i2c: Documentation: upgrading clients HOWTO

Add a document describing how i2c clients on Linux 2.6 can be
moved from the old to the new driver model.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>

1 files changed, 281 insertions, 0 deletions

diff --git a/Documentation/i2c/upgrading-clients b/Documentation/i2c/upgrading-clients
new file mode 100644
index 000000000000..9a45f9bb6a25
--- /dev/null
+++ b/Documentation/i2c/upgrading-clients
@@ -0,0 +1,281 @@
+Upgrading I2C Drivers to the new 2.6 Driver Model
+=================================================
+
+Ben Dooks <ben-linux@fluff.org>
+
+Introduction
+------------
+
+This guide outlines how to alter existing Linux 2.6 client drivers from
+the old to the new new binding methods.
+
+
+Example old-style driver
+------------------------
+
+
+struct example_state {
+        struct i2c_client       client;
+        ....
+};
+
+static struct i2c_driver example_driver;
+
+static unsigned short ignore[] = { I2C_CLIENT_END };
+static unsigned short normal_addr[] = { OUR_ADDR, I2C_CLIENT_END };
+
+I2C_CLIENT_INSMOD;
+
+static int example_attach(struct i2c_adapter *adap, int addr, int kind)
+{
+        struct example_state *state;
+        struct device *dev = &adap->dev;  /* to use for dev_ reports */
+        int ret;
+
+        state = kzalloc(sizeof(struct example_state), GFP_KERNEL);
+        if (state == NULL) {
+                dev_err(dev, "failed to create our state\n");
+                return -ENOMEM;
+        }
+
+        example->client.addr    = addr;
+        example->client.flags   = 0;
+        example->client.adapter = adap;
+
+        i2c_set_clientdata(&state->i2c_client, state);
+        strlcpy(client->i2c_client.name, "example", I2C_NAME_SIZE);
+
+        ret = i2c_attach_client(&state->i2c_client);
+        if (ret < 0) {
+                dev_err(dev, "failed to attach client\n");
+                kfree(state);
+                return ret;
+        }
+
+        dev = &state->i2c_client.dev;
+
+        /* rest of the initialisation goes here. */
+
+        dev_info(dev, "example client created\n");
+
+        return 0;
+}
+
+static int __devexit example_detach(struct i2c_client *client)
+{
+        struct example_state *state = i2c_get_clientdata(client);
+
+        i2c_detach_client(client);
+        kfree(state);
+        return 0;
+}
+
+static int example_attach_adapter(struct i2c_adapter *adap)
+{
+        return i2c_probe(adap, &addr_data, example_attach);
+}
+
+static struct i2c_driver example_driver = {
+        .driver         = {
+                .owner          = THIS_MODULE,
+                .name           = "example",
+        },
+        .attach_adapter = example_attach_adapter,
+        .detach_client  = __devexit_p(example_detach),
+        .suspend        = example_suspend,
+        .resume         = example_resume,
+};
+
+
+Updating the client
+-------------------
+
+The new style binding model will check against a list of supported
+devices and their associated address supplied by the code registering
+the busses. This means that the driver .attach_adapter and
+.detach_adapter methods can be removed, along with the addr_data,
+as follows:
+
+- static struct i2c_driver example_driver;
+
+- static unsigned short ignore[] = { I2C_CLIENT_END };
+- static unsigned short normal_addr[] = { OUR_ADDR, I2C_CLIENT_END };
+
+- I2C_CLIENT_INSMOD;
+
+- static int example_attach_adapter(struct i2c_adapter *adap)
+- {
+-       return i2c_probe(adap, &addr_data, example_attach);
+- }
+
+ static struct i2c_driver example_driver = {
+-       .attach_adapter = example_attach_adapter,
+-       .detach_client  = __devexit_p(example_detach),
+ }
+
+Add the probe and remove methods to the i2c_driver, as so:
+
+ static struct i2c_driver example_driver = {
++       .probe          = example_probe,
++       .remove         = __devexit_p(example_remove),
+ }
+
+Change the example_attach method to accept the new parameters
+which include the i2c_client that it will be working with:
+
+- static int example_attach(struct i2c_adapter *adap, int addr, int kind)
++ static int example_probe(struct i2c_client *client,
++                          const struct i2c_device_id *id)
+
+Change the name of example_attach to example_probe to align it with the
+i2c_driver entry names. The rest of the probe routine will now need to be
+changed as the i2c_client has already been setup for use.
+
+The necessary client fields have already been setup before
+the probe function is called, so the following client setup
+can be removed:
+
+-       example->client.addr    = addr;
+-       example->client.flags   = 0;
+-       example->client.adapter = adap;
+-
+-       strlcpy(client->i2c_client.name, "example", I2C_NAME_SIZE);
+
+The i2c_set_clientdata is now:
+
+-       i2c_set_clientdata(&state->client, state);
++       i2c_set_clientdata(client, state);
+
+The call to i2c_attach_client is no longer needed, if the probe
+routine exits successfully, then the driver will be automatically
+attached by the core. Change the probe routine as so:
+
+-       ret = i2c_attach_client(&state->i2c_client);
+-       if (ret < 0) {
+-               dev_err(dev, "failed to attach client\n");
+-               kfree(state);
+-               return ret;
+-       }
+
+
+Remove the storage of 'struct i2c_client' from the 'struct example_state'
+as we are provided with the i2c_client in our example_probe. Instead we
+store a pointer to it for when it is needed.
+
+struct example_state {
+-       struct i2c_client       client;
++       struct i2c_client       *client;
+
+the new i2c client as so:
+
+-       struct device *dev = &adap->dev;  /* to use for dev_ reports */
++       struct device *dev = &i2c_client->dev;  /* to use for dev_ reports */
+
+And remove the change after our client is attached, as the driver no
+longer needs to register a new client structure with the core:
+
+-       dev = &state->i2c_client.dev;
+
+In the probe routine, ensure that the new state has the client stored
+in it:
+
+static int example_probe(struct i2c_client *i2c_client,
+                         const struct i2c_device_id *id)
+{
+        struct example_state *state;
+        struct device *dev = &i2c_client->dev;
+        int ret;
+
+        state = kzalloc(sizeof(struct example_state), GFP_KERNEL);
+        if (state == NULL) {
+                dev_err(dev, "failed to create our state\n");
+                return -ENOMEM;
+        }
+
++       state->client = i2c_client;
+
+Update the detach method, by changing the name to _remove and
+to delete the i2c_detach_client call. It is possible that you
+can also remove the ret variable as it is not not needed for
+any of the core functions.
+
+- static int __devexit example_detach(struct i2c_client *client)
++ static int __devexit example_remove(struct i2c_client *client)
+{
+        struct example_state *state = i2c_get_clientdata(client);
+
+-       i2c_detach_client(client);
+
+And finally ensure that we have the correct ID table for the i2c-core
+and other utilities:
+
++ struct i2c_device_id example_idtable[] = {
++       { "example", 0 },
++       { }
++};
++
++MODULE_DEVICE_TABLE(i2c, example_idtable);
+
+static struct i2c_driver example_driver = {
+        .driver         = {
+                .owner          = THIS_MODULE,
+                .name           = "example",
+        },
++       .id_table       = example_ids,
+
+
+Our driver should now look like this:
+
+struct example_state {
+        struct i2c_client       *client;
+        ....
+};
+
+static int example_probe(struct i2c_client *client,
+                         const struct i2c_device_id *id)
+{
+        struct example_state *state;
+        struct device *dev = &client->dev;
+
+        state = kzalloc(sizeof(struct example_state), GFP_KERNEL);
+        if (state == NULL) {
+                dev_err(dev, "failed to create our state\n");
+                return -ENOMEM;
+        }
+
+        state->client = client;
+        i2c_set_clientdata(client, state);
+
+        /* rest of the initialisation goes here. */
+
+        dev_info(dev, "example client created\n");
+
+        return 0;
+}
+
+static int __devexit example_remove(struct i2c_client *client)
+{
+        struct example_state *state = i2c_get_clientdata(client);
+
+        kfree(state);
+        return 0;
+}
+
+static struct i2c_device_id example_idtable[] = {
+        { "example", 0 },
+        { }
+};
+
+MODULE_DEVICE_TABLE(i2c, example_idtable);
+
+static struct i2c_driver example_driver = {
+        .driver         = {
+                .owner          = THIS_MODULE,
+                .name           = "example",
+        },
+        .id_table       = example_idtable,
+        .probe          = example_probe,
+        .remove         = __devexit_p(example_remove),
+        .suspend        = example_suspend,
+        .resume         = example_resume,
+};