i2c: muxes: add i2c gpio multiplexer driver

Add an i2c mux driver providing access to i2c bus segments using a
hardware MUX sitting on a master bus and controlled through gpio pins.

E.G. something like:

         ----------              ----------  Bus segment 1   - - - - -
        |          | SCL/SDA    |          |-------------- |           |
        |          |------------|          |
        |          |            |          | Bus segment 2 |           |
        |  Linux   | GPIO 1..N  |   MUX    |---------------   Devices
        |          |------------|          |               |           |
        |          |            |          | Bus segment M
        |          |            |          |---------------|           |
         ----------              ----------                  - - - - -

SCL/SDA of the master I2C bus is multiplexed to bus segment 1..M
according to the settings of the GPIO pins 1..N.

Note commit log from kernel
commit 92ed1a76("i2c: Add generic I2C multiplexer using GPIO API")

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Tested-by: Peng Fan <peng.fan@nxp.com> (i.MX6QP-Sabreauto)
Cc: Heiko Schocher <hs@denx.de>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Simon Glass <sjg@chromium.org>

drivers/i2c/muxes/Kconfig

@@ -34,3 +34,12 @@ config I2C_MUX_PCA954x
 	  paritioning I2C bus and connect multiple devices with the same address
 	  to the same I2C controller where driver handles proper routing to
 	  target i2c device. PCA9544 and PCA9548 are supported.
+
+config I2C_MUX_GPIO
+        tristate "GPIO-based I2C multiplexer"
+	depends on I2C_MUX && DM_GPIO
+	help
+	  If you say yes to this option, support will be included for
+	  a GPIO based I2C multiplexer. This driver provides access to
+	  I2C busses connected through a MUX, which is controlled
+	  through GPIO pins.

drivers/i2c/muxes/Makefile

@@ -6,3 +6,4 @@
 obj-$(CONFIG_I2C_ARB_GPIO_CHALLENGE) += i2c-arb-gpio-challenge.o
 obj-$(CONFIG_$(SPL_)I2C_MUX) += i2c-mux-uclass.o
 obj-$(CONFIG_I2C_MUX_PCA954x) += pca954x.o
+obj-$(CONFIG_I2C_MUX_GPIO) += i2c-mux-gpio.o

drivers/i2c/muxes/i2c-mux-gpio.c

@@ -0,0 +1,138 @@
+/*
+ * I2C multiplexer using GPIO API
+ *
+ * Copyright 2017 NXP
+ *
+ * Peng Fan <peng.fan@nxp.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <asm/io.h>
+#include <asm-generic/gpio.h>
+#include <common.h>
+#include <dm.h>
+#include <dm/pinctrl.h>
+#include <fdtdec.h>
+#include <i2c.h>
+#include <linux/errno.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+/**
+ * struct i2c_mux_gpio_priv - private data for i2c mux gpio
+ *
+ * @values: the reg value of each child node
+ * @n_values: num of regs
+ * @gpios: the mux-gpios array
+ * @n_gpios: num of gpios in mux-gpios
+ * @idle: the value of idle-state
+ */
+struct i2c_mux_gpio_priv {
+	u32 *values;
+	int n_values;
+	struct gpio_desc *gpios;
+	int n_gpios;
+	u32 idle;
+};
+
+
+static int i2c_mux_gpio_select(struct udevice *dev, struct udevice *bus,
+			       uint channel)
+{
+	struct i2c_mux_gpio_priv *priv = dev_get_priv(dev);
+	int i, ret;
+
+	for (i = 0; i < priv->n_gpios; i++) {
+		ret = dm_gpio_set_value(&priv->gpios[i], (channel >> i) & 1);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int i2c_mux_gpio_deselect(struct udevice *dev, struct udevice *bus,
+				 uint channel)
+{
+	struct i2c_mux_gpio_priv *priv = dev_get_priv(dev);
+	int i, ret;
+
+	for (i = 0; i < priv->n_gpios; i++) {
+		ret = dm_gpio_set_value(&priv->gpios[i], (priv->idle >> i) & 1);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int i2c_mux_gpio_probe(struct udevice *dev)
+{
+	const void *fdt = gd->fdt_blob;
+	int node = dev_of_offset(dev);
+	struct i2c_mux_gpio_priv *mux = dev_get_priv(dev);
+	struct gpio_desc *gpios;
+	u32 *values;
+	int i = 0, subnode, ret;
+
+	mux->n_values = fdtdec_get_child_count(fdt, node);
+	values = devm_kzalloc(dev, sizeof(*mux->values) * mux->n_values,
+			      GFP_KERNEL);
+	if (!values) {
+		dev_err(dev, "Cannot alloc values array");
+		return -ENOMEM;
+	}
+
+	fdt_for_each_subnode(subnode, fdt, node) {
+		*(values + i) = fdtdec_get_uint(fdt, subnode, "reg", -1);
+		i++;
+	}
+
+	mux->values = values;
+
+	mux->idle = fdtdec_get_uint(fdt, node, "idle-state", -1);
+
+	mux->n_gpios = gpio_get_list_count(dev, "mux-gpios");
+	if (mux->n_gpios < 0) {
+		dev_err(dev, "Missing mux-gpios property\n");
+		return -EINVAL;
+	}
+
+	gpios = devm_kzalloc(dev, sizeof(struct gpio_desc) * mux->n_gpios,
+			     GFP_KERNEL);
+	if (!gpios) {
+		dev_err(dev, "Cannot allocate gpios array\n");
+		return -ENOMEM;
+	}
+
+	ret = gpio_request_list_by_name(dev, "mux-gpios", gpios, mux->n_gpios,
+					GPIOD_IS_OUT_ACTIVE);
+	if (ret <= 0) {
+		dev_err(dev, "Failed to request mux-gpios\n");
+		return ret;
+	}
+
+	mux->gpios = gpios;
+
+	return 0;
+}
+
+static const struct i2c_mux_ops i2c_mux_gpio_ops = {
+	.select = i2c_mux_gpio_select,
+	.deselect = i2c_mux_gpio_deselect,
+};
+
+static const struct udevice_id i2c_mux_gpio_ids[] = {
+	{ .compatible = "i2c-mux-gpio", },
+	{}
+};
+
+U_BOOT_DRIVER(i2c_mux_gpio) = {
+	.name = "i2c_mux_gpio",
+	.id = UCLASS_I2C_MUX,
+	.of_match = i2c_mux_gpio_ids,
+	.ops = &i2c_mux_gpio_ops,
+	.probe = i2c_mux_gpio_probe,
+	.priv_auto_alloc_size = sizeof(struct i2c_mux_gpio_priv),
+};