[DRIVER] fxl6408: add I2C GPIO expander driver

Add minimal driver for Fairchild FXL6408 8-bit I2C-controlled GPIO expander.
Missing feature: IRQ handling.

Imported from: https://git.toradex.com/cgit/linux-toradex.git/?h=toradex_5.4-2.3.x-imx

drivers/gpio/Kconfig

@@ -281,6 +281,13 @@ config GPIO_FTGPIO010
 	  Support for common GPIOs from the Faraday FTGPIO010 IP core, found in
 	  Cortina systems Gemini platforms, Moxa ART and others.
 
+config GPIO_FXL6408
+	tristate "FXL6408 I2C GPIO expander"
+	help
+	  GPIO driver for Fairchild Semiconductor FXL6408 GPIO expander.
+	  To compile this driver as a module, choose M here: the module
+	  will be called gpio-fxl6408.
+
 config GPIO_GENERIC_PLATFORM
 	tristate "Generic memory-mapped GPIO controller support (MMIO platform device)"
 	select GPIO_GENERIC

drivers/gpio/Makefile

@@ -59,6 +59,7 @@ obj-$(CONFIG_GPIO_EP93XX)		+= gpio-ep93xx.o
 obj-$(CONFIG_GPIO_EXAR)			+= gpio-exar.o
 obj-$(CONFIG_GPIO_F7188X)		+= gpio-f7188x.o
 obj-$(CONFIG_GPIO_FTGPIO010)		+= gpio-ftgpio010.o
+obj-$(CONFIG_GPIO_FXL6408)		+= gpio-fxl6408.o
 obj-$(CONFIG_GPIO_GE_FPGA)		+= gpio-ge.o
 obj-$(CONFIG_GPIO_GPIO_MM)		+= gpio-gpio-mm.o
 obj-$(CONFIG_GPIO_GRGPIO)		+= gpio-grgpio.o

drivers/gpio/gpio-fxl6408.c

+/*
+ *  Copyright (C) 2016 Broadcom Limited.
+ *
+ *  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 of the License.
+ */
+
+/**
+ * DOC: FXL6408 I2C to GPIO expander.
+ *
+ * This chip has has 8 GPIO lines out of it, and is controlled by an
+ * I2C bus (a pair of lines), providing 4x expansion of GPIO lines.
+ * It also provides an interrupt line out for notifying of
+ * statechanges.
+ *
+ * Any preconfigured state will be left in place until the GPIO lines
+ * get activated.  At power on, everything is treated as an input.
+ *
+ * Documentation can be found at:
+ * https://www.fairchildsemi.com/datasheets/FX/FXL6408.pdf
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/gpio.h>
+#include <linux/i2c.h>
+#include <linux/slab.h>
+#include <linux/of_platform.h>
+
+#define FXL6408_DEVICE_ID		0x01
+# define FXL6408_RST_INT		BIT(1)
+# define FXL6408_SW_RST			BIT(0)
+
+/* Bits set here indicate that the GPIO is an output. */
+#define FXL6408_IO_DIR			0x03
+/* Bits set here, when the corresponding bit of IO_DIR is set, drive
+ * the output high instead of low.
+ */
+#define FXL6408_OUTPUT			0x05
+/* Bits here make the output High-Z, instead of the OUTPUT value. */
+#define FXL6408_OUTPUT_HIGH_Z		0x07
+/* Bits here define the expected input state of the GPIO.
+ * INTERRUPT_STAT bits will be set when the INPUT transitions away
+ * from this value.
+ */
+#define FXL6408_INPUT_DEFAULT_STATE	0x09
+/* Bits here enable either pull up or pull down according to
+ * FXL6408_PULL_DOWN.
+ */
+#define FXL6408_PULL_ENABLE		0x0b
+/* Bits set here (when the corresponding PULL_ENABLE is set) enable a
+ * pull-up instead of a pull-down.
+ */
+#define FXL6408_PULL_UP			0x0d
+/* Returns the current status (1 = HIGH) of the input pins. */
+#define FXL6408_INPUT_STATUS		0x0f
+/* Mask of pins which can generate interrupts. */
+#define FXL6408_INTERRUPT_MASK		0x11
+/* Mask of pins which have generated an interrupt.  Cleared on read. */
+#define FXL6408_INTERRUPT_STAT		0x13
+
+struct fxl6408_chip {
+	struct gpio_chip gpio_chip;
+	struct i2c_client *client;
+	struct mutex i2c_lock;
+
+	/* Caches of register values so we don't have to read-modify-write. */
+	u8 reg_io_dir;
+	u8 reg_output;
+};
+
+static int fxl6408_gpio_direction_input(struct gpio_chip *gc, unsigned off)
+{
+	struct fxl6408_chip *chip = gpiochip_get_data(gc);
+
+	mutex_lock(&chip->i2c_lock);
+	chip->reg_io_dir &= ~BIT(off);
+	i2c_smbus_write_byte_data(chip->client, FXL6408_IO_DIR,
+				  chip->reg_io_dir);
+	mutex_unlock(&chip->i2c_lock);
+
+	return 0;
+}
+
+static int fxl6408_gpio_direction_output(struct gpio_chip *gc,
+		unsigned off, int val)
+{
+	struct fxl6408_chip *chip = gpiochip_get_data(gc);
+
+	mutex_lock(&chip->i2c_lock);
+	chip->reg_io_dir |= BIT(off);
+	i2c_smbus_write_byte_data(chip->client, FXL6408_IO_DIR,
+				  chip->reg_io_dir);
+	mutex_unlock(&chip->i2c_lock);
+
+	return 0;
+}
+
+static int fxl6408_gpio_get_direction(struct gpio_chip *gc, unsigned off)
+{
+	struct fxl6408_chip *chip = gpiochip_get_data(gc);
+
+	return (chip->reg_io_dir & BIT(off)) == 0;
+}
+
+static int fxl6408_gpio_get_value(struct gpio_chip *gc, unsigned off)
+{
+	struct fxl6408_chip *chip = gpiochip_get_data(gc);
+	u8 reg;
+
+	if (fxl6408_gpio_get_direction(gc, off) == 0)
+	{
+		reg = chip->reg_output;
+	} else {
+		mutex_lock(&chip->i2c_lock);
+		reg = i2c_smbus_read_byte_data(chip->client, FXL6408_INPUT_STATUS);
+		mutex_unlock(&chip->i2c_lock);
+	}
+	return (reg & BIT(off)) != 0;
+}
+
+static void fxl6408_gpio_set_value(struct gpio_chip *gc, unsigned off, int val)
+{
+	struct fxl6408_chip *chip = gpiochip_get_data(gc);
+
+	mutex_lock(&chip->i2c_lock);
+
+	if (val)
+		chip->reg_output |= BIT(off);
+	else
+		chip->reg_output &= ~BIT(off);
+
+	i2c_smbus_write_byte_data(chip->client, FXL6408_OUTPUT,
+				  chip->reg_output);
+	mutex_unlock(&chip->i2c_lock);
+}
+
+
+static void fxl6408_gpio_set_multiple(struct gpio_chip *gc,
+		unsigned long *mask, unsigned long *bits)
+{
+	struct fxl6408_chip *chip = gpiochip_get_data(gc);
+	mutex_lock(&chip->i2c_lock);
+	chip->reg_output = (chip->reg_output & ~mask[0]) | bits[0];
+	i2c_smbus_write_byte_data(chip->client, FXL6408_OUTPUT,
+				  chip->reg_output);
+	mutex_unlock(&chip->i2c_lock);
+}
+
+static int fxl6408_probe(struct i2c_client *client,
+			 const struct i2c_device_id *id)
+{
+	struct device *dev = &client->dev;
+	struct fxl6408_chip *chip;
+	struct gpio_chip *gc;
+	unsigned int val;
+	int ret;
+	u8 device_id;
+
+	/* Check the device ID register to see if it's responding.
+	 * This also clears RST_INT as a side effect, so we won't get
+	 * the "we've been power cycled" interrupt once we enable
+	 * interrupts.
+	 */
+	device_id = i2c_smbus_read_byte_data(client, FXL6408_DEVICE_ID);
+	if (device_id < 0) {
+		dev_err(dev, "FXL6408 probe returned %d\n", device_id);
+		return device_id;
+	} else if (device_id >> 5 != 5) {
+		dev_err(dev, "FXL6408 probe returned DID: 0x%02x\n", device_id);
+		return -ENODEV;
+	}
+
+	/* Disable High-Z of outputs, so that our OUTPUT updates
+	 * actually take effect.
+	 */
+	i2c_smbus_write_byte_data(client, FXL6408_OUTPUT_HIGH_Z, 0);
+
+	chip = devm_kzalloc(dev, sizeof(struct fxl6408_chip), GFP_KERNEL);
+	if (chip == NULL)
+		return -ENOMEM;
+
+	chip->client = client;
+	mutex_init(&chip->i2c_lock);
+
+	/* if configured, set initial output state and direction,
+	 * otherwise read them from the chip */
+	if (of_property_read_u32(dev->of_node, "inital_io_dir", &val)) {
+		chip->reg_io_dir = i2c_smbus_read_byte_data(client, FXL6408_IO_DIR);
+	} else {
+		chip->reg_io_dir = val & 0xff;
+		i2c_smbus_write_byte_data(client, FXL6408_IO_DIR, chip->reg_io_dir);
+	}
+	if (of_property_read_u32(dev->of_node, "inital_output", &val)) {
+		chip->reg_output = i2c_smbus_read_byte_data(client, FXL6408_OUTPUT);
+	} else {
+		chip->reg_output = val & 0xff;
+		i2c_smbus_write_byte_data(client, FXL6408_OUTPUT, chip->reg_output);
+	}
+
+	gc = &chip->gpio_chip;
+	gc->direction_input  = fxl6408_gpio_direction_input;
+	gc->direction_output = fxl6408_gpio_direction_output;
+	gc->get_direction = fxl6408_gpio_get_direction;
+	gc->get = fxl6408_gpio_get_value;
+	gc->set = fxl6408_gpio_set_value;
+	gc->set_multiple = fxl6408_gpio_set_multiple;
+	gc->can_sleep = true;
+
+	gc->base =-1;
+	gc->ngpio = 8;
+	gc->label = chip->client->name;
+	gc->parent = dev;
+	gc->owner = THIS_MODULE;
+
+	ret = gpiochip_add_data(gc, chip);
+	if (ret)
+		return ret;
+
+	i2c_set_clientdata(client, chip);
+	return 0;
+}
+
+static int fxl6408_remove(struct i2c_client *client)
+{
+	struct fxl6408_chip *chip = i2c_get_clientdata(client);
+
+	gpiochip_remove(&chip->gpio_chip);
+
+	return 0;
+}
+
+static const struct of_device_id fxl6408_dt_ids[] = {
+	{ .compatible = "fcs,fxl6408" },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(of, fxl6408_dt_ids);
+
+static const struct i2c_device_id fxl6408_id[] = {
+	{ "fxl6408", 0 },
+	{ },
+};
+MODULE_DEVICE_TABLE(i2c, fxl6408_id);
+
+static struct i2c_driver fxl6408_driver = {
+	.driver = {
+		.name	= "fxl6408",
+		.of_match_table = fxl6408_dt_ids,
+	},
+	.probe		= fxl6408_probe,
+	.remove		= fxl6408_remove,
+	.id_table	= fxl6408_id,
+};
+
+module_i2c_driver(fxl6408_driver);
+
+MODULE_AUTHOR("Eric Anholt <eric@anholt.net>");
+MODULE_DESCRIPTION("GPIO expander driver for FXL6408");
+MODULE_LICENSE("GPL");