linux-kernel - Re: [PATCH v2 2/4] pmdomain: Respect the CPU system-wakeup QoS limit during s2idle

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Message-ID: <CAJZ5v0hPUYoLFs=jZ10a1cX6TE1bmRF7CkBH1Ebejao9Hdfhnw@mail.gmail.com>
Date: Thu, 30 Oct 2025 11:44:56 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>, linux-pm@...r.kernel.org, 
	Vincent Guittot <vincent.guittot@...aro.org>, Peter Zijlstra <peterz@...radead.org>, 
	Kevin Hilman <khilman@...libre.com>, Pavel Machek <pavel@...nel.org>, Len Brown <len.brown@...el.com>, 
	Daniel Lezcano <daniel.lezcano@...aro.org>, Saravana Kannan <saravanak@...gle.com>, 
	Maulik Shah <quic_mkshah@...cinc.com>, Prasad Sodagudi <psodagud@...cinc.com>, 
	Dhruva Gole <d-gole@...com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] pmdomain: Respect the CPU system-wakeup QoS limit
 during s2idle

On Thu, Oct 16, 2025 at 5:19 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> A CPU system-wakeup QoS limit may have been requested by user-space. To
> avoid breaking this constraint when entering a low-power state during
> s2idle through genpd, let's extend the corresponding genpd governor for
> CPUs. More precisely, during s2idle let the genpd governor select a
> suitable low-power state, by taking into account the QoS limit.
>
> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> ---
>
> Changes in v2:
>         - Limite the change to the genpd governor for CPUs.
>
> ---
>  drivers/pmdomain/core.c     | 10 ++++++++--
>  drivers/pmdomain/governor.c | 27 +++++++++++++++++++++++++++
>  include/linux/pm_domain.h   |  1 +
>  3 files changed, 36 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
> index 61c2277c9ce3..4fd546ef0448 100644
> --- a/drivers/pmdomain/core.c
> +++ b/drivers/pmdomain/core.c
> @@ -1425,8 +1425,14 @@ static void genpd_sync_power_off(struct generic_pm_domain *genpd, bool use_lock,
>                         return;
>         }
>
> -       /* Choose the deepest state when suspending */
> -       genpd->state_idx = genpd->state_count - 1;
> +       if (genpd->gov && genpd->gov->system_power_down_ok) {
> +               if (!genpd->gov->system_power_down_ok(&genpd->domain))
> +                       return;
> +       } else {
> +               /* Default to the deepest state. */
> +               genpd->state_idx = genpd->state_count - 1;
> +       }
> +
>         if (_genpd_power_off(genpd, false)) {
>                 genpd->states[genpd->state_idx].rejected++;
>                 return;
> diff --git a/drivers/pmdomain/governor.c b/drivers/pmdomain/governor.c
> index 39359811a930..bd1b9d66d4a5 100644
> --- a/drivers/pmdomain/governor.c
> +++ b/drivers/pmdomain/governor.c
> @@ -415,9 +415,36 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
>         return false;
>  }
>
> +static bool cpu_system_power_down_ok(struct dev_pm_domain *pd)
> +{
> +       s64 constraint_ns = cpu_wakeup_latency_qos_limit() * NSEC_PER_USEC;

I'm not sure why genpd needs to take cpu_wakeup_latency_qos_limit()
into account directly.

It should be told by cpuidle which state has been selected on the CPU
side and it should not go any deeper than that anyway.

> +       struct generic_pm_domain *genpd = pd_to_genpd(pd);
> +       int state_idx = genpd->state_count - 1;
> +
> +       if (!(genpd->flags & GENPD_FLAG_CPU_DOMAIN)) {
> +               genpd->state_idx = state_idx;
> +               return true;
> +       }
> +
> +       /* Find the deepest state for the latency constraint. */
> +       while (state_idx >= 0) {
> +               s64 latency_ns = genpd->states[state_idx].power_off_latency_ns +
> +                                genpd->states[state_idx].power_on_latency_ns;
> +
> +               if (latency_ns <= constraint_ns) {
> +                       genpd->state_idx = state_idx;
> +                       return true;
> +               }
> +               state_idx--;
> +       }
> +
> +       return false;
> +}
> +
>  struct dev_power_governor pm_domain_cpu_gov = {
>         .suspend_ok = default_suspend_ok,
>         .power_down_ok = cpu_power_down_ok,
> +       .system_power_down_ok = cpu_system_power_down_ok,
>  };
>  #endif
>
> diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
> index f67a2cb7d781..93ba0143ca47 100644
> --- a/include/linux/pm_domain.h
> +++ b/include/linux/pm_domain.h
> @@ -153,6 +153,7 @@ enum genpd_sync_state {
>  };
>
>  struct dev_power_governor {
> +       bool (*system_power_down_ok)(struct dev_pm_domain *domain);
>         bool (*power_down_ok)(struct dev_pm_domain *domain);
>         bool (*suspend_ok)(struct device *dev);
>  };
> --
> 2.43.0
>