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From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Wed, 13 Mar 2024 20:49:38 +0100
Message-ID: <CAJZ5v0g_UcJzRy2-16kjOZpOyB=-FsdgH63LJBzmHRhsARYjVA@mail.gmail.com>
Subject: Re: [PATCH] PM: EM: Force device drivers to provide power in uW
To: Lukasz Luba <lukasz.luba@arm.com>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, rafael@kernel.org, 
	poshao.chen@mediatek.com
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On Fri, Mar 8, 2024 at 1:31=E2=80=AFPM Lukasz Luba <lukasz.luba@arm.com> wr=
ote:
>
> The EM only supports power in uW. Make sure that it is not possible to
> register some downstream driver which doesn't provide power in uW.
> The only exception is artificial EM, but that EM is ignored by the rest o=
f
> kernel frameworks (thermal, powercap, etc).
>
> Reported-by: PoShao Chen <poshao.chen@mediatek.com>
> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
> ---
>
> Hi all,
>
> The was an issue reported recently that the EM could be used with
> not aligned drivers which provide milli-Watts. This patch prevents such
> drivers to register EM (although there are no such in upstream).
>
> Regards,
> Lukasz
>
>  kernel/power/energy_model.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index b686ac0345bd9..9e1c9aa399ea9 100644
> --- a/kernel/power/energy_model.c
> +++ b/kernel/power/energy_model.c
> @@ -612,6 +612,17 @@ int em_dev_register_perf_domain(struct device *dev, =
unsigned int nr_states,
>         else if (cb->get_cost)
>                 flags |=3D EM_PERF_DOMAIN_ARTIFICIAL;
>
> +       /*
> +        * EM only supports uW (exception is artificial EM).
> +        * Therefore, check and force the drivers to provide
> +        * power in uW.
> +        */
> +       if (!microwatts && !(flags & EM_PERF_DOMAIN_ARTIFICIAL)) {
> +               dev_err(dev, "EM: only supports uW power values\n");
> +               ret =3D -EINVAL;
> +               goto unlock;
> +       }
> +
>         ret =3D em_create_pd(dev, nr_states, cb, cpus, flags);
>         if (ret)
>                 goto unlock;
> --

Applied as 6.9-rc material, thanks!