linux-kernel - Re: [PATCH v8 4/5] drm/panthor: Use existing OPP table if present

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Message-ID: <ef6434a9-cde5-4d68-a3a3-1873ba7912d3@arm.com>
Date: Mon, 20 Oct 2025 14:47:30 +0100
From: Steven Price <steven.price@....com>
To: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 Boris Brezillon <boris.brezillon@...labora.com>,
 Jassi Brar <jassisinghbrar@...il.com>, Chia-I Wu <olvaffe@...il.com>,
 Chen-Yu Tsai <wenst@...omium.org>, 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>
Cc: 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 v8 4/5] drm/panthor: Use existing OPP table if present

On 17/10/2025 16:31, Nicolas Frattaroli 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.
> 
> Reviewed-by: Chia-I Wu <olvaffe@...il.com>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>

Reviewed-by: Steven Price <steven.price@....com>

> ---
>  drivers/gpu/drm/panthor/panthor_devfreq.c | 32 ++++++++++++++++++++++---------
>  1 file changed, 23 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_devfreq.c b/drivers/gpu/drm/panthor/panthor_devfreq.c
> index a6dca599f0a5..ec63e27f4883 100644
> --- a/drivers/gpu/drm/panthor/panthor_devfreq.c
> +++ b/drivers/gpu/drm/panthor/panthor_devfreq.c
> @@ -141,6 +141,7 @@ int panthor_devfreq_init(struct panthor_device *ptdev)
>  	struct thermal_cooling_device *cooling;
>  	struct device *dev = ptdev->base.dev;
>  	struct panthor_devfreq *pdevfreq;
> +	struct opp_table *table;
>  	struct dev_pm_opp *opp;
>  	unsigned long cur_freq;
>  	unsigned long freq = ULONG_MAX;
> @@ -152,17 +153,30 @@ int panthor_devfreq_init(struct panthor_device *ptdev)
>  
>  	ptdev->devfreq = pdevfreq;
>  
> -	ret = devm_pm_opp_set_regulators(dev, reg_names);
> -	if (ret && ret != -ENODEV) {
> -		if (ret != -EPROBE_DEFER)
> -			DRM_DEV_ERROR(dev, "Couldn't set OPP regulators\n");
> -		return ret;
> +	/*
> +	 * The power domain associated with the GPU may have already added an
> +	 * OPP table, complete with OPPs, as part of the platform bus
> +	 * initialization. If this is the case, the power domain is in charge of
> +	 * also controlling the performance, with a set_performance callback.
> +	 * Only add a new OPP table from DT if there isn't such a table present
> +	 * already.
> +	 */
> +	table = dev_pm_opp_get_opp_table(dev);
> +	if (IS_ERR_OR_NULL(table)) {
> +		ret = devm_pm_opp_set_regulators(dev, reg_names);
> +		if (ret && ret != -ENODEV) {
> +			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(table);
>  	}
>  
> -	ret = devm_pm_opp_of_add_table(dev);
> -	if (ret)
> -		return ret;
> -
>  	spin_lock_init(&pdevfreq->lock);
>  
>  	panthor_devfreq_reset(pdevfreq);
>