linux-kernel - Re: [PATCH v5 1/2] PM / Domains: Add support for 'required-opps' to set default perf state

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Date:   Mon, 2 Aug 2021 14:59:20 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Rajendra Nayak <rnayak@...eaurora.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Roja Rani Yarubandi <rojay@...eaurora.org>,
        Stephan Gerhold <stephan@...hold.net>
Subject: Re: [PATCH v5 1/2] PM / Domains: Add support for 'required-opps' to
 set default perf state

On Tue, 20 Jul 2021 at 09:12, Rajendra Nayak <rnayak@...eaurora.org> wrote:
>
> Some devices within power domains with performance states do not
> support DVFS, but still need to vote on a default/static state
> while they are active. They can express this using the 'required-opps'
> property in device tree, which points to the phandle of the OPP
> supported by the corresponding power-domains.
>
> Add support to parse this information from DT and then set the
> specified performance state during attach and drop it on detach.
> runtime suspend/resume callbacks already have logic to drop/set
> the vote as needed and should take care of dropping the default
> perf state vote on runtime suspend and restore it back on runtime
> resume.
>
> Signed-off-by: Rajendra Nayak <rnayak@...eaurora.org>
> ---
>  drivers/base/power/domain.c | 28 +++++++++++++++++++++++++---
>  include/linux/pm_domain.h   |  1 +
>  2 files changed, 26 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index a934c67..f454031 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -2598,6 +2598,12 @@ static void genpd_dev_pm_detach(struct device *dev, bool power_off)
>
>         dev_dbg(dev, "removing from PM domain %s\n", pd->name);
>
> +       /* Drop the default performance state */
> +       if (dev_gpd_data(dev)->default_pstate) {
> +               dev_pm_genpd_set_performance_state(dev, 0);
> +               dev_gpd_data(dev)->default_pstate = 0;
> +       }
> +
>         for (i = 1; i < GENPD_RETRY_MAX_MS; i <<= 1) {
>                 ret = genpd_remove_device(pd, dev);
>                 if (ret != -EAGAIN)
> @@ -2635,9 +2641,10 @@ static void genpd_dev_pm_sync(struct device *dev)
>  static int __genpd_dev_pm_attach(struct device *dev, struct device *base_dev,
>                                  unsigned int index, bool power_on)
>  {
> +       struct device_node *np;
>         struct of_phandle_args pd_args;
>         struct generic_pm_domain *pd;
> -       int ret;
> +       int ret, pstate;
>
>         ret = of_parse_phandle_with_args(dev->of_node, "power-domains",
>                                 "#power-domain-cells", index, &pd_args);
> @@ -2675,10 +2682,25 @@ static int __genpd_dev_pm_attach(struct device *dev, struct device *base_dev,
>                 genpd_unlock(pd);
>         }
>
> -       if (ret)
> +       if (ret) {
>                 genpd_remove_device(pd, dev);
> +               return -EPROBE_DEFER;
> +       }
> +
> +       /* Set the default performance state */
> +       np = base_dev->of_node;

Please use dev->of_node instead (it is set to the same of_node as
base_dev by the callers of __genpd_dev_pm_attach) as it's more
consistent with existing code.

> +       if (of_parse_phandle(np, "required-opps", index)) {
> +               pstate = of_get_required_opp_performance_state(np, index);
> +               if (pstate < 0) {
> +                       ret = pstate;
> +                       dev_err(dev, "failed to set required performance state for power-domain %s: %d\n",
> +                               pd->name, ret);
> +               }
> +               dev_pm_genpd_set_performance_state(dev, pstate);
> +               dev_gpd_data(dev)->default_pstate = pstate;

This doesn't look entirely correct to me. If we fail to translate a
required opp to a performance state, we shouldn't try to set it.

Perhaps it's also easier to call
of_get_required_opp_performance_state() unconditionally of whether a
"required-opps" specifier exists. If it fails with the translation,
then we just skip setting a default state and continue with returning
1.

Would that work?

> +       }
>
> -       return ret ? -EPROBE_DEFER : 1;
> +       return ret ? ret : 1;
>  }
>
>  /**
> diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
> index 21a0577..67017c9 100644
> --- a/include/linux/pm_domain.h
> +++ b/include/linux/pm_domain.h
> @@ -198,6 +198,7 @@ struct generic_pm_domain_data {
>         struct notifier_block *power_nb;
>         int cpu;
>         unsigned int performance_state;
> +       unsigned int default_pstate;
>         unsigned int rpm_pstate;
>         ktime_t next_wakeup;
>         void *data;
> --
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
> of Code Aurora Forum, hosted by The Linux Foundation
>

Kind regards
Uffe