gpio: add LP3943 I2C GPIO expander driver

This is one of LP3943 MFD driver.
LP3943 is configurable as a GPIO expander, up to 16 GPIOs.

* Application note: how to configure LP3943 as a GPIO expander
  http://www.ti.com/lit/an/snva287a/snva287a.pdf

* Supported GPIO controller operations
  request, free, direction_input, direction_output, get and set

* GPIO direction register not supported
  LP3943 doesn't have the GPIO direction register. It only provides input and
  output status registers.
  So, private data for the direction should be handled manually.
  This variable is updated whenever the direction is changed and
  used in 'get' operation.

* Pin assignment
  A driver data, 'pin_used' is checked when a GPIO is requested.
  If the GPIO is already assigned, then returns as failure.
  If the GPIO is available, 'pin_used' is set.
  When the GPIO is not used anymore, then it is cleared.
  It is defined as unsigned long type for atomic bit operation APIs,
  but only LSB 16bits are used because LP3943 has 16 outputs.
Signed-off-by: Milo Kim <milo.kim@ti.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/gpio/Kconfig

@@ -381,6 +381,14 @@ config GPIO_ARIZONA
 	help
 	  Support for GPIOs on Wolfson Arizona class devices.
 
+config GPIO_LP3943
+	tristate "TI/National Semiconductor LP3943 GPIO expander"
+	depends on MFD_LP3943
+	help
+	  GPIO driver for LP3943 MFD.
+	  LP3943 can be used as a GPIO expander which provides up to 16 GPIOs.
+	  Open drain outputs are required for this usage.
+
 config GPIO_MAX7300
 	tristate "Maxim MAX7300 GPIO expander"
 	depends on I2C

drivers/gpio/Makefile

@@ -35,6 +35,7 @@ obj-$(CONFIG_GPIO_JANZ_TTL)	+= gpio-janz-ttl.o
 obj-$(CONFIG_GPIO_KEMPLD)	+= gpio-kempld.o
 obj-$(CONFIG_ARCH_KS8695)	+= gpio-ks8695.o
 obj-$(CONFIG_GPIO_INTEL_MID)	+= gpio-intel-mid.o
+obj-$(CONFIG_GPIO_LP3943)	+= gpio-lp3943.o
 obj-$(CONFIG_ARCH_LPC32XX)	+= gpio-lpc32xx.o
 obj-$(CONFIG_GPIO_LYNXPOINT)	+= gpio-lynxpoint.o
 obj-$(CONFIG_GPIO_MAX730X)	+= gpio-max730x.o

drivers/gpio/gpio-lp3943.c

+/*
+ * TI/National Semiconductor LP3943 GPIO driver
+ *
+ * Copyright 2013 Texas Instruments
+ *
+ * Author: Milo Kim <milo.kim@ti.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2.
+ */
+
+#include <linux/bitops.h>
+#include <linux/err.h>
+#include <linux/gpio.h>
+#include <linux/i2c.h>
+#include <linux/mfd/lp3943.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+enum lp3943_gpios {
+	LP3943_GPIO1,
+	LP3943_GPIO2,
+	LP3943_GPIO3,
+	LP3943_GPIO4,
+	LP3943_GPIO5,
+	LP3943_GPIO6,
+	LP3943_GPIO7,
+	LP3943_GPIO8,
+	LP3943_GPIO9,
+	LP3943_GPIO10,
+	LP3943_GPIO11,
+	LP3943_GPIO12,
+	LP3943_GPIO13,
+	LP3943_GPIO14,
+	LP3943_GPIO15,
+	LP3943_GPIO16,
+	LP3943_MAX_GPIO,
+};
+
+struct lp3943_gpio {
+	struct gpio_chip chip;
+	struct lp3943 *lp3943;
+	u16 input_mask;		/* 1 = GPIO is input direction, 0 = output */
+};
+
+static inline struct lp3943_gpio *to_lp3943_gpio(struct gpio_chip *_chip)
+{
+	return container_of(_chip, struct lp3943_gpio, chip);
+}
+
+static int lp3943_gpio_request(struct gpio_chip *chip, unsigned offset)
+{
+	struct lp3943_gpio *lp3943_gpio = to_lp3943_gpio(chip);
+	struct lp3943 *lp3943 = lp3943_gpio->lp3943;
+
+	/* Return an error if the pin is already assigned */
+	if (test_and_set_bit(offset, &lp3943->pin_used))
+		return -EBUSY;
+
+	return 0;
+}
+
+static void lp3943_gpio_free(struct gpio_chip *chip, unsigned offset)
+{
+	struct lp3943_gpio *lp3943_gpio = to_lp3943_gpio(chip);
+	struct lp3943 *lp3943 = lp3943_gpio->lp3943;
+
+	clear_bit(offset, &lp3943->pin_used);
+}
+
+static int lp3943_gpio_set_mode(struct lp3943_gpio *lp3943_gpio, u8 offset,
+				u8 val)
+{
+	struct lp3943 *lp3943 = lp3943_gpio->lp3943;
+	const struct lp3943_reg_cfg *mux = lp3943->mux_cfg;
+
+	return lp3943_update_bits(lp3943, mux[offset].reg, mux[offset].mask,
+				  val << mux[offset].shift);
+}
+
+static int lp3943_gpio_direction_input(struct gpio_chip *chip, unsigned offset)
+{
+	struct lp3943_gpio *lp3943_gpio = to_lp3943_gpio(chip);
+
+	lp3943_gpio->input_mask |= BIT(offset);
+
+	return lp3943_gpio_set_mode(lp3943_gpio, offset, LP3943_GPIO_IN);
+}
+
+static int lp3943_get_gpio_in_status(struct lp3943_gpio *lp3943_gpio,
+				     struct gpio_chip *chip, unsigned offset)
+{
+	u8 addr, read;
+	int err;
+
+	switch (offset) {
+	case LP3943_GPIO1 ... LP3943_GPIO8:
+		addr = LP3943_REG_GPIO_A;
+		break;
+	case LP3943_GPIO9 ... LP3943_GPIO16:
+		addr = LP3943_REG_GPIO_B;
+		offset = offset - 8;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	err = lp3943_read_byte(lp3943_gpio->lp3943, addr, &read);
+	if (err)
+		return err;
+
+	return !!(read & BIT(offset));
+}
+
+static int lp3943_get_gpio_out_status(struct lp3943_gpio *lp3943_gpio,
+				      struct gpio_chip *chip, unsigned offset)
+{
+	struct lp3943 *lp3943 = lp3943_gpio->lp3943;
+	const struct lp3943_reg_cfg *mux = lp3943->mux_cfg;
+	u8 read;
+	int err;
+
+	err = lp3943_read_byte(lp3943, mux[offset].reg, &read);
+	if (err)
+		return err;
+
+	read = (read & mux[offset].mask) >> mux[offset].shift;
+
+	if (read == LP3943_GPIO_OUT_HIGH)
+		return 1;
+	else if (read == LP3943_GPIO_OUT_LOW)
+		return 0;
+	else
+		return -EINVAL;
+}
+
+static int lp3943_gpio_get(struct gpio_chip *chip, unsigned offset)
+{
+	struct lp3943_gpio *lp3943_gpio = to_lp3943_gpio(chip);
+
+	/*
+	 * Limitation:
+	 *   LP3943 doesn't have the GPIO direction register. It provides
+	 *   only input and output status registers.
+	 *   So, direction info is required to handle the 'get' operation.
+	 *   This variable is updated whenever the direction is changed and
+	 *   it is used here.
+	 */
+
+	if (lp3943_gpio->input_mask & BIT(offset))
+		return lp3943_get_gpio_in_status(lp3943_gpio, chip, offset);
+	else
+		return lp3943_get_gpio_out_status(lp3943_gpio, chip, offset);
+}
+
+static void lp3943_gpio_set(struct gpio_chip *chip, unsigned offset, int value)
+{
+	struct lp3943_gpio *lp3943_gpio = to_lp3943_gpio(chip);
+	u8 data;
+
+	if (value)
+		data = LP3943_GPIO_OUT_HIGH;
+	else
+		data = LP3943_GPIO_OUT_LOW;
+
+	lp3943_gpio_set_mode(lp3943_gpio, offset, data);
+}
+
+static int lp3943_gpio_direction_output(struct gpio_chip *chip, unsigned offset,
+					int value)
+{
+	struct lp3943_gpio *lp3943_gpio = to_lp3943_gpio(chip);
+
+	lp3943_gpio_set(chip, offset, value);
+	lp3943_gpio->input_mask &= ~BIT(offset);
+
+	return 0;
+}
+
+static const struct gpio_chip lp3943_gpio_chip = {
+	.label			= "lp3943",
+	.owner			= THIS_MODULE,
+	.request		= lp3943_gpio_request,
+	.free			= lp3943_gpio_free,
+	.direction_input	= lp3943_gpio_direction_input,
+	.get			= lp3943_gpio_get,
+	.direction_output	= lp3943_gpio_direction_output,
+	.set			= lp3943_gpio_set,
+	.base			= -1,
+	.ngpio			= LP3943_MAX_GPIO,
+	.can_sleep		= 1,
+};
+
+static int lp3943_gpio_probe(struct platform_device *pdev)
+{
+	struct lp3943 *lp3943 = dev_get_drvdata(pdev->dev.parent);
+	struct lp3943_gpio *lp3943_gpio;
+
+	lp3943_gpio = devm_kzalloc(&pdev->dev, sizeof(*lp3943_gpio),
+				GFP_KERNEL);
+	if (!lp3943_gpio)
+		return -ENOMEM;
+
+	lp3943_gpio->lp3943 = lp3943;
+	lp3943_gpio->chip = lp3943_gpio_chip;
+	lp3943_gpio->chip.dev = &pdev->dev;
+
+	platform_set_drvdata(pdev, lp3943_gpio);
+
+	return gpiochip_add(&lp3943_gpio->chip);
+}
+
+static int lp3943_gpio_remove(struct platform_device *pdev)
+{
+	struct lp3943_gpio *lp3943_gpio = platform_get_drvdata(pdev);
+
+	return gpiochip_remove(&lp3943_gpio->chip);
+}
+
+static const struct of_device_id lp3943_gpio_of_match[] = {
+	{ .compatible = "ti,lp3943-gpio", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, lp3943_gpio_of_match);
+
+static struct platform_driver lp3943_gpio_driver = {
+	.probe = lp3943_gpio_probe,
+	.remove = lp3943_gpio_remove,
+	.driver = {
+		.name = "lp3943-gpio",
+		.owner = THIS_MODULE,
+		.of_match_table = of_match_ptr(lp3943_gpio_of_match),
+	},
+};
+module_platform_driver(lp3943_gpio_driver);
+
+MODULE_DESCRIPTION("LP3943 GPIO driver");
+MODULE_ALIAS("platform:lp3943-gpio");
+MODULE_AUTHOR("Milo Kim");
+MODULE_LICENSE("GPL");