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

[Karunika Choo <karunika.choo@arm.com>]

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@gmail.com>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.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) {

Is there a reason to not fail on -ENODEV? I would assume it is a valid 
failure path. 

Kind regards,
Karunika Choo

> +			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);
>