pinctrl: sh-pfc: Implement pinconf power-source param for voltage switching

The pfc in the R8A7790 (and probably others in the R-Car gen 2 family)
supports switching SDHI signals between 3.3V and 1.8V nominal voltage,
and the SD driver should do that when switching to and from UHS modes.

Add a flag for pins that have configurable I/O voltage and SoC
operations to get and set the nominal voltage.  Implement the pinconf
power-source parameter using these operations.
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/renesas,pfc-pinctrl.txt

@@ -71,7 +71,9 @@ Pin Configuration Node Properties:
 
 The pin configuration parameters use the generic pinconf bindings defined in
 pinctrl-bindings.txt in this directory. The supported parameters are
-bias-disable, bias-pull-up and bias-pull-down.
+bias-disable, bias-pull-up, bias-pull-down and power-source. For pins that
+have a configurable I/O voltage, the power-source value should be the
+nominal I/O voltage in millivolts.
 
 
 GPIO

drivers/pinctrl/sh-pfc/pinctrl.c

@@ -491,6 +491,9 @@ static bool sh_pfc_pinconf_validate(struct sh_pfc *pfc, unsigned int _pin,
 	case PIN_CONFIG_BIAS_PULL_DOWN:
 		return pin->configs & SH_PFC_PIN_CFG_PULL_DOWN;
 
+	case PIN_CONFIG_POWER_SOURCE:
+		return pin->configs & SH_PFC_PIN_CFG_IO_VOLTAGE;
+
 	default:
 		return false;
 	}
@@ -503,7 +506,6 @@ static int sh_pfc_pinconf_get(struct pinctrl_dev *pctldev, unsigned _pin,
 	struct sh_pfc *pfc = pmx->pfc;
 	enum pin_config_param param = pinconf_to_config_param(*config);
 	unsigned long flags;
-	unsigned int bias;
 
 	if (!sh_pfc_pinconf_validate(pfc, _pin, param))
 		return -ENOTSUPP;
@@ -511,7 +513,9 @@ static int sh_pfc_pinconf_get(struct pinctrl_dev *pctldev, unsigned _pin,
 	switch (param) {
 	case PIN_CONFIG_BIAS_DISABLE:
 	case PIN_CONFIG_BIAS_PULL_UP:
-	case PIN_CONFIG_BIAS_PULL_DOWN:
+	case PIN_CONFIG_BIAS_PULL_DOWN: {
+		unsigned int bias;
+
 		if (!pfc->info->ops || !pfc->info->ops->get_bias)
 			return -ENOTSUPP;
 
@@ -524,6 +528,24 @@ static int sh_pfc_pinconf_get(struct pinctrl_dev *pctldev, unsigned _pin,
 
 		*config = 0;
 		break;
+	}
+
+	case PIN_CONFIG_POWER_SOURCE: {
+		int ret;
+
+		if (!pfc->info->ops || !pfc->info->ops->get_io_voltage)
+			return -ENOTSUPP;
+
+		spin_lock_irqsave(&pfc->lock, flags);
+		ret = pfc->info->ops->get_io_voltage(pfc, _pin);
+		spin_unlock_irqrestore(&pfc->lock, flags);
+
+		if (ret < 0)
+			return ret;
+
+		*config = ret;
+		break;
+	}
 
 	default:
 		return -ENOTSUPP;
@@ -560,6 +582,24 @@ static int sh_pfc_pinconf_set(struct pinctrl_dev *pctldev, unsigned _pin,
 
 			break;
 
+		case PIN_CONFIG_POWER_SOURCE: {
+			unsigned int arg =
+				pinconf_to_config_argument(configs[i]);
+			int ret;
+
+			if (!pfc->info->ops || !pfc->info->ops->set_io_voltage)
+				return -ENOTSUPP;
+
+			spin_lock_irqsave(&pfc->lock, flags);
+			ret = pfc->info->ops->set_io_voltage(pfc, _pin, arg);
+			spin_unlock_irqrestore(&pfc->lock, flags);
+
+			if (ret)
+				return ret;
+
+			break;
+		}
+
 		default:
 			return -ENOTSUPP;
 		}

drivers/pinctrl/sh-pfc/sh_pfc.h

@@ -12,6 +12,7 @@
 #define __SH_PFC_H
 
 #include <linux/bug.h>
+#include <linux/pinctrl/pinconf-generic.h>
 #include <linux/stringify.h>
 
 enum {
@@ -26,6 +27,7 @@ enum {
 #define SH_PFC_PIN_CFG_OUTPUT		(1 << 1)
 #define SH_PFC_PIN_CFG_PULL_UP		(1 << 2)
 #define SH_PFC_PIN_CFG_PULL_DOWN	(1 << 3)
+#define SH_PFC_PIN_CFG_IO_VOLTAGE	(1 << 4)
 #define SH_PFC_PIN_CFG_NO_GPIO		(1 << 31)
 
 struct sh_pfc_pin {
@@ -121,6 +123,9 @@ struct sh_pfc_soc_operations {
 	unsigned int (*get_bias)(struct sh_pfc *pfc, unsigned int pin);
 	void (*set_bias)(struct sh_pfc *pfc, unsigned int pin,
 			 unsigned int bias);
+	int (*get_io_voltage)(struct sh_pfc *pfc, unsigned int pin);
+	int (*set_io_voltage)(struct sh_pfc *pfc, unsigned int pin,
+			      u16 voltage_mV);
 };
 
 struct sh_pfc_soc_info {