drm/panfrost: Implement ability to turn on/off regulators in suspend

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>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231109102543.42971-6-angelogioacchino.delregno@collabora.com

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_set_opp(dev, opp);
+		dev_pm_opp_put(opp);
+	}
+
 	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->clock);
 	}
 
+	if (pfdev->comp->pm_features & BIT(GPU_PM_VREG_OFF))
+		dev_pm_opp_set_opp(dev, NULL);
+
 	return 0;
 }
 

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 {