linux-kernel - Re: [PATCH v3 1/5] PM: domains: Allow a genpd consumer to require a synced power off

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Message-ID: <CAPDyKFr6Hf5gbJ9T9scYqDrg9tmKmVAm=h1J7r3GZzcogk5HpQ@mail.gmail.com>
Date:   Wed, 21 Dec 2022 15:43:01 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Akhil P Oommen <quic_akhilpo@...cinc.com>
Cc:     freedreno <freedreno@...ts.freedesktop.org>,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        Rob Clark <robdclark@...il.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kevin Hilman <khilman@...nel.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 1/5] PM: domains: Allow a genpd consumer to require a
 synced power off

On Tue, 20 Dec 2022 at 08:44, Akhil P Oommen <quic_akhilpo@...cinc.com> wrote:
>
> From: Ulf Hansson <ulf.hansson@...aro.org>
>
> Some genpd providers doesn't ensure that it has turned off at hardware.
> This is fine until the consumer really requires during some special
> scenarios that the power domain collapse at hardware before it is
> turned ON again.
>
> An example is the reset sequence of Adreno GPU which requires that the
> 'gpucc cx gdsc' power domain should move to OFF state in hardware at
> least once before turning in ON again to clear the internal state.
>
> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> Signed-off-by: Akhil P Oommen <quic_akhilpo@...cinc.com>
> ---
>
> (no changes since v2)
>
> Changes in v2:
> - Minor formatting fix
>
>  drivers/base/power/domain.c | 23 +++++++++++++++++++++++
>  include/linux/pm_domain.h   |  5 +++++
>  2 files changed, 28 insertions(+)
>
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index 967bcf9d415e..53524a102321 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -519,6 +519,28 @@ ktime_t dev_pm_genpd_get_next_hrtimer(struct device *dev)
>  }
>  EXPORT_SYMBOL_GPL(dev_pm_genpd_get_next_hrtimer);
>
> +/*
> + * dev_pm_genpd_synced_poweroff - Next power off should be synchronous
> + *
> + * @dev: A device that is attached to the genpd.
> + *
> + * Allows a consumer of the genpd to notify the provider that the next power off
> + * should be synchronous.

Nitpick; similar to other dev_pm_genpd_* function-descriptions, I
think it's important to add the below information.

"It is assumed that the users guarantee that the genpd wouldn't be
detached while this routine is getting called."

Can you please add that?

> + */
> +void dev_pm_genpd_synced_poweroff(struct device *dev)
> +{
> +       struct generic_pm_domain *genpd;
> +
> +       genpd = dev_to_genpd_safe(dev);
> +       if (!genpd)
> +               return;
> +
> +       genpd_lock(genpd);
> +       genpd->synced_poweroff = true;
> +       genpd_unlock(genpd);
> +}
> +EXPORT_SYMBOL_GPL(dev_pm_genpd_synced_poweroff);
> +
>  static int _genpd_power_on(struct generic_pm_domain *genpd, bool timed)
>  {
>         unsigned int state_idx = genpd->state_idx;
> @@ -562,6 +584,7 @@ static int _genpd_power_on(struct generic_pm_domain *genpd, bool timed)
>
>  out:
>         raw_notifier_call_chain(&genpd->power_notifiers, GENPD_NOTIFY_ON, NULL);
> +       genpd->synced_poweroff = false;
>         return 0;
>  err:
>         raw_notifier_call_chain(&genpd->power_notifiers, GENPD_NOTIFY_OFF,
> diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
> index 1cd41bdf73cf..f776fb93eaa0 100644
> --- a/include/linux/pm_domain.h
> +++ b/include/linux/pm_domain.h
> @@ -136,6 +136,7 @@ struct generic_pm_domain {
>         unsigned int prepared_count;    /* Suspend counter of prepared devices */
>         unsigned int performance_state; /* Aggregated max performance state */
>         cpumask_var_t cpus;             /* A cpumask of the attached CPUs */
> +       bool synced_poweroff;           /* A consumer needs a synced poweroff */
>         int (*power_off)(struct generic_pm_domain *domain);
>         int (*power_on)(struct generic_pm_domain *domain);
>         struct raw_notifier_head power_notifiers; /* Power on/off notifiers */
> @@ -235,6 +236,7 @@ int dev_pm_genpd_add_notifier(struct device *dev, struct notifier_block *nb);
>  int dev_pm_genpd_remove_notifier(struct device *dev);
>  void dev_pm_genpd_set_next_wakeup(struct device *dev, ktime_t next);
>  ktime_t dev_pm_genpd_get_next_hrtimer(struct device *dev);
> +void dev_pm_genpd_synced_poweroff(struct device *dev);
>
>  extern struct dev_power_governor simple_qos_governor;
>  extern struct dev_power_governor pm_domain_always_on_gov;
> @@ -300,6 +302,9 @@ static inline ktime_t dev_pm_genpd_get_next_hrtimer(struct device *dev)
>  {
>         return KTIME_MAX;
>  }
> +static inline void dev_pm_genpd_synced_poweroff(struct device *dev)
> +{ }
> +
>  #define simple_qos_governor            (*(struct dev_power_governor *)(NULL))
>  #define pm_domain_always_on_gov                (*(struct dev_power_governor *)(NULL))
>  #endif
> --
> 2.7.4
>

Kind regards
Uffe