruvada
<srinivas.pandruvada@xxxxxxxxxxxxxxx> 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@xxxxxxxxx>
> > ---
> > 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;
> > }
>