linux-kernel - Re: [RFC PATCH v4 6/8] intel_idle: Provide enter

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Message-ID: <CAJZ5v0gpSCWMLxekbe2LWmfAxoJ3AzqLuJ7SAFp8+F1n1wUCtQ@mail.gmail.com>
Date: Mon, 25 Nov 2024 14:44:25 +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, len.brown@...el.com, 
	artem.bityutskiy@...ux.intel.com, dave.hansen@...ux.intel.com, 
	peterz@...radead.org, tglx@...utronix.de, gautham.shenoy@....com
Subject: Re: [RFC PATCH v4 6/8] intel_idle: Provide enter_dead() handler for SRF

On Mon, Nov 25, 2024 at 2:21 PM Patryk Wlazlyn
<patryk.wlazlyn@...ux.intel.com> wrote:
>
> Intel's Sierra Forest report two C6 substates in cpuid leaf 5:
>     C6S  (hint 0x22)
>     C6SP (hint 0x23)
>
> Hints 0x20 and 0x21 are skipped entirely, causing the generic
> implementation in mwait_play_dead() to compute the wrong hint, when
> looking for the deepest cstate. As a result, package with an offlined
> CPU can never reach PC6.

Is this still the case with the latest firmware?

If so, this could be the second patch in the series if [1-3/7] are dropped.

Otherwise, I don't think it is needed any more.

> Define the enter_dead() handler for SRF.
>
> Signed-off-by: Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>
> ---
>  drivers/idle/intel_idle.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> index ac4d8faa3886..c2ca01e74add 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_with_hint(eax);
> +}
> +
>  /*
>   * States are indexed by the cstate number,
>   * which is also the index into the MWAIT hint array.
> @@ -1391,6 +1402,7 @@ static struct cpuidle_state srf_cstates[] __initdata = {
>                 .exit_latency = 1,
>                 .target_residency = 1,
>                 .enter = &intel_idle,
> +               .enter_dead = &intel_idle_enter_dead,
>                 .enter_s2idle = intel_idle_s2idle, },
>         {
>                 .name = "C1E",
> @@ -1399,6 +1411,7 @@ static struct cpuidle_state srf_cstates[] __initdata = {
>                 .exit_latency = 2,
>                 .target_residency = 10,
>                 .enter = &intel_idle,
> +               .enter_dead = &intel_idle_enter_dead,
>                 .enter_s2idle = intel_idle_s2idle, },
>         {
>                 .name = "C6S",
> @@ -1408,6 +1421,7 @@ static struct cpuidle_state srf_cstates[] __initdata = {
>                 .exit_latency = 270,
>                 .target_residency = 700,
>                 .enter = &intel_idle,
> +               .enter_dead = &intel_idle_enter_dead,
>                 .enter_s2idle = intel_idle_s2idle, },
>         {
>                 .name = "C6SP",
> @@ -1417,6 +1431,7 @@ static struct cpuidle_state srf_cstates[] __initdata = {
>                 .exit_latency = 310,
>                 .target_residency = 900,
>                 .enter = &intel_idle,
> +               .enter_dead = &intel_idle_enter_dead,
>                 .enter_s2idle = intel_idle_s2idle, },
>         {
>                 .enter = NULL }
> --
> 2.47.0
>
>