i2c: core changes for slave support

Finally(!), make Linux support being an I2C slave. Most of the existing
infrastructure is reused. We mainly add i2c_slave_register/unregister()
calls which tells i2c bus drivers to activate the slave mode. Then, they
also get a callback to report slave events to.

Signed-off-by: Wolfram Sang <[e-mail]>
Signed-off-by: Wolfram Sang <[e-mail]>

drivers/i2c/i2c-core.c

···
    (c) 2013  Wolfram Sang <[e-mail]>
    I2C ACPI code Copyright (C) 2014 Intel Corp
    Author: Lan Tianyu <[e-mail]>
+   I2C slave support (c) 2014 by Wolfram Sang <[e-mail]>
  */
 
 #include <linux/module.h>
···
 	return res;
 }
 EXPORT_SYMBOL(i2c_smbus_xfer);
+
+int i2c_slave_register(struct i2c_client *client, i2c_slave_cb_t slave_cb)
+{
+	int ret;
+
+	if (!client || !slave_cb)
+		return -EINVAL;
+
+	if (!(client->flags & I2C_CLIENT_TEN)) {
+		/* Enforce stricter address checking */
+		ret = i2c_check_addr_validity(client->addr);
+		if (ret)
+			return ret;
+	}
+
+	if (!client->adapter->algo->reg_slave)
+		return -EOPNOTSUPP;
+
+	client->slave_cb = slave_cb;
+
+	i2c_lock_adapter(client->adapter);
+	ret = client->adapter->algo->reg_slave(client);
+	i2c_unlock_adapter(client->adapter);
+
+	if (ret)
+		client->slave_cb = NULL;
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(i2c_slave_register);
+
+int i2c_slave_unregister(struct i2c_client *client)
+{
+	int ret;
+
+	if (!client->adapter->algo->unreg_slave)
+		return -EOPNOTSUPP;
+
+	i2c_lock_adapter(client->adapter);
+	ret = client->adapter->algo->unreg_slave(client);
+	i2c_unlock_adapter(client->adapter);
+
+	if (ret == 0)
+		client->slave_cb = NULL;
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(i2c_slave_unregister);
 
 MODULE_AUTHOR("Simon G. Vogl <[e-mail]>");
 MODULE_DESCRIPTION("I2C-Bus main module");

include/linux/i2c.h

···
 struct i2c_driver;
 union i2c_smbus_data;
 struct i2c_board_info;
+enum i2c_slave_event;
+typedef int (*i2c_slave_cb_t)(struct i2c_client *, enum i2c_slave_event, u8 *);
 
 struct module;
 
···
  * @irq: indicates the IRQ generated by this device (if any)
  * @detected: member of an i2c_driver.clients list or i2c-core's
  *	userspace_devices list
+ * @slave_cb: Callback when I2C slave mode of an adapter is used. The adapter
+ *	calls it to pass on slave events to the slave driver.
  *
  * An i2c_client identifies a single device (i.e. chip) connected to an
  * i2c bus. The behaviour exposed to Linux is defined by the driver
···
 	struct device dev;		/* the device structure		*/
 	int irq;			/* irq issued by device		*/
 	struct list_head detected;
+	i2c_slave_cb_t slave_cb;	/* callback for slave mode	*/
 };
 #define to_i2c_client(d) container_of(d, struct i2c_client, dev)
 
···
 static inline void i2c_set_clientdata(struct i2c_client *dev, void *data)
 {
 	dev_set_drvdata(&dev->dev, data);
+}
+
+/* I2C slave support */
+
+enum i2c_slave_event {
+	I2C_SLAVE_REQ_READ_START,
+	I2C_SLAVE_REQ_READ_END,
+	I2C_SLAVE_REQ_WRITE_START,
+	I2C_SLAVE_REQ_WRITE_END,
+	I2C_SLAVE_STOP,
+};
+
+extern int i2c_slave_register(struct i2c_client *client, i2c_slave_cb_t slave_cb);
+extern int i2c_slave_unregister(struct i2c_client *client);
+
+static inline int i2c_slave_event(struct i2c_client *client,
+				  enum i2c_slave_event event, u8 *val)
+{
+	return client->slave_cb(client, event, val);
 }
 
 /**
···
  *   into I2C transfers instead.
  * @functionality: Return the flags that this algorithm/adapter pair supports
  *   from the I2C_FUNC_* flags.
+ * @reg_slave: Register given client to I2C slave mode of this adapter
+ * @unreg_slave: Unregister given client from I2C slave mode of this adapter
  *
  * The following structs are for those who like to implement new bus drivers:
  * i2c_algorithm is the interface to a class of hardware solutions which can
···
 
 	/* To determine what the adapter supports */
 	u32 (*functionality) (struct i2c_adapter *);
+
+	int (*reg_slave)(struct i2c_client *client);
+	int (*unreg_slave)(struct i2c_client *client);
 };
 
 /**