[PATCH v6 1/2] gpio: add GPO driver for PCA9570

[Sungbo Eo <mans0n@xxxxxxxxxx>]

NXP PCA9570 is a 4-bit I2C GPO expander without interrupt functionality.
Its ports are controlled only by a data byte without register address.

Datasheet: https://www.nxp.com/docs/en/data-sheet/PCA9570.pdf
Signed-off-by: Sungbo Eo <mans0n@xxxxxxxxxx>
---
v6:
* removed client
* re-added mutex
* removed template_chip

v5:
* amended the commit message
* removed unnecessary castings
* added data to of_match_table

v4:
* removed ->direction_input() and ->direction_output()
  (Seems unnecessary to me)
* removed ->set_multiple()
  (I'm not sure this implementation is really correct)
* added ->get()
  (DS says we can read the status from the device)
* read current status during probe

v3:
* remove mutex
* rename buffer to out
* simplify return statements
* replace ->probe() to ->probe_new()
* move ngpio to driver_data
  (PCA9571 is 8-bit so I thought making ngpio configurable is a good idea)

v2:
* move the direction functions below the set functions
* use devm_gpiochip_add_data() and remove the remove callback

v1:
Tested in kernel 5.4 on an ipq40xx platform.

This is my first time submitting a whole driver patch, and I'm not really
familiar with this PCA expander series.
Please let me know how I can improve this patch further.

FYI there's an unmerged patch for this chip.
http://driverdev.linuxdriverproject.org/pipermail/driverdev-devel/2017-May/105602.html
I don't have PCA9571 either so I didn't add support for it.
---
 drivers/gpio/Kconfig        |   8 ++
 drivers/gpio/Makefile       |   1 +
 drivers/gpio/gpio-pca9570.c | 146 ++++++++++++++++++++++++++++++++++++
 3 files changed, 155 insertions(+)
 create mode 100644 drivers/gpio/gpio-pca9570.c

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index c6b5c65c8405..d10dcb81b841 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -962,6 +962,14 @@ config GPIO_PCA953X_IRQ
 	  Say yes here to enable the pca953x to be used as an interrupt
 	  controller. It requires the driver to be built in the kernel.
 
+config GPIO_PCA9570
+	tristate "PCA9570 4-Bit I2C GPO expander"
+	help
+	  Say yes here to enable the GPO driver for the NXP PCA9570 chip.
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called gpio-pca9570.
+
 config GPIO_PCF857X
 	tristate "PCF857x, PCA{85,96}7x, and MAX732[89] I2C GPIO expanders"
 	select GPIOLIB_IRQCHIP
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index 1e4894e0bf0f..33cb40c28a61 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -110,6 +110,7 @@ obj-$(CONFIG_GPIO_OCTEON)		+= gpio-octeon.o
 obj-$(CONFIG_GPIO_OMAP)			+= gpio-omap.o
 obj-$(CONFIG_GPIO_PALMAS)		+= gpio-palmas.o
 obj-$(CONFIG_GPIO_PCA953X)		+= gpio-pca953x.o
+obj-$(CONFIG_GPIO_PCA9570)		+= gpio-pca9570.o
 obj-$(CONFIG_GPIO_PCF857X)		+= gpio-pcf857x.o
 obj-$(CONFIG_GPIO_PCH)			+= gpio-pch.o
 obj-$(CONFIG_GPIO_PCIE_IDIO_24)		+= gpio-pcie-idio-24.o
diff --git a/drivers/gpio/gpio-pca9570.c b/drivers/gpio/gpio-pca9570.c
new file mode 100644
index 000000000000..cb2b2f735c15
--- /dev/null
+++ b/drivers/gpio/gpio-pca9570.c
@@ -0,0 +1,146 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Driver for PCA9570 I2C GPO expander
+ *
+ * Copyright (C) 2020 Sungbo Eo <mans0n@xxxxxxxxxx>
+ *
+ * Based on gpio-tpic2810.c
+ * Copyright (C) 2015 Texas Instruments Incorporated - http://www.ti.com/
+ *	Andrew F. Davis <afd@xxxxxx>
+ */
+
+#include <linux/gpio/driver.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/property.h>
+
+/**
+ * struct pca9570 - GPIO driver data
+ * @chip: GPIO controller chip
+ * @lock: Protects write sequences
+ * @out: Buffer for device register
+ */
+struct pca9570 {
+	struct gpio_chip chip;
+	struct mutex lock;
+	u8 out;
+};
+
+static int pca9570_read(struct pca9570 *gpio, u8 *value)
+{
+	struct i2c_client *client = to_i2c_client(gpio->chip.parent);
+	int ret;
+
+	ret = i2c_smbus_read_byte(client);
+	if (ret < 0)
+		return ret;
+
+	*value = ret;
+	return 0;
+}
+
+static int pca9570_write(struct pca9570 *gpio, u8 value)
+{
+	struct i2c_client *client = to_i2c_client(gpio->chip.parent);
+
+	return i2c_smbus_write_byte(client, value);
+}
+
+static int pca9570_get_direction(struct gpio_chip *chip,
+				 unsigned offset)
+{
+	/* This device always output */
+	return GPIO_LINE_DIRECTION_OUT;
+}
+
+static int pca9570_get(struct gpio_chip *chip, unsigned offset)
+{
+	struct pca9570 *gpio = gpiochip_get_data(chip);
+	u8 buffer;
+	int ret;
+
+	ret = pca9570_read(gpio, &buffer);
+	if (ret)
+		return ret;
+
+	return !!(buffer & BIT(offset));
+}
+
+static void pca9570_set(struct gpio_chip *chip, unsigned offset, int value)
+{
+	struct pca9570 *gpio = gpiochip_get_data(chip);
+	u8 buffer;
+	int ret;
+
+	mutex_lock(&gpio->lock);
+
+	buffer = gpio->out;
+	if (value)
+		buffer |= BIT(offset);
+	else
+		buffer &= ~BIT(offset);
+
+	ret = pca9570_write(gpio, buffer);
+	if (ret)
+		goto out;
+
+	gpio->out = buffer;
+
+out:
+	mutex_unlock(&gpio->lock);
+}
+
+static int pca9570_probe(struct i2c_client *client)
+{
+	struct pca9570 *gpio;
+
+	gpio = devm_kzalloc(&client->dev, sizeof(*gpio), GFP_KERNEL);
+	if (!gpio)
+		return -ENOMEM;
+
+	gpio->chip.label = client->name;
+	gpio->chip.parent = &client->dev;
+	gpio->chip.owner = THIS_MODULE;
+	gpio->chip.get_direction = pca9570_get_direction;
+	gpio->chip.get = pca9570_get;
+	gpio->chip.set = pca9570_set;
+	gpio->chip.base = -1;
+	gpio->chip.ngpio = (uintptr_t)device_get_match_data(&client->dev);
+	gpio->chip.can_sleep = true;
+
+	mutex_init(&gpio->lock);
+
+	/* Read the current output level */
+	pca9570_read(gpio, &gpio->out);
+
+	i2c_set_clientdata(client, gpio);
+
+	return devm_gpiochip_add_data(&client->dev, &gpio->chip, gpio);
+}
+
+static const struct i2c_device_id pca9570_id_table[] = {
+	{ "pca9570", 4 },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(i2c, pca9570_id_table);
+
+static const struct of_device_id pca9570_of_match_table[] = {
+	{ .compatible = "nxp,pca9570", .data = (void *)4 },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, pca9570_of_match_table);
+
+static struct i2c_driver pca9570_driver = {
+	.driver = {
+		.name = "pca9570",
+		.of_match_table = pca9570_of_match_table,
+	},
+	.probe_new = pca9570_probe,
+	.id_table = pca9570_id_table,
+};
+module_i2c_driver(pca9570_driver);
+
+MODULE_AUTHOR("Sungbo Eo <mans0n@xxxxxxxxxx>");
+MODULE_DESCRIPTION("GPIO expander driver for PCA9570");
+MODULE_LICENSE("GPL v2");
-- 
2.27.0