gpio: Add a Gateworks PLD GPIO driver

This adds a driver for Gateworks PLD GPIO, that exist in
two instances on the Gateworks Cambria GW2358-4 router
platform at least.

Cc: Imre Kaloz <kaloz@openwrt.org>
Cc: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/Kconfig

@@ -831,6 +831,13 @@ config GPIO_ADNP
 	  enough to represent all pins, but the driver will assume a
 	  register layout for 64 pins (8 registers).
 
+config GPIO_GW_PLD
+	tristate "Gateworks PLD GPIO Expander"
+	depends on OF_GPIO
+	help
+	  Say yes here to provide access to the Gateworks I2C PLD GPIO
+	  Expander. This is used at least on the Cambria GW2358-4.
+
 config GPIO_MAX7300
 	tristate "Maxim MAX7300 GPIO expander"
 	select GPIO_MAX730X

drivers/gpio/Makefile

@@ -55,6 +55,7 @@ obj-$(CONFIG_GPIO_FTGPIO010)	+= gpio-ftgpio010.o
 obj-$(CONFIG_GPIO_GE_FPGA)	+= gpio-ge.o
 obj-$(CONFIG_GPIO_GPIO_MM)	+= gpio-gpio-mm.o
 obj-$(CONFIG_GPIO_GRGPIO)	+= gpio-grgpio.o
+obj-$(CONFIG_GPIO_GW_PLD)	+= gpio-gw-pld.o
 obj-$(CONFIG_GPIO_HLWD)		+= gpio-hlwd.o
 obj-$(CONFIG_HTC_EGPIO)		+= gpio-htc-egpio.o
 obj-$(CONFIG_GPIO_ICH)		+= gpio-ich.o

drivers/gpio/gpio-gw-pld.c

@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: GPL-2.0+
+//
+// Gateworks I2C PLD GPIO expander
+//
+// Copyright (C) 2019 Linus Walleij <linus.walleij@linaro.org>
+//
+// Based on code and know-how from the OpenWrt driver:
+// Copyright (C) 2009 Gateworks Corporation
+// Authors: Chris Lang, Imre Kaloz
+
+#include <linux/bits.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/gpio/driver.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+
+/**
+ * struct gw_pld - State container for Gateworks PLD
+ * @chip: GPIO chip instance
+ * @client: I2C client
+ * @out: shadow register for the output bute
+ */
+struct gw_pld {
+	struct gpio_chip chip;
+	struct i2c_client *client;
+	u8 out;
+};
+
+/*
+ * The Gateworks I2C PLD chip only expose one read and one write register.
+ * Writing a "one" bit (to match the reset state) lets that pin be used as an
+ * input. It is an open-drain model.
+ */
+static int gw_pld_input8(struct gpio_chip *gc, unsigned offset)
+{
+	struct gw_pld *gw = gpiochip_get_data(gc);
+
+	gw->out |= BIT(offset);
+	return i2c_smbus_write_byte(gw->client, gw->out);
+}
+
+static int gw_pld_get8(struct gpio_chip *gc, unsigned offset)
+{
+	struct gw_pld *gw = gpiochip_get_data(gc);
+	s32 val;
+
+	val = i2c_smbus_read_byte(gw->client);
+
+	return (val < 0) ? 0 : !!(val & BIT(offset));
+}
+
+static int gw_pld_output8(struct gpio_chip *gc, unsigned offset, int value)
+{
+	struct gw_pld *gw = gpiochip_get_data(gc);
+
+	if (value)
+		gw->out |= BIT(offset);
+	else
+		gw->out &= ~BIT(offset);
+
+	return i2c_smbus_write_byte(gw->client, gw->out);
+}
+
+static void gw_pld_set8(struct gpio_chip *gc, unsigned offset, int value)
+{
+	gw_pld_output8(gc, offset, value);
+}
+
+static int gw_pld_probe(struct i2c_client *client,
+			const struct i2c_device_id *id)
+{
+	struct device *dev = &client->dev;
+	struct device_node *np = dev->of_node;
+	struct gw_pld *gw;
+	int ret;
+
+	gw = devm_kzalloc(dev, sizeof(*gw), GFP_KERNEL);
+	if (!gw)
+		return -ENOMEM;
+
+	gw->chip.base = -1;
+	gw->chip.can_sleep = true;
+	gw->chip.parent = dev;
+	gw->chip.of_node = np;
+	gw->chip.owner = THIS_MODULE;
+	gw->chip.label = dev_name(dev);
+	gw->chip.ngpio = 8;
+	gw->chip.direction_input = gw_pld_input8;
+	gw->chip.get = gw_pld_get8;
+	gw->chip.direction_output = gw_pld_output8;
+	gw->chip.set = gw_pld_set8;
+	gw->client = client;
+
+	/*
+	 * The Gateworks I2C PLD chip does not properly send the acknowledge
+	 * bit at all times, but we can still use the standard i2c_smbus
+	 * functions by simply ignoring this bit.
+	 */
+	client->flags |= I2C_M_IGNORE_NAK;
+	gw->out = 0xFF;
+
+	i2c_set_clientdata(client, gw);
+
+	ret = devm_gpiochip_add_data(dev, &gw->chip, gw);
+	if (ret)
+		return ret;
+
+	dev_info(dev, "registered Gateworks PLD GPIO device\n");
+
+	return 0;
+}
+
+static const struct i2c_device_id gw_pld_id[] = {
+	{ "gw-pld", },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, gw_pld_id);
+
+static const struct of_device_id gw_pld_dt_ids[] = {
+	{ .compatible = "gateworks,pld-gpio", },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, gw_pld_dt_ids);
+
+static struct i2c_driver gw_pld_driver = {
+	.driver = {
+		.name = "gw_pld",
+		.of_match_table = gw_pld_dt_ids,
+	},
+	.probe = gw_pld_probe,
+	.id_table = gw_pld_id,
+};
+module_i2c_driver(gw_pld_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Linus Walleij <linus.walleij@linaro.org>");