linux-kernel - Re: [PATCH V3 3/3] OPP: Don't set OPP recursively for a parent genpd

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Date:   Wed, 22 Nov 2023 15:26:34 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Stephan Gerhold <stephan.gerhold@...nkonzept.com>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 3/3] OPP: Don't set OPP recursively for a parent genpd

On Thu, 16 Nov 2023 at 11:43, Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> Like other frameworks (clk, regulator, etc.) genpd core too takes care
> of propagation to performance state to parent genpds. The OPP core
> shouldn't attempt the same, or it may result in undefined behavior.
>
> Add checks at various places to take care of the same.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>

I think this looks good to me, even if I think it's a bit tricky to
consider the various scenarios. :-) Feel free to add:

Reviewed-by: Ulf Hansson <ulf.hansson@...aro.org>

Kind regards
Uffe

> ---
>  drivers/opp/core.c | 16 +++++++++++++++-
>  drivers/opp/of.c   |  7 +++++--
>  2 files changed, 20 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
> index e08375ed50aa..4f1ca84d9ed0 100644
> --- a/drivers/opp/core.c
> +++ b/drivers/opp/core.c
> @@ -2392,6 +2392,12 @@ static int _opp_attach_genpd(struct opp_table *opp_table, struct device *dev,
>                 return -EINVAL;
>         }
>
> +       /* Genpd core takes care of propagation to parent genpd */
> +       if (opp_table->is_genpd) {
> +               dev_err(dev, "%s: Operation not supported for genpds\n", __func__);
> +               return -EOPNOTSUPP;
> +       }
> +
>         /* Checking only the first one is enough ? */
>         if (opp_table->required_devs[0])
>                 return 0;
> @@ -2453,8 +2459,16 @@ static int _opp_set_required_devs(struct opp_table *opp_table,
>         if (opp_table->required_devs[0])
>                 return 0;
>
> -       for (i = 0; i < opp_table->required_opp_count; i++)
> +       for (i = 0; i < opp_table->required_opp_count; i++) {
> +               /* Genpd core takes care of propagation to parent genpd */
> +               if (required_devs[i] && opp_table->is_genpd &&
> +                   opp_table->required_opp_tables[i]->is_genpd) {
> +                       dev_err(dev, "%s: Operation not supported for genpds\n", __func__);
> +                       return -EOPNOTSUPP;
> +               }
> +
>                 opp_table->required_devs[i] = required_devs[i];
> +       }
>
>         return 0;
>  }
> diff --git a/drivers/opp/of.c b/drivers/opp/of.c
> index 5a7e294e56b7..f9f0b22bccbb 100644
> --- a/drivers/opp/of.c
> +++ b/drivers/opp/of.c
> @@ -339,8 +339,11 @@ static int _link_required_opps(struct dev_pm_opp *opp, struct opp_table *opp_tab
>          */
>         if (required_table->is_genpd && opp_table->required_opp_count == 1 &&
>             !opp_table->required_devs[0]) {
> -               if (!WARN_ON(opp->level != OPP_LEVEL_UNSET))
> -                       opp->level = opp->required_opps[0]->level;
> +               /* Genpd core takes care of propagation to parent genpd */
> +               if (!opp_table->is_genpd) {
> +                       if (!WARN_ON(opp->level != OPP_LEVEL_UNSET))
> +                               opp->level = opp->required_opps[0]->level;
> +               }
>         }
>
>         return 0;
> --
> 2.31.1.272.g89b43f80a514
>