pinctrl: at91-pio4: add support for drive strength

Add support for the drive strength configuration. Usually, this value is
expressed in mA. Since the numeric value depends on VDDIOP voltage, a
value we can't retrieve at runtime, the controller uses low, medium and
high to define the drive strength.

The PIO controller accepts two values for the low drive configuration: 0
and 1. Most of the time, we don't care about the drive strength. So we
keep the default value which is 0. The drive strength is advertised
through the sysfs only when it has been explicitly set in the device
tree i.e. if its value is different from 0.

Signed-off-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Author: ldesroches

Documentation/devicetree/bindings/pinctrl/atmel,at91-pio4-pinctrl.txt

@@ -36,6 +36,8 @@ Optional properties:
 - GENERIC_PINCONFIG: generic pinconfig options to use, bias-disable,
 bias-pull-down, bias-pull-up, drive-open-drain, input-schmitt-enable,
 input-debounce, output-low, output-high.
+- atmel,drive-strength: 0 or 1 for low drive, 2 for medium drive and 3 for
+high drive. The default value is low drive.
 
 Example:
 
@@ -66,6 +68,7 @@ Example:
 			pinmux = <PIN_PB0>,
 				 <PIN_PB5>;
 			bias-pull-up;
+			atmel,drive-strength = <ATMEL_PIO_DRVSTR_ME>;
 		};
 
 		pinctrl_sdmmc1_default: sdmmc1_default {

drivers/pinctrl/pinctrl-at91-pio4.c

@@ -14,6 +14,7 @@
  * GNU General Public License for more details.
  */
 
+#include <dt-bindings/pinctrl/at91.h>
 #include <linux/clk.h>
 #include <linux/gpio/driver.h>
 /* FIXME: needed for gpio_to_irq(), get rid of this */
@@ -49,6 +50,8 @@
 #define		ATMEL_PIO_IFSCEN_MASK		BIT(13)
 #define		ATMEL_PIO_OPD_MASK		BIT(14)
 #define		ATMEL_PIO_SCHMITT_MASK		BIT(15)
+#define		ATMEL_PIO_DRVSTR_MASK		GENMASK(17, 16)
+#define		ATMEL_PIO_DRVSTR_OFFSET		16
 #define		ATMEL_PIO_CFGR_EVTSEL_MASK	GENMASK(26, 24)
 #define		ATMEL_PIO_CFGR_EVTSEL_FALLING	(0 << 24)
 #define		ATMEL_PIO_CFGR_EVTSEL_RISING	(1 << 24)
@@ -75,6 +78,9 @@
 #define ATMEL_GET_PIN_FUNC(pinfunc)	((pinfunc >> 16) & 0xf)
 #define ATMEL_GET_PIN_IOSET(pinfunc)	((pinfunc >> 20) & 0xf)
 
+/* Custom pinconf parameters */
+#define ATMEL_PIN_CONFIG_DRIVE_STRENGTH	(PIN_CONFIG_END + 1)
+
 struct atmel_pioctrl_data {
 	unsigned nbanks;
 };
@@ -139,6 +145,10 @@ static const char * const atmel_functions[] = {
 	"GPIO", "A", "B", "C", "D", "E", "F", "G"
 };
 
+static const struct pinconf_generic_params atmel_custom_bindings[] = {
+	{"atmel,drive-strength", ATMEL_PIN_CONFIG_DRIVE_STRENGTH, 0},
+};
+
 /* --- GPIO --- */
 static unsigned int atmel_gpio_read(struct atmel_pioctrl *atmel_pioctrl,
 				    unsigned int bank, unsigned int reg)
@@ -690,6 +700,11 @@ static int atmel_conf_pin_config_group_get(struct pinctrl_dev *pctldev,
 			return -EINVAL;
 		arg = 1;
 		break;
+	case ATMEL_PIN_CONFIG_DRIVE_STRENGTH:
+		if (!(res & ATMEL_PIO_DRVSTR_MASK))
+			return -EINVAL;
+		arg = (res & ATMEL_PIO_DRVSTR_MASK) >> ATMEL_PIO_DRVSTR_OFFSET;
+		break;
 	default:
 		return -ENOTSUPP;
 	}
@@ -775,6 +790,18 @@ static int atmel_conf_pin_config_group_set(struct pinctrl_dev *pctldev,
 					ATMEL_PIO_SODR);
 			}
 			break;
+		case ATMEL_PIN_CONFIG_DRIVE_STRENGTH:
+			switch (arg) {
+			case ATMEL_PIO_DRVSTR_LO:
+			case ATMEL_PIO_DRVSTR_ME:
+			case ATMEL_PIO_DRVSTR_HI:
+				conf &= (~ATMEL_PIO_DRVSTR_MASK);
+				conf |= arg << ATMEL_PIO_DRVSTR_OFFSET;
+				break;
+			default:
+				dev_warn(pctldev->dev, "drive strength not updated (incorrect value)\n");
+			}
+			break;
 		default:
 			dev_warn(pctldev->dev,
 				 "unsupported configuration parameter: %u\n",
@@ -814,6 +841,19 @@ static void atmel_conf_pin_config_dbg_show(struct pinctrl_dev *pctldev,
 		seq_printf(s, "%s ", "open-drain");
 	if (conf & ATMEL_PIO_SCHMITT_MASK)
 		seq_printf(s, "%s ", "schmitt");
+	if (conf & ATMEL_PIO_DRVSTR_MASK) {
+		switch ((conf & ATMEL_PIO_DRVSTR_MASK) >> ATMEL_PIO_DRVSTR_OFFSET) {
+		case ATMEL_PIO_DRVSTR_ME:
+			seq_printf(s, "%s ", "medium-drive");
+			break;
+		case ATMEL_PIO_DRVSTR_HI:
+			seq_printf(s, "%s ", "high-drive");
+			break;
+		/* ATMEL_PIO_DRVSTR_LO and 0 which is the default value at reset */
+		default:
+			seq_printf(s, "%s ", "low-drive");
+		}
+	}
 }
 
 static const struct pinconf_ops atmel_confops = {
@@ -954,6 +994,8 @@ static int atmel_pinctrl_probe(struct platform_device *pdev)
 		return -ENOMEM;
 	atmel_pinctrl_desc.pins = pin_desc;
 	atmel_pinctrl_desc.npins = atmel_pioctrl->npins;
+	atmel_pinctrl_desc.num_custom_params = ARRAY_SIZE(atmel_custom_bindings);
+	atmel_pinctrl_desc.custom_params = atmel_custom_bindings;
 
 	/* One pin is one group since a pin can achieve all functions. */
 	group_names = devm_kzalloc(dev, sizeof(*group_names)

include/dt-bindings/pinctrl/at91.h

@@ -39,4 +39,8 @@
 #define AT91_PERIPH_C		3
 #define AT91_PERIPH_D		4
 
+#define ATMEL_PIO_DRVSTR_LO	1
+#define ATMEL_PIO_DRVSTR_ME	2
+#define ATMEL_PIO_DRVSTR_HI	3
+
 #endif /* __DT_BINDINGS_AT91_PINCTRL_H__ */