dm: i2c: add i2c-gpio driver

This commit adds driver model support to software emulated i2c bus driver.
This driver supports kernel-style device tree bindings. Fdt properties in use:
- compatible - "i2c-gpio"
- gpios      - data and clock GPIO pin phandles
- delay-us   - micro seconds delay between GPIOs toggle operations,
               which is 1/4 of I2C speed clock period.

Added:
- Config: CONFIG_DM_I2C_GPIO
- File: drivers/i2c/i2c-gpio.c
- File: doc/device-tree-bindings/i2c/i2c-gpio.txt

Driver base code is taken from: drivers/i2c/soft-i2c.c, changes:
- use "i2c-gpio" naming
- update comments style
- move preprocesor macros into functions
- add device tree support
- add driver model i2c support
- code cleanup,
- add Kconfig entry

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>
Added braces in i2c_gpio_xfer() to fix style nit:
Signed-off-by: Simon Glass <sjg@chromium.org>

doc/device-tree-bindings/i2c/i2c-gpio.txt

@@ -0,0 +1,37 @@
+I2C gpio device binding
+=======================
+
+Driver:
+- drivers/i2c/i2c-gpio.c
+
+Software i2c device-tree node properties:
+Required:
+* #address-cells = <1>;
+* #size-cells = <0>;
+* compatible = "i2c-gpio";
+* gpios = <sda ...>, <scl ...>;
+
+Optional:
+* i2c-gpio,delay-us = <5>;
+   The resulting transfer speed can be adjusted by setting the delay[us]
+   between gpio-toggle operations. Speed [Hz] = 1000000 / 4 * udelay[us],
+   It not defined, then default is 5us (~50KHz).
+
+Example:
+
+i2c-gpio@1 {
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	compatible = "i2c-gpio";
+	gpios = <&gpd1 0 GPIO_ACTIVE_HIGH>, /* SDA */
+		<&gpd1 1 GPIO_ACTIVE_HIGH>; /* CLK */
+
+	i2c-gpio,delay-us = <5>;
+
+	some_device@5 {
+		compatible = "some_device";
+		reg = <0x5>;
+		...
+	};
+};

drivers/i2c/Kconfig

@@ -19,6 +19,15 @@ config DM_I2C_COMPAT
 	  to convert all code for a board in a single commit. It should not
 	  be enabled for any board in an official release.
 
+config DM_I2C_GPIO
+	bool "Enable Driver Model for software emulated I2C bus driver"
+	depends on DM_I2C && DM_GPIO
+	help
+	  Enable the i2c bus driver emulation by using the GPIOs. The bus GPIO
+	  configuration is given by the device tree. Kernel-style device tree
+	  bindings are supported.
+	  Binding info: doc/device-tree-bindings/i2c/i2c-gpio.txt
+
 config SYS_I2C_UNIPHIER
 	bool "UniPhier I2C driver"
 	depends on ARCH_UNIPHIER && DM_I2C

drivers/i2c/Makefile

@@ -6,6 +6,7 @@
 #
 obj-$(CONFIG_DM_I2C) += i2c-uclass.o
 obj-$(CONFIG_DM_I2C_COMPAT) += i2c-uclass-compat.o
+obj-$(CONFIG_DM_I2C_GPIO) += i2c-gpio.o
 
 obj-$(CONFIG_SYS_I2C_ADI) += adi_i2c.o
 obj-$(CONFIG_I2C_MV) += mv_i2c.o

drivers/i2c/i2c-gpio.c

@@ -0,0 +1,346 @@
+/*
+ * (C) Copyright 2015, Samsung Electronics
+ * Przemyslaw Marczak <p.marczak@samsung.com>
+ *
+ * This file is based on: drivers/i2c/soft-i2c.c,
+ * with added driver-model support and code cleanup.
+ */
+#include <common.h>
+#include <errno.h>
+#include <dm.h>
+#include <i2c.h>
+#include <asm/gpio.h>
+
+#define DEFAULT_UDELAY	5
+#define RETRIES		0
+#define I2C_ACK		0
+#define I2C_NOACK	1
+
+DECLARE_GLOBAL_DATA_PTR;
+
+enum {
+	PIN_SDA = 0,
+	PIN_SCL,
+	PIN_COUNT,
+};
+
+struct i2c_gpio_bus {
+	/**
+	  * udelay - delay [us] between GPIO toggle operations,
+	  * which is 1/4 of I2C speed clock period.
+	 */
+	int udelay;
+	 /* sda, scl */
+	struct gpio_desc gpios[PIN_COUNT];
+};
+
+static int i2c_gpio_sda_get(struct gpio_desc *sda)
+{
+	return dm_gpio_get_value(sda);
+}
+
+static void i2c_gpio_sda_set(struct gpio_desc *sda, int bit)
+{
+	if (bit) {
+		dm_gpio_set_dir_flags(sda, GPIOD_IS_IN);
+	} else {
+		dm_gpio_set_dir_flags(sda, GPIOD_IS_OUT);
+		dm_gpio_set_value(sda, 0);
+	}
+}
+
+static void i2c_gpio_scl_set(struct gpio_desc *scl, int bit)
+{
+	dm_gpio_set_dir_flags(scl, GPIOD_IS_OUT);
+	dm_gpio_set_value(scl, bit);
+}
+
+static void i2c_gpio_write_bit(struct gpio_desc *scl, struct gpio_desc *sda,
+			       int delay, uchar bit)
+{
+	i2c_gpio_scl_set(scl, 0);
+	udelay(delay);
+	i2c_gpio_sda_set(sda, bit);
+	udelay(delay);
+	i2c_gpio_scl_set(scl, 1);
+	udelay(2 * delay);
+}
+
+static int i2c_gpio_read_bit(struct gpio_desc *scl, struct gpio_desc *sda,
+			     int delay)
+{
+	int value;
+
+	i2c_gpio_scl_set(scl, 1);
+	udelay(delay);
+	value = i2c_gpio_sda_get(sda);
+	udelay(delay);
+	i2c_gpio_scl_set(scl, 0);
+	udelay(2 * delay);
+
+	return value;
+}
+
+/* START: High -> Low on SDA while SCL is High */
+static void i2c_gpio_send_start(struct gpio_desc *scl, struct gpio_desc *sda,
+				int delay)
+{
+	udelay(delay);
+	i2c_gpio_sda_set(sda, 1);
+	udelay(delay);
+	i2c_gpio_scl_set(scl, 1);
+	udelay(delay);
+	i2c_gpio_sda_set(sda, 0);
+	udelay(delay);
+}
+
+/* STOP: Low -> High on SDA while SCL is High */
+static void i2c_gpio_send_stop(struct gpio_desc *scl, struct gpio_desc *sda,
+			       int delay)
+{
+	i2c_gpio_scl_set(scl, 0);
+	udelay(delay);
+	i2c_gpio_sda_set(sda, 0);
+	udelay(delay);
+	i2c_gpio_scl_set(scl, 1);
+	udelay(delay);
+	i2c_gpio_sda_set(sda, 1);
+	udelay(delay);
+}
+
+/* ack should be I2C_ACK or I2C_NOACK */
+static void i2c_gpio_send_ack(struct gpio_desc *scl, struct gpio_desc *sda,
+			      int delay, int ack)
+{
+	i2c_gpio_write_bit(scl, sda, delay, ack);
+	i2c_gpio_scl_set(scl, 0);
+	udelay(delay);
+}
+
+/**
+ * Send a reset sequence consisting of 9 clocks with the data signal high
+ * to clock any confused device back into an idle state.  Also send a
+ * <stop> at the end of the sequence for belts & suspenders.
+ */
+static void i2c_gpio_send_reset(struct gpio_desc *scl, struct gpio_desc *sda,
+				int delay)
+{
+	int j;
+
+	for (j = 0; j < 9; j++)
+		i2c_gpio_write_bit(scl, sda, delay, 1);
+
+	i2c_gpio_send_stop(scl, sda, delay);
+}
+
+/* Set sda high with low clock, before reading slave data */
+static void i2c_gpio_sda_high(struct gpio_desc *scl, struct gpio_desc *sda,
+			      int delay)
+{
+	i2c_gpio_scl_set(scl, 0);
+	udelay(delay);
+	i2c_gpio_sda_set(sda, 1);
+	udelay(delay);
+}
+
+/* Send 8 bits and look for an acknowledgement */
+static int i2c_gpio_write_byte(struct gpio_desc *scl, struct gpio_desc *sda,
+			       int delay, uchar data)
+{
+	int j;
+	int nack;
+
+	for (j = 0; j < 8; j++) {
+		i2c_gpio_write_bit(scl, sda, delay, data & 0x80);
+		data <<= 1;
+	}
+
+	udelay(delay);
+
+	/* Look for an <ACK>(negative logic) and return it */
+	i2c_gpio_sda_high(scl, sda, delay);
+	nack = i2c_gpio_read_bit(scl, sda, delay);
+
+	return nack;	/* not a nack is an ack */
+}
+
+/**
+ * if ack == I2C_ACK, ACK the byte so can continue reading, else
+ * send I2C_NOACK to end the read.
+ */
+static uchar i2c_gpio_read_byte(struct gpio_desc *scl, struct gpio_desc *sda,
+				int delay, int ack)
+{
+	int  data;
+	int  j;
+
+	i2c_gpio_sda_high(scl, sda, delay);
+	data = 0;
+	for (j = 0; j < 8; j++) {
+		data <<= 1;
+		data |= i2c_gpio_read_bit(scl, sda, delay);
+	}
+	i2c_gpio_send_ack(scl, sda, delay, ack);
+
+	return data;
+}
+
+/* send start and the slave chip address */
+int i2c_send_slave_addr(struct gpio_desc *scl, struct gpio_desc *sda, int delay,
+			uchar chip)
+{
+	i2c_gpio_send_start(scl, sda, delay);
+
+	if (i2c_gpio_write_byte(scl, sda, delay, chip)) {
+		i2c_gpio_send_stop(scl, sda, delay);
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int i2c_gpio_write_data(struct i2c_gpio_bus *bus, uchar chip,
+			       uchar *buffer, int len,
+			       bool end_with_repeated_start)
+{
+	struct gpio_desc *scl = &bus->gpios[PIN_SCL];
+	struct gpio_desc *sda = &bus->gpios[PIN_SDA];
+	unsigned int delay = bus->udelay;
+	int failures = 0;
+
+	debug("%s: chip %x buffer %p len %d\n", __func__, chip, buffer, len);
+
+	if (i2c_send_slave_addr(scl, sda, delay, chip << 1)) {
+		debug("i2c_write, no chip responded %02X\n", chip);
+		return -EIO;
+	}
+
+	while (len-- > 0) {
+		if (i2c_gpio_write_byte(scl, sda, delay, *buffer++))
+			failures++;
+	}
+
+	if (!end_with_repeated_start) {
+		i2c_gpio_send_stop(scl, sda, delay);
+		return failures;
+	}
+
+	if (i2c_send_slave_addr(scl, sda, delay, (chip << 1) | 0x1)) {
+		debug("i2c_write, no chip responded %02X\n", chip);
+		return -EIO;
+	}
+
+	return failures;
+}
+
+static int i2c_gpio_read_data(struct i2c_gpio_bus *bus, uchar chip,
+			      uchar *buffer, int len)
+{
+	struct gpio_desc *scl = &bus->gpios[PIN_SCL];
+	struct gpio_desc *sda = &bus->gpios[PIN_SDA];
+	unsigned int delay = bus->udelay;
+
+	debug("%s: chip %x buffer: %p len %d\n", __func__, chip, buffer, len);
+
+	while (len-- > 0)
+		*buffer++ = i2c_gpio_read_byte(scl, sda, delay, len == 0);
+
+	i2c_gpio_send_stop(scl, sda, delay);
+
+	return 0;
+}
+
+static int i2c_gpio_xfer(struct udevice *dev, struct i2c_msg *msg, int nmsgs)
+{
+	struct i2c_gpio_bus *bus = dev_get_priv(dev);
+	int ret;
+
+	for (; nmsgs > 0; nmsgs--, msg++) {
+		bool next_is_read = nmsgs > 1 && (msg[1].flags & I2C_M_RD);
+
+		if (msg->flags & I2C_M_RD) {
+			ret = i2c_gpio_read_data(bus, msg->addr, msg->buf,
+						 msg->len);
+		} else {
+			ret = i2c_gpio_write_data(bus, msg->addr, msg->buf,
+						  msg->len, next_is_read);
+		}
+
+		if (ret)
+			return -EREMOTEIO;
+	}
+
+	return 0;
+}
+
+static int i2c_gpio_probe(struct udevice *dev, uint chip, uint chip_flags)
+{
+	struct i2c_gpio_bus *bus = dev_get_priv(dev);
+	struct gpio_desc *scl = &bus->gpios[PIN_SCL];
+	struct gpio_desc *sda = &bus->gpios[PIN_SDA];
+	unsigned int delay = bus->udelay;
+	int ret;
+
+	i2c_gpio_send_start(scl, sda, delay);
+	ret = i2c_gpio_write_byte(scl, sda, delay, (chip << 1) | 0);
+	i2c_gpio_send_stop(scl, sda, delay);
+
+	debug("%s: bus: %d (%s) chip: %x flags: %x ret: %d\n",
+	      __func__, dev->seq, dev->name, chip, chip_flags, ret);
+
+	return ret;
+}
+
+static int i2c_gpio_set_bus_speed(struct udevice *dev, unsigned int speed_hz)
+{
+	struct i2c_gpio_bus *bus = dev_get_priv(dev);
+	struct gpio_desc *scl = &bus->gpios[PIN_SCL];
+	struct gpio_desc *sda = &bus->gpios[PIN_SDA];
+
+	bus->udelay = 1000000 / (speed_hz << 2);
+
+	i2c_gpio_send_reset(scl, sda, bus->udelay);
+
+	return 0;
+}
+
+static int i2c_gpio_ofdata_to_platdata(struct udevice *dev)
+{
+	struct i2c_gpio_bus *bus = dev_get_priv(dev);
+	const void *blob = gd->fdt_blob;
+	int node = dev->of_offset;
+	int ret;
+
+	ret = gpio_request_list_by_name(dev, "gpios", bus->gpios,
+					ARRAY_SIZE(bus->gpios), 0);
+	if (ret < 0)
+		goto error;
+
+	bus->udelay = fdtdec_get_int(blob, node, "i2c-gpio,delay-us",
+				     DEFAULT_UDELAY);
+
+	return 0;
+error:
+	error("Can't get %s gpios! Error: %d", dev->name, ret);
+	return ret;
+}
+
+static const struct dm_i2c_ops i2c_gpio_ops = {
+	.xfer		= i2c_gpio_xfer,
+	.probe_chip	= i2c_gpio_probe,
+	.set_bus_speed	= i2c_gpio_set_bus_speed,
+};
+
+static const struct udevice_id i2c_gpio_ids[] = {
+	{ .compatible = "i2c-gpio" },
+	{ }
+};
+
+U_BOOT_DRIVER(i2c_gpio) = {
+	.name	= "i2c-gpio",
+	.id	= UCLASS_I2C,
+	.of_match = i2c_gpio_ids,
+	.ofdata_to_platdata = i2c_gpio_ofdata_to_platdata,
+	.priv_auto_alloc_size = sizeof(struct i2c_gpio_bus),
+	.ops	= &i2c_gpio_ops,
+};