Merge branch 'for-linus' of ssh://master.kernel.org/pub/scm/linux/kernel/git/ieee1394...

[pandora-kernel.git] / Documentation / i2c / writing-clients

diff --git a/Documentation/i2c/writing-clients b/Documentation/i2c/writing-clients
index e94d9c6..fbcff96 100644 (file)
--- a/Documentation/i2c/writing-clients
+++ b/Documentation/i2c/writing-clients
@@ -21,24 +21,26 @@ The driver structure
 
 Usually, you will implement a single driver structure, and instantiate
 all clients from it. Remember, a driver structure contains general access 
-routines, a client structure specific information like the actual I2C
-address.
+routines, and should be zero-initialized except for fields with data you
+provide.  A client structure holds device-specific information like the
+driver model device node, and its I2C address.
 
 static struct i2c_driver foo_driver = {
-       .owner          = THIS_MODULE,
-       .name           = "Foo version 2.3 driver",
-       .flags          = I2C_DF_NOTIFY,
-       .attach_adapter = &foo_attach_adapter,
-       .detach_client  = &foo_detach_client,
-       .command        = &foo_command /* may be NULL */
+       .driver = {
+               .name   = "foo",
+       },
+       .attach_adapter = foo_attach_adapter,
+       .detach_client  = foo_detach_client,
+       .shutdown       = foo_shutdown, /* optional */
+       .suspend        = foo_suspend,  /* optional */
+       .resume         = foo_resume,   /* optional */
+       .command        = foo_command,  /* optional */
 }
  
-The name field must match the driver name, including the case. It must not
-contain spaces, and may be up to 31 characters long.
-
-Don't worry about the flags field; just put I2C_DF_NOTIFY into it. This
-means that your driver will be notified when new adapters are found.
-This is almost always what you want.
+The name field is the driver name, and must not contain spaces.  It
+should match the module name (if the driver can be compiled as a module),
+although you can use MODULE_ALIAS (passing "foo" in this example) to add
+another name for the module.
 
 All other fields are for call-back functions which will be explained 
 below.
@@ -47,11 +49,18 @@ below.
 Extra client data
 =================
 
-The client structure has a special `data' field that can point to any
-structure at all. You can use this to keep client-specific data. You
+Each client structure has a special `data' field that can point to any
+structure at all.  You should use this to keep device-specific data,
+especially in drivers that handle multiple I2C or SMBUS devices.  You
 do not always need this, but especially for `sensors' drivers, it can
 be very useful.
 
+       /* store the value */
+       void i2c_set_clientdata(struct i2c_client *client, void *data);
+
+       /* retrieve the value */
+       void *i2c_get_clientdata(struct i2c_client *client);
+
 An example structure is below.
 
   struct foo_data {
@@ -273,6 +282,7 @@ For now, you can ignore the `flags' parameter. It is there for future use.
     if (is_isa) {
 
       /* Discard immediately if this ISA range is already used */
+      /* FIXME: never use check_region(), only request_region() */
       if (check_region(address,FOO_EXTENT))
         goto ERROR0;
 
@@ -411,7 +421,7 @@ For now, you can ignore the `flags' parameter. It is there for future use.
         release_region(address,FOO_EXTENT);
     /* SENSORS ONLY END */
     ERROR1:
-      kfree(new_client);
+      kfree(data);
     ERROR0:
       return err;
   }
@@ -442,7 +452,7 @@ much simpler than the attachment code, fortunately!
       release_region(client->addr,LM78_EXTENT);
     /* HYBRID SENSORS CHIP ONLY END */
 
-    kfree(data);
+    kfree(i2c_get_clientdata(client));
     return 0;
   }
 
@@ -495,17 +505,40 @@ Note that some functions are marked by `__init', and some data structures
 by `__init_data'.  Hose functions and structures can be removed after
 kernel booting (or module loading) is completed.
 
+
+Power Management
+================
+
+If your I2C device needs special handling when entering a system low
+power state -- like putting a transceiver into a low power mode, or
+activating a system wakeup mechanism -- do that in the suspend() method.
+The resume() method should reverse what the suspend() method does.
+
+These are standard driver model calls, and they work just like they
+would for any other driver stack.  The calls can sleep, and can use
+I2C messaging to the device being suspended or resumed (since their
+parent I2C adapter is active when these calls are issued, and IRQs
+are still enabled).
+
+
+System Shutdown
+===============
+
+If your I2C device needs special handling when the system shuts down
+or reboots (including kexec) -- like turning something off -- use a
+shutdown() method.
+
+Again, this is a standard driver model call, working just like it
+would for any other driver stack:  the calls can sleep, and can use
+I2C messaging.
+
+
 Command function
 ================
 
 A generic ioctl-like function call back is supported. You will seldom
-need this. You may even set it to NULL.
-
-  /* No commands defined */
-  int foo_command(struct i2c_client *client, unsigned int cmd, void *arg)
-  {
-    return 0;
-  }
+need this, and its use is deprecated anyway, so newer design should not
+use it. Set it to NULL.
 
 
 Sending and receiving