linux-kernel - Re: [PATCH v8 3/4] intel_idle: Provide the default enter

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Message-ID: <CAJZ5v0hL0QOT17DnsUKONHVy1+Yy84soPWU74gHAxjsozerPgg@mail.gmail.com>
Date: Tue, 10 Dec 2024 21:26:16 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, 
	rafael.j.wysocki@...el.com, peterz@...radead.org, dave.hansen@...ux.intel.com, 
	gautham.shenoy@....com, tglx@...utronix.de, len.brown@...el.com, 
	artem.bityutskiy@...ux.intel.com
Subject: Re: [PATCH v8 3/4] intel_idle: Provide the default enter_dead() handler

On Wed, Dec 4, 2024 at 3:08 PM Patryk Wlazlyn
<patryk.wlazlyn@...ux.intel.com> wrote:
>
> Recent Intel platforms require idle driver to provide information about
> the MWAIT hint used to enter the deepest idle state in the play_dead
> code.
>
> Provide the default enter_dead() handler for all of the platforms and
> allow overwriting with a custom handler for each platform if needed.

My changelog for this patch:

"A subsequent change is going to make native_play_dead() rely on the
idle driver to put CPUs going offline into appropriate idle states.

For this reason, provide the default :enter_dead() handler for all of
the idle states on all platforms supported by intel_idle with an
option to override it with a custom handler if needed."

> Signed-off-by: Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>
> ---
>  drivers/idle/intel_idle.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> index ac4d8faa3886..c6874a6dbe95 100644
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -56,6 +56,7 @@
>  #include <asm/mwait.h>
>  #include <asm/spec-ctrl.h>
>  #include <asm/fpu/api.h>
> +#include <asm/smp.h>
>
>  #define INTEL_IDLE_VERSION "0.5.1"
>
> @@ -227,6 +228,16 @@ static __cpuidle int intel_idle_s2idle(struct cpuidle_device *dev,
>         return 0;
>  }
>
> +static __cpuidle void intel_idle_enter_dead(struct cpuidle_device *dev,
> +                                           int index)
> +{
> +       struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
> +       struct cpuidle_state *state = &drv->states[index];
> +       unsigned long eax = flg2MWAIT(state->flags);
> +
> +       mwait_play_dead(eax);
> +}
> +
>  /*
>   * States are indexed by the cstate number,
>   * which is also the index into the MWAIT hint array.
> @@ -1798,6 +1809,7 @@ static void __init intel_idle_init_cstates_acpi(struct cpuidle_driver *drv)
>                         state->flags |= CPUIDLE_FLAG_TIMER_STOP;
>
>                 state->enter = intel_idle;
> +               state->enter_dead = intel_idle_enter_dead;
>                 state->enter_s2idle = intel_idle_s2idle;
>         }
>  }
> @@ -2143,10 +2155,12 @@ static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv)
>                 if (intel_idle_max_cstate_reached(cstate))
>                         break;
>
> -               if (!cpuidle_state_table[cstate].enter &&
> -                   !cpuidle_state_table[cstate].enter_s2idle)
> +               if (!cpuidle_state_table[cstate].enter)

I don't think that the above change belongs to this patch.  If I'm
mistaken, it should be mentioned in the changelog and the reason for
making it should be explained.

>                         break;
>
> +               if (!cpuidle_state_table[cstate].enter_dead)
> +                       cpuidle_state_table[cstate].enter_dead = intel_idle_enter_dead;
> +
>                 /* If marked as unusable, skip this state. */
>                 if (cpuidle_state_table[cstate].flags & CPUIDLE_FLAG_UNUSABLE) {
>                         pr_debug("state %s is disabled\n",
> --