linux-kernel - Re: [PATCH v6 6/7] drm/panthor: Use existing OPP table if present

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Message-ID: <CAPaKu7Q==RvuZR-pgJekF++Y4HOdkryEvYV8QGJd_os0_if_vQ@mail.gmail.com>
Date: Fri, 3 Oct 2025 13:47:39 -0700
From: Chia-I Wu <olvaffe@...il.com>
To: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
	Boris Brezillon <boris.brezillon@...labora.com>, Jassi Brar <jassisinghbrar@...il.com>, 
	Chen-Yu Tsai <wenst@...omium.org>, Steven Price <steven.price@....com>, 
	Liviu Dudau <liviu.dudau@....com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Matthias Brugger <matthias.bgg@...il.com>, Kees Cook <kees@...nel.org>, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, Ulf Hansson <ulf.hansson@...aro.org>, kernel@...labora.com, 
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-mediatek@...ts.infradead.org, linux-hardening@...r.kernel.org, 
	linux-pm@...r.kernel.org
Subject: Re: [PATCH v6 6/7] drm/panthor: Use existing OPP table if present

On Fri, Oct 3, 2025 at 1:16 PM Nicolas Frattaroli
<nicolas.frattaroli@...labora.com> wrote:
>
> On SoCs where the GPU's power-domain is in charge of setting performance
> levels, the OPP table of the GPU node will have already been populated
> during said power-domain's attach_dev operation.
>
> To avoid initialising an OPP table twice, only set the OPP regulator and
> the OPPs from DT if there's no OPP table present.
>
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
> ---
>  drivers/gpu/drm/panthor/panthor_devfreq.c | 26 ++++++++++++++++----------
>  1 file changed, 16 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/panthor/panthor_devfreq.c b/drivers/gpu/drm/panthor/panthor_devfreq.c
> index 978f193a2aee561fadd9a976e9b1417118260889..6beb6170d6eea3dd65880dfe64a61abbdd5f08da 100644
> --- a/drivers/gpu/drm/panthor/panthor_devfreq.c
> +++ b/drivers/gpu/drm/panthor/panthor_devfreq.c
> @@ -143,6 +143,7 @@ int panthor_devfreq_init(struct panthor_device *ptdev)
>         struct panthor_devfreq *pdevfreq;
>         struct dev_pm_opp *opp;
>         unsigned long cur_freq;
> +       struct opp_table *t;
>         unsigned long freq = ULONG_MAX;
>         int ret;
>
> @@ -152,18 +153,23 @@ int panthor_devfreq_init(struct panthor_device *ptdev)
>
>         ptdev->devfreq = pdevfreq;
>
> -       ret = devm_pm_opp_set_regulators(dev, reg_names);
> -       if (ret) {
> -               if (ret != -EPROBE_DEFER)
> -                       DRM_DEV_ERROR(dev, "Couldn't set OPP regulators\n");
> -
> -               return ret;
> +       t = dev_pm_opp_get_opp_table(dev);
"t" is too short for a long function like this one. We should either
rename it to "opp_table" or refactor this out to a shorter function.

dev_pm_domain_set_performance_state is new to me. It might just be me,
but a short comment explaining that the opp table might have been set
up by the pmdomain can be helpful.

With that, Reviewed-by: Chia-I Wu <olvaffe@...il.com>.

> +       if (IS_ERR_OR_NULL(t)) {
> +               ret = devm_pm_opp_set_regulators(dev, reg_names);
> +               if (ret) {
> +                       if (ret != -EPROBE_DEFER)
> +                               DRM_DEV_ERROR(dev, "Couldn't set OPP regulators\n");
> +
> +                       return ret;
> +               }
> +
> +               ret = devm_pm_opp_of_add_table(dev);
> +               if (ret)
> +                       return ret;
> +       } else {
> +               dev_pm_opp_put_opp_table(t);
>         }
>
> -       ret = devm_pm_opp_of_add_table(dev);
> -       if (ret)
> -               return ret;
> -
>         spin_lock_init(&pdevfreq->lock);
>
>         panthor_devfreq_reset(pdevfreq);
>
> --
> 2.51.0
>