linux-kernel - Re: [PATCH 08/10] PM: domains: Store the closest hrtimer event of the domain CPUs

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Date:   Tue, 25 Jan 2022 19:49:00 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Maulik Shah <quic_mkshah@...cinc.com>
Cc:     bjorn.andersson@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        rafael@...nel.org, daniel.lezcano@...aro.org,
        quic_lsrao@...cinc.com, quic_rjendra@...cinc.com
Subject: Re: [PATCH 08/10] PM: domains: Store the closest hrtimer event of the
 domain CPUs

On Sun, 9 Jan 2022 at 18:26, Maulik Shah <quic_mkshah@...cinc.com> wrote:
>
> The arch timer can not wake up the Qualcomm Technologies, Inc. (QTI)
> SoCs when the deepest CPUidle modes results in the SoC also to enter
> the low power mode.
>
> RSC is part of CPU subsystem and APSS rsc device is attached to cluster
> power domain. RSC has to setup next hrtimer wakeup in CONTROL_TCS which
> can wakeup the SoC from deepest low power states. The CONTROL_TCS does
> this by writing next wakeup in always on domain timer when the SoC is
> entering the low power state.
>
> Store the domain wakeup time from all the CPUs which can be used from
> domain power off callback by RSC device.
>
> Signed-off-by: Maulik Shah <quic_mkshah@...cinc.com>
> ---
>  drivers/base/power/domain_governor.c | 1 +
>  include/linux/pm_domain.h            | 1 +
>  2 files changed, 2 insertions(+)
>
> diff --git a/drivers/base/power/domain_governor.c b/drivers/base/power/domain_governor.c
> index cd08c58..a4c7dd8 100644
> --- a/drivers/base/power/domain_governor.c
> +++ b/drivers/base/power/domain_governor.c
> @@ -363,6 +363,7 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
>                                 domain_wakeup = next_hrtimer;
>                 }
>         }
> +       genpd->next_hrtimer = domain_wakeup;
>
>         /* The minimum idle duration is from now - until the next wakeup. */
>         idle_duration_ns = ktime_to_ns(ktime_sub(domain_wakeup, now));
> diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
> index 67017c9..682b372 100644
> --- a/include/linux/pm_domain.h
> +++ b/include/linux/pm_domain.h
> @@ -136,6 +136,7 @@ struct generic_pm_domain {
>         struct gpd_dev_ops dev_ops;
>         s64 max_off_time_ns;    /* Maximum allowed "suspended" time. */
>         ktime_t next_wakeup;    /* Maintained by the domain governor */
> +       ktime_t next_hrtimer;   /* Closest hrtimer event of the domain CPUs */

Would you mind clarifying the comment into something along the lines
of: "/* Next hrtimer for the CPU PM domain */

>         bool max_off_time_changed;
>         bool cached_power_down_ok;
>         bool cached_power_down_state_idx;
> --
> 2.7.4
>

Beside the nitpick above, I have a few additional minor comments.

*) Users of genpd->next_hrtimer should not access this member in the
struct generic_pm_domain themselves. Instead, I suggest we add a genpd
helper function to deal with this. In this regard, we should also add
a description to the helper function to explain under what *specific*
conditions it's allowed to be called for.

**) We should assign genpd->next_hrtimer a default value in
pm_genpd_init(). Perhaps that can also be used in a way to make sure
the helper function always returns a valid value!?

Other than this, I think the approach looks sane to me!

Kind regards
Uffe