i2c: Add detection capability to new-style drivers

Add a mechanism to let new-style i2c drivers optionally autodetect
devices they would support on selected buses and ask i2c-core to
instantiate them. This is a replacement for legacy i2c drivers, much
cleaner.

Where drivers had to implement both a legacy i2c_driver and a
new-style i2c_driver so far, this mechanism makes it possible to get
rid of the legacy i2c_driver and implement both enumerated and
detected device support with just one (new-style) i2c_driver.

Here is a quick conversion guide for these drivers, step by step:

* Delete the legacy driver definition, registration and removal.
  Delete the attach_adapter and detach_client methods of the legacy
  driver.

* Change the prototype of the legacy detect function from
    static int foo_detect(struct i2c_adapter *adapter, int address, int kind);
  to
    static int foo_detect(struct i2c_client *client, int kind,
    			  struct i2c_board_info *info);

* Set the new-style driver detect callback to this new function, and
  set its address_data to &addr_data (addr_data is generally provided
  by I2C_CLIENT_INSMOD.)

* Add the appropriate class to the new-style driver. This is
  typically the class the legacy attach_adapter method was checking
  for. Class checking is now mandatory (done by i2c-core.) See
  <linux/i2c.h> for the list of available classes.

* Remove the i2c_client allocation and freeing from the detect
  function. A pre-allocated client is now handed to you by i2c-core,
  and is freed automatically.

* Make the detect function fill the type field of the i2c_board_info
  structure it was passed as a parameter, and return 0, on success. If
  the detection fails, return -ENODEV.

Signed-off-by: Jean Delvare <khali@linux-fr.org>

1 files changed, 31 insertions, 5 deletions

diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 50cbab4b62b0..08be0d21864c 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -45,6 +45,7 @@ struct i2c_adapter;
 struct i2c_client;
 struct i2c_driver;
 union i2c_smbus_data;
+struct i2c_board_info;
 
 /*
  * The master routines are the ones normally used to transmit data to devices
@@ -94,15 +95,33 @@ extern s32 i2c_smbus_write_i2c_block_data(struct i2c_client * client,
                                           u8 command, u8 length,
                                           const u8 *values);
 
-/*
- * A driver is capable of handling one or more physical devices present on
- * I2C adapters. This information is used to inform the driver of adapter
- * events.
+/**
+ * struct i2c_driver - represent an I2C device driver
+ * @class: What kind of i2c device we instantiate (for detect)
+ * @detect: Callback for device detection
+ * @address_data: The I2C addresses to probe, ignore or force (for detect)
+ * @clients: List of detected clients we created (for i2c-core use only)
  *
  * The driver.owner field should be set to the module owner of this driver.
  * The driver.name field should be set to the name of this driver.
+ *
+ * For automatic device detection, both @detect and @address_data must
+ * be defined. @class should also be set, otherwise only devices forced
+ * with module parameters will be created. The detect function must
+ * fill at least the name field of the i2c_board_info structure it is
+ * handed upon successful detection, and possibly also the flags field.
+ *
+ * If @detect is missing, the driver will still work fine for enumerated
+ * devices. Detected devices simply won't be supported. This is expected
+ * for the many I2C/SMBus devices which can't be detected reliably, and
+ * the ones which can always be enumerated in practice.
+ *
+ * The i2c_client structure which is handed to the @detect callback is
+ * not a real i2c_client. It is initialized just enough so that you can
+ * call i2c_smbus_read_byte_data and friends on it. Don't do anything
+ * else with it. In particular, calling dev_dbg and friends on it is
+ * not allowed.
  */
-
 struct i2c_driver {
         int id;
         unsigned int class;
@@ -142,6 +161,11 @@ struct i2c_driver {
 
         struct device_driver driver;
         const struct i2c_device_id *id_table;
+
+        /* Device detection callback for automatic device creation */
+        int (*detect)(struct i2c_client *, int kind, struct i2c_board_info *);
+        const struct i2c_client_address_data *address_data;
+        struct list_head clients;
 };
 #define to_i2c_driver(d) container_of(d, struct i2c_driver, driver)
 
@@ -157,6 +181,7 @@ struct i2c_driver {
  * @dev: Driver model device node for the slave.
  * @irq: indicates the IRQ generated by this device (if any)
  * @list: list of active/busy clients (DEPRECATED)
+ * @detected: member of an i2c_driver.clients list
  * @released: used to synchronize client releases & detaches and references
  *
  * An i2c_client identifies a single device (i.e. chip) connected to an
@@ -174,6 +199,7 @@ struct i2c_client {
         struct device dev;              /* the device structure         */
         int irq;                        /* irq issued by device         */
         struct list_head list;          /* DEPRECATED */
+        struct list_head detected;
         struct completion released;
 };
 #define to_i2c_client(d) container_of(d, struct i2c_client, dev)