===============
Try to keep the kernel namespace as clean as possible. The best way to
-do this is to use a unique prefix for all global symbols. This is
+do this is to use a unique prefix for all global symbols. This is
especially important for exported symbols, but it is a good idea to do
it for non-exported symbols too. We will use the prefix `foo_' in this
-tutorial, and `FOO_' for preprocessor variables.
+tutorial.
The driver structure
====================
Usually, you will implement a single driver structure, and instantiate
-all clients from it. Remember, a driver structure contains general access
+all clients from it. Remember, a driver structure contains general access
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.
/* if device autodetection is needed: */
.class = I2C_CLASS_SOMETHING,
.detect = foo_detect,
- .address_data = &addr_data,
+ .address_list = normal_i2c,
.shutdown = foo_shutdown, /* optional */
.suspend = foo_suspend, /* optional */
.resume = foo_resume, /* optional */
- .command = foo_command, /* optional */
+ .command = foo_command, /* optional, deprecated */
}
-
+
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. If the driver name doesn't match the module
name, the module won't be automatically loaded (hotplug/coldplug).
-All other fields are for call-back functions which will be explained
+All other fields are for call-back functions which will be explained
below.
=================
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.
+structure at all. You should use this to keep device-specific data.
/* store the value */
void i2c_set_clientdata(struct i2c_client *client, void *data);
/* retrieve the value */
void *i2c_get_clientdata(const struct i2c_client *client);
-An example structure is below.
-
- struct foo_data {
- struct i2c_client *client;
- enum chips type; /* To keep the chips type for `sensors' drivers. */
-
- /* Because the i2c bus is slow, it is often useful to cache the read
- information of a chip for some time (for example, 1 or 2 seconds).
- It depends of course on the device whether this is really worthwhile
- or even sensible. */
- struct mutex update_lock; /* When we are reading lots of information,
- another process should not update the
- below information */
- char valid; /* != 0 if the following fields are valid. */
- unsigned long last_updated; /* In jiffies */
- /* Add the read information here too */
- };
-
Accessing the client
====================
Let's say we have a valid client structure. At some time, we will need
to gather information from the client, or write new information to the
-client. How we will export this information to user-space is less
-important at this moment (perhaps we do not need to do this at all for
-some obscure clients). But we need generic reading and writing routines.
+client.
-I have found it useful to define foo_read and foo_write function for this.
+I have found it useful to define foo_read and foo_write functions for this.
For some cases, it will be easier to call the i2c functions directly,
but many chips have some kind of register-value idea that can easily
be encapsulated.
The below functions are simple examples, and should not be copied
literally.
- int foo_read_value(struct i2c_client *client, u8 reg)
- {
- if (reg < 0x10) /* byte-sized register */
- return i2c_smbus_read_byte_data(client,reg);
- else /* word-sized register */
- return i2c_smbus_read_word_data(client,reg);
- }
-
- int foo_write_value(struct i2c_client *client, u8 reg, u16 value)
- {
- if (reg == 0x10) /* Impossible to write - driver error! */ {
- return -1;
- else if (reg < 0x10) /* byte-sized register */
- return i2c_smbus_write_byte_data(client,reg,value);
- else /* word-sized register */
- return i2c_smbus_write_word_data(client,reg,value);
- }
+int foo_read_value(struct i2c_client *client, u8 reg)
+{
+ if (reg < 0x10) /* byte-sized register */
+ return i2c_smbus_read_byte_data(client, reg);
+ else /* word-sized register */
+ return i2c_smbus_read_word_data(client, reg);
+}
+
+int foo_write_value(struct i2c_client *client, u8 reg, u16 value)
+{
+ if (reg == 0x10) /* Impossible to write - driver error! */
+ return -EINVAL;
+ else if (reg < 0x10) /* byte-sized register */
+ return i2c_smbus_write_byte_data(client, reg, value);
+ else /* word-sized register */
+ return i2c_smbus_write_word_data(client, reg, value);
+}
Probing and attaching
that can't be distinguished by protocol probing, or which need some board
specific information to operate correctly.
-Accordingly, the I2C stack now has two models for associating I2C devices
-with their drivers: the original "legacy" model, and a newer one that's
-fully compatible with the Linux 2.6 driver model. These models do not mix,
-since the "legacy" model requires drivers to create "i2c_client" device
-objects after SMBus style probing, while the Linux driver model expects
-drivers to be given such device objects in their probe() routines.
-
-The legacy model is deprecated now and will soon be removed, so we no
-longer document it here.
-
-Standard Driver Model Binding ("New Style")
--------------------------------------------
+Device/Driver Binding
+---------------------
System infrastructure, typically board-specific initialization code or
boot firmware, reports what I2C devices exist. For example, there may be
devices on a PC's SMBus. In that case, you may want to let your driver
detect supported devices automatically. This is how the legacy model
was working, and is now available as an extension to the standard
-driver model (so that we can finally get rid of the legacy model.)
+driver model.
You simply have to define a detect callback which will attempt to
identify supported devices (returning 0 for supported ones and -ENODEV
for unsupported ones), a list of addresses to probe, and a device type
(or class) so that only I2C buses which may have that type of device
-connected (and not otherwise enumerated) will be probed. The i2c
-core will then call you back as needed and will instantiate a device
-for you for every successful detection.
+connected (and not otherwise enumerated) will be probed. For example,
+a driver for a hardware monitoring chip for which auto-detection is
+needed would set its class to I2C_CLASS_HWMON, and only I2C adapters
+with a class including I2C_CLASS_HWMON would be probed by this driver.
+Note that the absence of matching classes does not prevent the use of
+a device of that type on the given I2C adapter. All it prevents is
+auto-detection; explicit instantiation of devices is still possible.
Note that this mechanism is purely optional and not suitable for all
devices. You need some reliable way to identify the supported devices
(typically using device-specific, dedicated identification registers),
otherwise misdetections are likely to occur and things can get wrong
-quickly.
+quickly. Keep in mind that the I2C protocol doesn't include any
+standard way to detect the presence of a chip at a given address, let
+alone a standard way to identify devices. Even worse is the lack of
+semantics associated to bus transfers, which means that the same
+transfer can be seen as a read operation by a chip and as a write
+operation by another chip. For these reasons, explicit device
+instantiation should always be preferred to auto-detection where
+possible.
Device Deletion
device can't survive its parent in the device driver model.
-Initializing the module or kernel
-=================================
+Initializing the driver
+=======================
-When the kernel is booted, or when your foo driver module is inserted,
-you have to do some initializing. Fortunately, just attaching (registering)
-the driver module is usually enough.
+When the kernel is booted, or when your foo driver module is inserted,
+you have to do some initializing. Fortunately, just registering the
+driver module is usually enough.
- static int __init foo_init(void)
- {
- int res;
-
- if ((res = i2c_add_driver(&foo_driver))) {
- printk("foo: Driver registration failed, module not inserted.\n");
- return res;
- }
- return 0;
- }
+static int __init foo_init(void)
+{
+ return i2c_add_driver(&foo_driver);
+}
- static void __exit foo_cleanup(void)
- {
- i2c_del_driver(&foo_driver);
- }
+static void __exit foo_cleanup(void)
+{
+ i2c_del_driver(&foo_driver);
+}
- /* Substitute your own name and email address */
- MODULE_AUTHOR("Frodo Looijaard <frodol@dds.nl>"
- MODULE_DESCRIPTION("Driver for Barf Inc. Foo I2C devices");
+/* Substitute your own name and email address */
+MODULE_AUTHOR("Frodo Looijaard <frodol@dds.nl>"
+MODULE_DESCRIPTION("Driver for Barf Inc. Foo I2C devices");
- /* a few non-GPL license types are also allowed */
- MODULE_LICENSE("GPL");
+/* a few non-GPL license types are also allowed */
+MODULE_LICENSE("GPL");
- module_init(foo_init);
- module_exit(foo_cleanup);
+module_init(foo_init);
+module_exit(foo_cleanup);
-Note that some functions are marked by `__init', and some data structures
-by `__initdata'. These functions and structures can be removed after
-kernel booting (or module loading) is completed.
+Note that some functions are marked by `__init'. These functions can
+be removed after kernel booting (or module loading) is completed.
+Likewise, functions marked by `__exit' are dropped by the compiler when
+the code is built into the kernel, as they would never be called.
Power Management
A generic ioctl-like function call back is supported. You will seldom
need this, and its use is deprecated anyway, so newer design should not
-use it. Set it to NULL.
+use it.
Sending and receiving
=====================
If you want to communicate with your device, there are several functions
-to do this. You can find all of them in i2c.h.
+to do this. You can find all of them in <linux/i2c.h>.
-If you can choose between plain i2c communication and SMBus level
-communication, please use the last. All adapters understand SMBus level
-commands, but only some of them understand plain i2c!
+If you can choose between plain I2C communication and SMBus level
+communication, please use the latter. All adapters understand SMBus level
+commands, but only some of them understand plain I2C!
-Plain i2c communication
+Plain I2C communication
-----------------------
- extern int i2c_master_send(struct i2c_client *,const char* ,int);
- extern int i2c_master_recv(struct i2c_client *,char* ,int);
+ int i2c_master_send(struct i2c_client *client, const char *buf,
+ int count);
+ int i2c_master_recv(struct i2c_client *client, char *buf, int count);
These routines read and write some bytes from/to a client. The client
contains the i2c address, so you do not have to include it. The second
-parameter contains the bytes the read/write, the third the length of the
-buffer. Returned is the actual number of bytes read/written.
-
- extern int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msg,
- int num);
+parameter contains the bytes to read/write, the third the number of bytes
+to read/write (must be less than the length of the buffer, also should be
+less than 64k since msg.len is u16.) Returned is the actual number of bytes
+read/written.
+
+ int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msg,
+ int num);
This sends a series of messages. Each message can be a read or write,
and they can be mixed in any way. The transactions are combined: no
and the message data itself.
You can read the file `i2c-protocol' for more information about the
-actual i2c protocol.
+actual I2C protocol.
SMBus communication
-------------------
- extern s32 i2c_smbus_xfer (struct i2c_adapter * adapter, u16 addr,
- unsigned short flags,
- char read_write, u8 command, int size,
- union i2c_smbus_data * data);
-
- This is the generic SMBus function. All functions below are implemented
- in terms of it. Never use this function directly!
-
-
- extern s32 i2c_smbus_read_byte(struct i2c_client * client);
- extern s32 i2c_smbus_write_byte(struct i2c_client * client, u8 value);
- extern s32 i2c_smbus_read_byte_data(struct i2c_client * client, u8 command);
- extern s32 i2c_smbus_write_byte_data(struct i2c_client * client,
- u8 command, u8 value);
- extern s32 i2c_smbus_read_word_data(struct i2c_client * client, u8 command);
- extern s32 i2c_smbus_write_word_data(struct i2c_client * client,
- u8 command, u16 value);
- extern s32 i2c_smbus_process_call(struct i2c_client *client,
- u8 command, u16 value);
- extern s32 i2c_smbus_read_block_data(struct i2c_client * client,
- u8 command, u8 *values);
- extern s32 i2c_smbus_write_block_data(struct i2c_client * client,
- u8 command, u8 length,
- u8 *values);
- extern s32 i2c_smbus_read_i2c_block_data(struct i2c_client * client,
- u8 command, u8 length, u8 *values);
- extern s32 i2c_smbus_write_i2c_block_data(struct i2c_client * client,
- u8 command, u8 length,
- u8 *values);
+ s32 i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
+ unsigned short flags, char read_write, u8 command,
+ int size, union i2c_smbus_data *data);
+
+This is the generic SMBus function. All functions below are implemented
+in terms of it. Never use this function directly!
+
+ s32 i2c_smbus_read_byte(struct i2c_client *client);
+ s32 i2c_smbus_write_byte(struct i2c_client *client, u8 value);
+ s32 i2c_smbus_read_byte_data(struct i2c_client *client, u8 command);
+ s32 i2c_smbus_write_byte_data(struct i2c_client *client,
+ u8 command, u8 value);
+ s32 i2c_smbus_read_word_data(struct i2c_client *client, u8 command);
+ s32 i2c_smbus_write_word_data(struct i2c_client *client,
+ u8 command, u16 value);
+ s32 i2c_smbus_process_call(struct i2c_client *client,
+ u8 command, u16 value);
+ s32 i2c_smbus_read_block_data(struct i2c_client *client,
+ u8 command, u8 *values);
+ s32 i2c_smbus_write_block_data(struct i2c_client *client,
+ u8 command, u8 length, const u8 *values);
+ s32 i2c_smbus_read_i2c_block_data(struct i2c_client *client,
+ u8 command, u8 length, u8 *values);
+ s32 i2c_smbus_write_i2c_block_data(struct i2c_client *client,
+ u8 command, u8 length,
+ const u8 *values);
These ones were removed from i2c-core because they had no users, but could
be added back later if needed:
- extern s32 i2c_smbus_write_quick(struct i2c_client * client, u8 value);
- extern s32 i2c_smbus_block_process_call(struct i2c_client *client,
- u8 command, u8 length,
- u8 *values)
+ s32 i2c_smbus_write_quick(struct i2c_client *client, u8 value);
+ s32 i2c_smbus_block_process_call(struct i2c_client *client,
+ u8 command, u8 length, u8 *values);
All these transactions return a negative errno value on failure. The 'write'
transactions return 0 on success; the 'read' transactions return the read
Below all general purpose routines are listed, that were not mentioned
before.
- /* This call returns a unique low identifier for each registered adapter.
- */
- extern int i2c_adapter_id(struct i2c_adapter *adap);
-
+ /* Return the adapter number for a specific adapter */
+ int i2c_adapter_id(struct i2c_adapter *adap);
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff