Re: [PATCH 3/4] drm/panfrost: Implement ability to turn on/off regulators in suspend

[Steven Price <steven.price@arm.com>]

On 30/10/2023 13:22, AngeloGioacchino Del Regno wrote:
> Some platforms/SoCs can power off the GPU entirely by completely cutting
> off power, greatly enhancing battery time during system suspend: add a
> new pm_feature GPU_PM_VREG_OFF to allow turning off the GPU regulators
> during full suspend only on selected platforms.
> 
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> ---
>  drivers/gpu/drm/panfrost/panfrost_device.c | 19 ++++++++++++++++++-
>  drivers/gpu/drm/panfrost/panfrost_device.h |  2 ++
>  2 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
> index 2022ed76a620..51b22eb0971d 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
> @@ -431,10 +431,21 @@ static int panfrost_device_resume(struct device *dev)
>  	struct panfrost_device *pfdev = dev_get_drvdata(dev);
>  	int ret;
>  
> +	if (pfdev->comp->pm_features & BIT(GPU_PM_VREG_OFF)) {
> +		unsigned long freq = pfdev->pfdevfreq.fast_rate;
> +		struct dev_pm_opp *opp;
> +
> +		opp = dev_pm_opp_find_freq_ceil(dev, &freq);
> +		if (IS_ERR(opp))
> +			return PTR_ERR(opp);
> +		dev_pm_opp_put(opp);
> +		dev_pm_opp_set_opp(dev, opp);

These lines look the wrong way round - surely we want to hang onto the
reference until the set_opp call is made?

Steve

> +	}
> +
>  	if (pfdev->comp->pm_features & BIT(GPU_PM_CLK_DIS)) {
>  		ret = clk_enable(pfdev->clock);
>  		if (ret)
> -			return ret;
> +			goto err_clk;
>  
>  		if (pfdev->bus_clock) {
>  			ret = clk_enable(pfdev->bus_clock);
> @@ -455,6 +466,9 @@ static int panfrost_device_resume(struct device *dev)
>  err_bus_clk:
>  	if (pfdev->comp->pm_features & BIT(GPU_PM_CLK_DIS))
>  		clk_disable(pfdev->clock);
> +err_clk:
> +	if (pfdev->comp->pm_features & BIT(GPU_PM_VREG_OFF))
> +		dev_pm_opp_set_opp(dev, NULL);
>  	return ret;
>  }
>  
> @@ -474,6 +488,9 @@ static int panfrost_device_suspend(struct device *dev)
>  			clk_disable(pfdev->bus_clock);
>  	}
>  
> +	if (pfdev->comp->pm_features & BIT(GPU_PM_VREG_OFF))
> +		dev_pm_opp_set_opp(dev, NULL);
> +
>  	return 0;
>  }
>  
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> index d7f179eb8ea3..0fc558db6bfd 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> @@ -28,9 +28,11 @@ struct panfrost_perfcnt;
>  /**
>   * enum panfrost_gpu_pm - Supported kernel power management features
>   * @GPU_PM_CLK_DIS:  Allow disabling clocks during system suspend
> + * @GPU_PM_VREG_OFF: Allow turning off regulators during system suspend
>   */
>  enum panfrost_gpu_pm {
>  	GPU_PM_CLK_DIS,
> +	GPU_PM_VREG_OFF,
>  };
>  
>  struct panfrost_features {