rtc: stm32: add pinctrl and pinmux interfaces

STM32 RTC is capable to handle 3 specific pins of the soc.
"out1, out2 and out2_rmp". To handle this, we use pinctrl framework.
There is a single pin per group.
Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240722160022.454226-3-valentin.caron@foss.st.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/Kconfig

@@ -1923,6 +1923,11 @@ config RTC_DRV_STM32
 	tristate "STM32 RTC"
 	select REGMAP_MMIO
 	depends on ARCH_STM32 || COMPILE_TEST
+	depends on OF
+	depends on PINCTRL
+	select PINMUX
+	select PINCONF
+	select GENERIC_PINCONF
 	help
 	   If you say yes here you get support for the STM32 On-Chip
 	   Real Time Clock.

drivers/rtc/rtc-stm32.c

@@ -13,6 +13,9 @@
 #include <linux/mfd/syscon.h>
 #include <linux/module.h>
 #include <linux/of.h>
+#include <linux/pinctrl/pinctrl.h>
+#include <linux/pinctrl/pinconf-generic.h>
+#include <linux/pinctrl/pinmux.h>
 #include <linux/platform_device.h>
 #include <linux/pm_wakeirq.h>
 #include <linux/regmap.h>
@@ -107,6 +110,14 @@
 /* STM32 RTC driver time helpers */
 #define SEC_PER_DAY		(24 * 60 * 60)
 
+/* STM32 RTC pinctrl helpers */
+#define STM32_RTC_PINMUX(_name, _action, ...) { \
+	.name = (_name), \
+	.action = (_action), \
+	.groups = ((const char *[]){ __VA_ARGS__ }), \
+	.num_groups = ARRAY_SIZE(((const char *[]){ __VA_ARGS__ })), \
+}
+
 struct stm32_rtc;
 
 struct stm32_rtc_registers {
@@ -171,6 +182,106 @@ static void stm32_rtc_wpr_lock(struct stm32_rtc *rtc)
 	writel_relaxed(RTC_WPR_WRONG_KEY, rtc->base + regs->wpr);
 }
 
+enum stm32_rtc_pin_name {
+	NONE,
+	OUT1,
+	OUT2,
+	OUT2_RMP
+};
+
+static const struct pinctrl_pin_desc stm32_rtc_pinctrl_pins[] = {
+	PINCTRL_PIN(OUT1, "out1"),
+	PINCTRL_PIN(OUT2, "out2"),
+	PINCTRL_PIN(OUT2_RMP, "out2_rmp"),
+};
+
+static int stm32_rtc_pinctrl_get_groups_count(struct pinctrl_dev *pctldev)
+{
+	return ARRAY_SIZE(stm32_rtc_pinctrl_pins);
+}
+
+static const char *stm32_rtc_pinctrl_get_group_name(struct pinctrl_dev *pctldev,
+						    unsigned int selector)
+{
+	return stm32_rtc_pinctrl_pins[selector].name;
+}
+
+static int stm32_rtc_pinctrl_get_group_pins(struct pinctrl_dev *pctldev,
+					    unsigned int selector,
+					    const unsigned int **pins,
+					    unsigned int *num_pins)
+{
+	*pins = &stm32_rtc_pinctrl_pins[selector].number;
+	*num_pins = 1;
+	return 0;
+}
+
+static const struct pinctrl_ops stm32_rtc_pinctrl_ops = {
+	.dt_node_to_map		= pinconf_generic_dt_node_to_map_all,
+	.dt_free_map		= pinconf_generic_dt_free_map,
+	.get_groups_count	= stm32_rtc_pinctrl_get_groups_count,
+	.get_group_name		= stm32_rtc_pinctrl_get_group_name,
+	.get_group_pins		= stm32_rtc_pinctrl_get_group_pins,
+};
+
+struct stm32_rtc_pinmux_func {
+	const char *name;
+	const char * const *groups;
+	const unsigned int num_groups;
+	int (*action)(struct pinctrl_dev *pctl_dev, unsigned int pin);
+};
+
+static const struct stm32_rtc_pinmux_func stm32_rtc_pinmux_functions[] = {
+};
+
+static int stm32_rtc_pinmux_get_functions_count(struct pinctrl_dev *pctldev)
+{
+	return ARRAY_SIZE(stm32_rtc_pinmux_functions);
+}
+
+static const char *stm32_rtc_pinmux_get_fname(struct pinctrl_dev *pctldev, unsigned int selector)
+{
+	return stm32_rtc_pinmux_functions[selector].name;
+}
+
+static int stm32_rtc_pinmux_get_groups(struct pinctrl_dev *pctldev, unsigned int selector,
+				       const char * const **groups, unsigned int * const num_groups)
+{
+	*groups = stm32_rtc_pinmux_functions[selector].groups;
+	*num_groups = stm32_rtc_pinmux_functions[selector].num_groups;
+	return 0;
+}
+
+static int stm32_rtc_pinmux_set_mux(struct pinctrl_dev *pctldev, unsigned int selector,
+				    unsigned int group)
+{
+	struct stm32_rtc_pinmux_func selected_func = stm32_rtc_pinmux_functions[selector];
+	struct pinctrl_pin_desc pin = stm32_rtc_pinctrl_pins[group];
+
+	/* Call action */
+	if (selected_func.action)
+		return selected_func.action(pctldev, pin.number);
+
+	return -EINVAL;
+}
+
+static const struct pinmux_ops stm32_rtc_pinmux_ops = {
+	.get_functions_count	= stm32_rtc_pinmux_get_functions_count,
+	.get_function_name	= stm32_rtc_pinmux_get_fname,
+	.get_function_groups	= stm32_rtc_pinmux_get_groups,
+	.set_mux		= stm32_rtc_pinmux_set_mux,
+	.strict			= true,
+};
+
+static struct pinctrl_desc stm32_rtc_pdesc = {
+	.name = DRIVER_NAME,
+	.pins = stm32_rtc_pinctrl_pins,
+	.npins = ARRAY_SIZE(stm32_rtc_pinctrl_pins),
+	.owner = THIS_MODULE,
+	.pctlops = &stm32_rtc_pinctrl_ops,
+	.pmxops = &stm32_rtc_pinmux_ops,
+};
+
 static int stm32_rtc_enter_init_mode(struct stm32_rtc *rtc)
 {
 	const struct stm32_rtc_registers *regs = &rtc->data->regs;
@@ -791,6 +902,7 @@ static int stm32_rtc_probe(struct platform_device *pdev)
 {
 	struct stm32_rtc *rtc;
 	const struct stm32_rtc_registers *regs;
+	struct pinctrl_dev *pctl;
 	int ret;
 
 	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
@@ -912,6 +1024,14 @@ static int stm32_rtc_probe(struct platform_device *pdev)
 		goto err;
 	}
 
+	ret = devm_pinctrl_register_and_init(&pdev->dev, &stm32_rtc_pdesc, rtc, &pctl);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret, "pinctrl register failed");
+
+	ret = pinctrl_enable(pctl);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret, "pinctrl enable failed");
+
 	/*
 	 * If INITS flag is reset (calendar year field set to 0x00), calendar
 	 * must be initialized