irqchip/imx-intmux: Implement intmux runtime power management

When the system is suspended, we can explicitly disable clock to save
power. To achieve this, we need save registers' state since it could be
lost after power off.

Implement power management which will:
- Turn the clock off after probing
- Disable clock and save registers' state on system suspend, as
  well as enable clock and restore registers' state on resume
- Rely on the Power Domain framework to shutdown the intmux
  power domain

Without CONFIG_PM, the clock is always on after probe stage.

Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
[maz: revamped commit message]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200727141734.24890-2-qiangqing.zhang@nxp.com

drivers/irqchip/irq-imx-intmux.c

@@ -53,13 +53,16 @@
 #include <linux/of_irq.h>
 #include <linux/of_platform.h>
 #include <linux/spinlock.h>
+#include <linux/pm_runtime.h>
 
 #define CHANIER(n)	(0x10 + (0x40 * n))
 #define CHANIPR(n)	(0x20 + (0x40 * n))
 
 #define CHAN_MAX_NUM		0x8
 
 struct intmux_irqchip_data {
+	struct irq_chip		chip;
+	u32			saved_reg;
 	int			chanidx;
 	int			irq;
 	struct irq_domain	*domain;
@@ -120,8 +123,10 @@ static struct irq_chip imx_intmux_irq_chip = {
 static int imx_intmux_irq_map(struct irq_domain *h, unsigned int irq,
 			      irq_hw_number_t hwirq)
 {
-	irq_set_chip_data(irq, h->host_data);
-	irq_set_chip_and_handler(irq, &imx_intmux_irq_chip, handle_level_irq);
+	struct intmux_irqchip_data *data = h->host_data;
+
+	irq_set_chip_data(irq, data);
+	irq_set_chip_and_handler(irq, &data->chip, handle_level_irq);
 
 	return 0;
 }
@@ -231,13 +236,19 @@ static int imx_intmux_probe(struct platform_device *pdev)
 	data->channum = channum;
 	raw_spin_lock_init(&data->lock);
 
+	pm_runtime_get_noresume(&pdev->dev);
+	pm_runtime_set_active(&pdev->dev);
+	pm_runtime_enable(&pdev->dev);
+
 	ret = clk_prepare_enable(data->ipg_clk);
 	if (ret) {
 		dev_err(&pdev->dev, "failed to enable ipg clk: %d\n", ret);
 		return ret;
 	}
 
 	for (i = 0; i < channum; i++) {
+		data->irqchip_data[i].chip = imx_intmux_irq_chip;
+		data->irqchip_data[i].chip.parent_device = &pdev->dev;
 		data->irqchip_data[i].chanidx = i;
 
 		data->irqchip_data[i].irq = irq_of_parse_and_map(np, i);
@@ -266,6 +277,12 @@ static int imx_intmux_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, data);
 
+	/*
+	 * Let pm_runtime_put() disable clock.
+	 * If CONFIG_PM is not enabled, the clock will stay powered.
+	 */
+	pm_runtime_put(&pdev->dev);
+
 	return 0;
 out:
 	clk_disable_unprepare(data->ipg_clk);
@@ -287,11 +304,56 @@ static int imx_intmux_remove(struct platform_device *pdev)
 		irq_domain_remove(data->irqchip_data[i].domain);
 	}
 
+	pm_runtime_disable(&pdev->dev);
+
+	return 0;
+}
+
+#ifdef CONFIG_PM
+static int imx_intmux_runtime_suspend(struct device *dev)
+{
+	struct intmux_data *data = dev_get_drvdata(dev);
+	struct intmux_irqchip_data irqchip_data;
+	int i;
+
+	for (i = 0; i < data->channum; i++) {
+		irqchip_data = data->irqchip_data[i];
+		irqchip_data.saved_reg = readl_relaxed(data->regs + CHANIER(i));
+	}
+
 	clk_disable_unprepare(data->ipg_clk);
 
 	return 0;
 }
 
+static int imx_intmux_runtime_resume(struct device *dev)
+{
+	struct intmux_data *data = dev_get_drvdata(dev);
+	struct intmux_irqchip_data irqchip_data;
+	int ret, i;
+
+	ret = clk_prepare_enable(data->ipg_clk);
+	if (ret) {
+		dev_err(dev, "failed to enable ipg clk: %d\n", ret);
+		return ret;
+	}
+
+	for (i = 0; i < data->channum; i++) {
+		irqchip_data = data->irqchip_data[i];
+		writel_relaxed(irqchip_data.saved_reg, data->regs + CHANIER(i));
+	}
+
+	return 0;
+}
+#endif
+
+static const struct dev_pm_ops imx_intmux_pm_ops = {
+	SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend,
+				      pm_runtime_force_resume)
+	SET_RUNTIME_PM_OPS(imx_intmux_runtime_suspend,
+			   imx_intmux_runtime_resume, NULL)
+};
+
 static const struct of_device_id imx_intmux_id[] = {
 	{ .compatible = "fsl,imx-intmux", },
 	{ /* sentinel */ },
@@ -301,6 +363,7 @@ static struct platform_driver imx_intmux_driver = {
 	.driver = {
 		.name = "imx-intmux",
 		.of_match_table = imx_intmux_id,
+		.pm = &imx_intmux_pm_ops,
 	},
 	.probe = imx_intmux_probe,
 	.remove = imx_intmux_remove,