===============
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.
+static struct i2c_device_id foo_idtable[] = {
+ { "foo", my_id_for_foo },
+ { "bar", my_id_for_bar },
+ { }
+};
+
+MODULE_DEVICE_TABLE(i2c, foo_idtable);
+
static struct i2c_driver foo_driver = {
.driver = {
.name = "foo",
},
- /* iff driver uses driver model ("new style") binding model: */
+ .id_table = foo_ids,
.probe = foo_probe,
.remove = foo_remove,
+ /* if device autodetection is needed: */
+ .class = I2C_CLASS_SOMETHING,
+ .detect = foo_detect,
+ .address_list = normal_i2c,
- /* else, driver uses "legacy" binding model: */
- .attach_adapter = foo_attach_adapter,
- .detach_client = foo_detach_client,
-
- /* these may be used regardless of the driver binding model */
.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(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 */
- };
+ void *i2c_get_clientdata(const struct i2c_client *client);
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
=====================
The Linux I2C stack was originally written to support access to hardware
-monitoring chips on PC motherboards, and thus it embeds some assumptions
-that are more appropriate to SMBus (and PCs) than to I2C. One of these
-assumptions is that most adapters and devices drivers support the SMBUS_QUICK
-protocol to probe device presence. Another is that devices and their drivers
+monitoring chips on PC motherboards, and thus used to embed some assumptions
+that were more appropriate to SMBus (and PCs) than to I2C. One of these
+assumptions was that most adapters and devices drivers support the SMBUS_QUICK
+protocol to probe device presence. Another was that devices and their drivers
can be sufficiently configured using only such probe primitives.
As Linux and its I2C stack became more widely used in embedded systems
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.
-
-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
kind of driver in Linux: they provide a probe() method to bind to
those devices, and a remove() method to unbind.
- static int foo_probe(struct i2c_client *client);
+ static int foo_probe(struct i2c_client *client,
+ const struct i2c_device_id *id);
static int foo_remove(struct i2c_client *client);
Remember that the i2c_driver does not create those client handles. The
(zero not a negative status code) it may save the handle and use it until
foo_remove() returns. That binding model is used by most Linux drivers.
-Drivers match devices when i2c_client.driver_name and the driver name are
-the same; this approach is used in several other busses that don't have
-device typing support in the hardware. The driver and module name should
-match, so hotplug/coldplug mechanisms will modprobe the driver.
+The probe function is called when an entry in the id_table name field
+matches the device's name. It is passed the entry that was matched so
+the driver knows which one in the table matched.
-Device Creation (Standard driver model)
----------------------------------------
+Device Creation
+---------------
If you know for a fact that an I2C device is connected to a given I2C bus,
you can instantiate that device by simply filling an i2c_board_info
reference for later use.
-Device Deletion (Standard driver model)
----------------------------------------
+Device Detection
+----------------
+
+Sometimes you do not know in advance which I2C devices are connected to
+a given I2C bus. This is for example the case of hardware monitoring
+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.
+
+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. 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. 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
+---------------
Each I2C device which has been created using i2c_new_device() or
i2c_new_probed_device() can be unregistered by calling
device can't survive its parent in the device driver model.
-Legacy Driver Binding Model
----------------------------
+Initializing the driver
+=======================
+
+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.
-Most i2c devices can be present on several i2c addresses; for some this
-is determined in hardware (by soldering some chip pins to Vcc or Ground),
-for others this can be changed in software (by writing to specific client
-registers). Some devices are usually on a specific address, but not always;
-and some are even more tricky. So you will probably need to scan several
-i2c addresses for your clients, and do some sort of detection to see
-whether it is actually a device supported by your driver.
+static int __init foo_init(void)
+{
+ return i2c_add_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");
+
+/* a few non-GPL license types are also allowed */
+MODULE_LICENSE("GPL");
-To give the user a maximum of possibilities, some default module parameters
-are defined to help determine what addresses are scanned. Several macros
-are defined in i2c.h to help you support them, as well as a generic
-detection algorithm.
-
-You do not have to use this parameter interface; but don't try to use
-function i2c_probe() if you don't.
-
-
-Probing classes (Legacy model)
-------------------------------
-
-All parameters are given as lists of unsigned 16-bit integers. Lists are
-terminated by I2C_CLIENT_END.
-The following lists are used internally:
-
- normal_i2c: filled in by the module writer.
- A list of I2C addresses which should normally be examined.
- probe: insmod parameter.
- A list of pairs. The first value is a bus number (-1 for any I2C bus),
- the second is the address. These addresses are also probed, as if they
- were in the 'normal' list.
- ignore: insmod parameter.
- A list of pairs. The first value is a bus number (-1 for any I2C bus),
- the second is the I2C address. These addresses are never probed.
- This parameter overrules the 'normal_i2c' list only.
- force: insmod parameter.
- A list of pairs. The first value is a bus number (-1 for any I2C bus),
- the second is the I2C address. A device is blindly assumed to be on
- the given address, no probing is done.
-
-Additionally, kind-specific force lists may optionally be defined if
-the driver supports several chip kinds. They are grouped in a
-NULL-terminated list of pointers named forces, those first element if the
-generic force list mentioned above. Each additional list correspond to an
-insmod parameter of the form force_<kind>.
-
-Fortunately, as a module writer, you just have to define the `normal_i2c'
-parameter. The complete declaration could look like this:
-
- /* Scan 0x37, and 0x48 to 0x4f */
- static unsigned short normal_i2c[] = { 0x37, 0x48, 0x49, 0x4a, 0x4b, 0x4c,
- 0x4d, 0x4e, 0x4f, I2C_CLIENT_END };
-
- /* Magic definition of all other variables and things */
- I2C_CLIENT_INSMOD;
- /* Or, if your driver supports, say, 2 kind of devices: */
- I2C_CLIENT_INSMOD_2(foo, bar);
-
-If you use the multi-kind form, an enum will be defined for you:
- enum chips { any_chip, foo, bar, ... }
-You can then (and certainly should) use it in the driver code.
-
-Note that you *have* to call the defined variable `normal_i2c',
-without any prefix!
-
-
-Attaching to an adapter (Legacy model)
---------------------------------------
-
-Whenever a new adapter is inserted, or for all adapters if the driver is
-being registered, the callback attach_adapter() is called. Now is the
-time to determine what devices are present on the adapter, and to register
-a client for each of them.
-
-The attach_adapter callback is really easy: we just call the generic
-detection function. This function will scan the bus for us, using the
-information as defined in the lists explained above. If a device is
-detected at a specific address, another callback is called.
-
- int foo_attach_adapter(struct i2c_adapter *adapter)
- {
- return i2c_probe(adapter,&addr_data,&foo_detect_client);
- }
-
-Remember, structure `addr_data' is defined by the macros explained above,
-so you do not have to define it yourself.
-
-The i2c_probe function will call the foo_detect_client
-function only for those i2c addresses that actually have a device on
-them (unless a `force' parameter was used). In addition, addresses that
-are already in use (by some other registered client) are skipped.
-
-
-The detect client function (Legacy model)
------------------------------------------
-
-The detect client function is called by i2c_probe. The `kind' parameter
-contains -1 for a probed detection, 0 for a forced detection, or a positive
-number for a forced detection with a chip type forced.
-
-Returning an error different from -ENODEV in a detect function will cause
-the detection to stop: other addresses and adapters won't be scanned.
-This should only be done on fatal or internal errors, such as a memory
-shortage or i2c_attach_client failing.
-
-For now, you can ignore the `flags' parameter. It is there for future use.
-
- int foo_detect_client(struct i2c_adapter *adapter, int address,
- int kind)
- {
- int err = 0;
- int i;
- struct i2c_client *client;
- struct foo_data *data;
- const char *name = "";
-
- /* Let's see whether this adapter can support what we need.
- Please substitute the things you need here! */
- if (!i2c_check_functionality(adapter,I2C_FUNC_SMBUS_WORD_DATA |
- I2C_FUNC_SMBUS_WRITE_BYTE))
- goto ERROR0;
-
- /* OK. For now, we presume we have a valid client. We now create the
- client structure, even though we cannot fill it completely yet.
- But it allows us to access several i2c functions safely */
-
- if (!(data = kzalloc(sizeof(struct foo_data), GFP_KERNEL))) {
- err = -ENOMEM;
- goto ERROR0;
- }
-
- client = &data->client;
- i2c_set_clientdata(client, data);
-
- client->addr = address;
- client->adapter = adapter;
- client->driver = &foo_driver;
-
- /* Now, we do the remaining detection. If no `force' parameter is used. */
-
- /* First, the generic detection (if any), that is skipped if any force
- parameter was used. */
- if (kind < 0) {
- /* The below is of course bogus */
- if (foo_read(client, FOO_REG_GENERIC) != FOO_GENERIC_VALUE)
- goto ERROR1;
- }
-
- /* Next, specific detection. This is especially important for `sensors'
- devices. */
-
- /* Determine the chip type. Not needed if a `force_CHIPTYPE' parameter
- was used. */
- if (kind <= 0) {
- i = foo_read(client, FOO_REG_CHIPTYPE);
- if (i == FOO_TYPE_1)
- kind = chip1; /* As defined in the enum */
- else if (i == FOO_TYPE_2)
- kind = chip2;
- else {
- printk("foo: Ignoring 'force' parameter for unknown chip at "
- "adapter %d, address 0x%02x\n",i2c_adapter_id(adapter),address);
- goto ERROR1;
- }
- }
-
- /* Now set the type and chip names */
- if (kind == chip1) {
- name = "chip1";
- } else if (kind == chip2) {
- name = "chip2";
- }
-
- /* Fill in the remaining client fields. */
- strlcpy(client->name, name, I2C_NAME_SIZE);
- data->type = kind;
- mutex_init(&data->update_lock); /* Only if you use this field */
-
- /* Any other initializations in data must be done here too. */
-
- /* This function can write default values to the client registers, if
- needed. */
- foo_init_client(client);
-
- /* Tell the i2c layer a new client has arrived */
- if ((err = i2c_attach_client(client)))
- goto ERROR1;
-
- return 0;
-
- /* OK, this is not exactly good programming practice, usually. But it is
- very code-efficient in this case. */
-
- ERROR1:
- kfree(data);
- ERROR0:
- return err;
- }
-
-
-Removing the client (Legacy model)
-==================================
-
-The detach_client call back function is called when a client should be
-removed. It may actually fail, but only when panicking. This code is
-much simpler than the attachment code, fortunately!
-
- int foo_detach_client(struct i2c_client *client)
- {
- int err;
-
- /* Try to detach the client from i2c space */
- if ((err = i2c_detach_client(client)))
- return err;
-
- kfree(i2c_get_clientdata(client));
- return 0;
- }
-
-
-Initializing the module or kernel
-=================================
-
-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.
-
- 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 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");
-
- /* a few non-GPL license types are also allowed */
- MODULE_LICENSE("GPL");
-
- 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.
+module_init(foo_init);
+module_exit(foo_cleanup);
+
+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.) 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_write_quick(struct i2c_client * client, u8 value);
- 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_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 *values);
-
-These ones were removed in Linux 2.6.10 because they had no users, but could
+ 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_read_block_data(struct i2c_client * client,
- u8 command, u8 *values);
- extern s32 i2c_smbus_write_i2c_block_data(struct i2c_client * client,
- u8 command, u8 length,
- u8 *values);
- extern s32 i2c_smbus_process_call(struct i2c_client * client,
- u8 command, u16 value);
- extern s32 i2c_smbus_block_process_call(struct i2c_client *client,
- u8 command, u8 length,
- u8 *values)
-
-All these transactions return -1 on failure. The 'write' transactions
-return 0 on success; the 'read' transactions return the read value, except
-for read_block, which returns the number of values read. The block buffers
-need not be longer than 32 bytes.
+ 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
+value, except for block transactions, which return the number of values
+read. The block buffers need not be longer than 32 bytes.
You can read the file `smbus-protocol' for more information about the
actual SMBus protocol.
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);
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