linux-kernel - Re: [PATCH] intel_idle: Add Comet Lake support

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Date:   Thu, 27 Feb 2020 11:56:51 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Harry Pan <harry.pan@...el.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, Harry Pan <gs0622@...il.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] intel_idle: Add Comet Lake support

On Wed, Feb 26, 2020 at 10:47 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Wed, Feb 26, 2020 at 6:34 PM Harry Pan <harry.pan@...el.com> wrote:
> >
> > Add Comet Lake ID to enable intel_idle driver support.
> > This is required for PC10 and S0ix.
>
> That shouldn't be the case for Linux 5.6-rc as long as the ACPI tables
> expose C10 in _CST, so have you checked that?

Regardless of that (which only is about the changelog), I wouldn't
just use idle_cpu_skl directly for CML like in the patch below.

Instead, I'd define something like

static const struct idle_cpu idle_cpu_cml __initconst = {
    .state_table = skl_cstates,
    .disable_promotion_to_c1e = true,
    .use_acpi = true,
};

and point  to it from the CML entries in intel_idle_ids[].

That would allow the driver to avoid enabling the C-states that are
not exposed in the ACPI tables by default which generally is safer
than exposing all of them for all CML platforms unconditionally.

> > Signed-off-by: Harry Pan <harry.pan@...el.com>
> >
> > ---
> >
> >  drivers/idle/intel_idle.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> > index 347b08b56042..3cf292b2b7f1 100644
> > --- a/drivers/idle/intel_idle.c
> > +++ b/drivers/idle/intel_idle.c
> > @@ -1086,6 +1086,8 @@ static const struct x86_cpu_id intel_idle_ids[] __initconst = {
> >         INTEL_CPU_FAM6(KABYLAKE_L,              idle_cpu_skl),
> >         INTEL_CPU_FAM6(KABYLAKE,                idle_cpu_skl),
> >         INTEL_CPU_FAM6(SKYLAKE_X,               idle_cpu_skx),
> > +       INTEL_CPU_FAM6(COMETLAKE_L,             idle_cpu_skl),
> > +       INTEL_CPU_FAM6(COMETLAKE,               idle_cpu_skl),

+       INTEL_CPU_FAM6(COMETLAKE_L,             idle_cpu_cml),
+       INTEL_CPU_FAM6(COMETLAKE,               idle_cpu_cml),

> >         INTEL_CPU_FAM6(XEON_PHI_KNL,            idle_cpu_knl),
> >         INTEL_CPU_FAM6(XEON_PHI_KNM,            idle_cpu_knl),
> >         INTEL_CPU_FAM6(ATOM_GOLDMONT,           idle_cpu_bxt),
> > --
> > 2.24.1
> >