pwm: stm32: Add power management support

Add suspend/resume PM sleep ops. When going to low power, enforce the PWM
channel isn't active. Let the PWM consumers disable it during their own
suspend sequence, see [1]. So, perform a check here, and handle the
pinctrl states. Also restore the break inputs upon resume, as registers
content may be lost when going to low power mode.

[1] https://lkml.org/lkml/2019/2/5/770

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-stm32.c

@@ -12,6 +12,7 @@
 #include <linux/mfd/stm32-timers.h>
 #include <linux/module.h>
 #include <linux/of.h>
+#include <linux/pinctrl/consumer.h>
 #include <linux/platform_device.h>
 #include <linux/pwm.h>
 
@@ -659,6 +660,42 @@ static int stm32_pwm_remove(struct platform_device *pdev)
 	return 0;
 }
 
+static int __maybe_unused stm32_pwm_suspend(struct device *dev)
+{
+	struct stm32_pwm *priv = dev_get_drvdata(dev);
+	unsigned int i;
+	u32 ccer, mask;
+
+	/* Look for active channels */
+	ccer = active_channels(priv);
+
+	for (i = 0; i < priv->chip.npwm; i++) {
+		mask = TIM_CCER_CC1E << (i * 4);
+		if (ccer & mask) {
+			dev_err(dev, "PWM %u still in use by consumer %s\n",
+				i, priv->chip.pwms[i].label);
+			return -EBUSY;
+		}
+	}
+
+	return pinctrl_pm_select_sleep_state(dev);
+}
+
+static int __maybe_unused stm32_pwm_resume(struct device *dev)
+{
+	struct stm32_pwm *priv = dev_get_drvdata(dev);
+	int ret;
+
+	ret = pinctrl_pm_select_default_state(dev);
+	if (ret)
+		return ret;
+
+	/* restore breakinput registers that may have been lost in low power */
+	return stm32_pwm_apply_breakinputs(priv);
+}
+
+static SIMPLE_DEV_PM_OPS(stm32_pwm_pm_ops, stm32_pwm_suspend, stm32_pwm_resume);
+
 static const struct of_device_id stm32_pwm_of_match[] = {
 	{ .compatible = "st,stm32-pwm",	},
 	{ /* end node */ },
@@ -671,6 +708,7 @@ static struct platform_driver stm32_pwm_driver = {
 	.driver	= {
 		.name = "stm32-pwm",
 		.of_match_table = stm32_pwm_of_match,
+		.pm = &stm32_pwm_pm_ops,
 	},
 };
 module_platform_driver(stm32_pwm_driver);