counter: stm32-timer-cnt: add power management support

Add suspend/resume PM sleep ops. When going to low power, enforce the
counter isn't active. Gracefully restore its state upon resume in case
it's been left enabled prior to suspend.
Acked-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/counter/stm32-timer-cnt.c

@@ -12,6 +12,7 @@
 #include <linux/iio/types.h>
 #include <linux/mfd/stm32-timers.h>
 #include <linux/module.h>
+#include <linux/pinctrl/consumer.h>
 #include <linux/platform_device.h>
 
 #define TIM_CCMR_CCXS	(BIT(8) | BIT(0))
@@ -20,11 +21,20 @@
 #define TIM_CCER_MASK	(TIM_CCER_CC1P | TIM_CCER_CC1NP | \
 			 TIM_CCER_CC2P | TIM_CCER_CC2NP)
 
+struct stm32_timer_regs {
+	u32 cr1;
+	u32 cnt;
+	u32 smcr;
+	u32 arr;
+};
+
 struct stm32_timer_cnt {
 	struct counter_device counter;
 	struct regmap *regmap;
 	struct clk *clk;
 	u32 ceiling;
+	bool enabled;
+	struct stm32_timer_regs bak;
 };
 
 /**
@@ -224,6 +234,9 @@ static ssize_t stm32_count_enable_write(struct counter_device *counter,
 			clk_disable(priv->clk);
 	}
 
+	/* Keep enabled state to properly handle low power states */
+	priv->enabled = enable;
+
 	return len;
 }
 
@@ -358,10 +371,59 @@ static int stm32_timer_cnt_probe(struct platform_device *pdev)
 	priv->counter.num_signals = ARRAY_SIZE(stm32_signals);
 	priv->counter.priv = priv;
 
+	platform_set_drvdata(pdev, priv);
+
 	/* Register Counter device */
 	return devm_counter_register(dev, &priv->counter);
 }
 
+static int __maybe_unused stm32_timer_cnt_suspend(struct device *dev)
+{
+	struct stm32_timer_cnt *priv = dev_get_drvdata(dev);
+
+	/* Only take care of enabled counter: don't disturb other MFD child */
+	if (priv->enabled) {
+		/* Backup registers that may get lost in low power mode */
+		regmap_read(priv->regmap, TIM_SMCR, &priv->bak.smcr);
+		regmap_read(priv->regmap, TIM_ARR, &priv->bak.arr);
+		regmap_read(priv->regmap, TIM_CNT, &priv->bak.cnt);
+		regmap_read(priv->regmap, TIM_CR1, &priv->bak.cr1);
+
+		/* Disable the counter */
+		regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_CEN, 0);
+		clk_disable(priv->clk);
+	}
+
+	return pinctrl_pm_select_sleep_state(dev);
+}
+
+static int __maybe_unused stm32_timer_cnt_resume(struct device *dev)
+{
+	struct stm32_timer_cnt *priv = dev_get_drvdata(dev);
+	int ret;
+
+	ret = pinctrl_pm_select_default_state(dev);
+	if (ret)
+		return ret;
+
+	if (priv->enabled) {
+		clk_enable(priv->clk);
+
+		/* Restore registers that may have been lost */
+		regmap_write(priv->regmap, TIM_SMCR, priv->bak.smcr);
+		regmap_write(priv->regmap, TIM_ARR, priv->bak.arr);
+		regmap_write(priv->regmap, TIM_CNT, priv->bak.cnt);
+
+		/* Also re-enables the counter */
+		regmap_write(priv->regmap, TIM_CR1, priv->bak.cr1);
+	}
+
+	return 0;
+}
+
+static SIMPLE_DEV_PM_OPS(stm32_timer_cnt_pm_ops, stm32_timer_cnt_suspend,
+			 stm32_timer_cnt_resume);
+
 static const struct of_device_id stm32_timer_cnt_of_match[] = {
 	{ .compatible = "st,stm32-timer-counter", },
 	{},
@@ -373,6 +435,7 @@ static struct platform_driver stm32_timer_cnt_driver = {
 	.driver = {
 		.name = "stm32-timer-counter",
 		.of_match_table = stm32_timer_cnt_of_match,
+		.pm = &stm32_timer_cnt_pm_ops,
 	},
 };
 module_platform_driver(stm32_timer_cnt_driver);