This is a small guide for those who want to write kernel drivers for I2C
-or SMBus devices.
+or SMBus devices, using Linux as the protocol host/master (not slave).
To set up a driver, you need to do several things. Some are optional, and
some things can be done slightly or completely different. Use this as a
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",
+ },
+
+ /* iff driver uses driver model ("new style") binding model: */
+ .probe = foo_probe,
+ .remove = foo_remove,
+
+ /* 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 */
}
-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. 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
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 {
struct i2c_client client;
- struct semaphore lock; /* For ISA access in `sensors' drivers. */
- int sysctl_id; /* To keep the /proc directory entry for
- `sensors' drivers. */
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 semaphore update_lock; /* When we are reading lots of information,
+ 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. */
I have found it useful to define foo_read and foo_write function 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. Also, some chips have both ISA and I2C interfaces, and
-it useful to abstract from this (only for `sensors' drivers).
+be encapsulated.
The below functions are simple examples, and should not be copied
literally.
return i2c_smbus_write_word_data(client,reg,value);
}
-For sensors code, you may have to cope with ISA registers too. Something
-like the below often works. Note the locking!
-
- int foo_read_value(struct i2c_client *client, u8 reg)
- {
- int res;
- if (i2c_is_isa_client(client)) {
- down(&(((struct foo_data *) (client->data)) -> lock));
- outb_p(reg,client->addr + FOO_ADDR_REG_OFFSET);
- res = inb_p(client->addr + FOO_DATA_REG_OFFSET);
- up(&(((struct foo_data *) (client->data)) -> lock));
- return res;
- } else
- return i2c_smbus_read_byte_data(client,reg);
- }
-
-Writing is done the same way.
-
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
+can be sufficiently configured using only such probe primitives.
+
+As Linux and its I2C stack became more widely used in embedded systems
+and complex components such as DVB adapters, those assumptions became more
+problematic. Drivers for I2C devices that issue interrupts need more (and
+different) configuration information, as do drivers handling chip variants
+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")
+-------------------------------------------
+
+System infrastructure, typically board-specific initialization code or
+boot firmware, reports what I2C devices exist. For example, there may be
+a table, in the kernel or from the boot loader, identifying I2C devices
+and linking them to board-specific configuration information about IRQs
+and other wiring artifacts, chip type, and so on. That could be used to
+create i2c_client objects for each I2C device.
+
+I2C device drivers using this binding model work just like any other
+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_remove(struct i2c_client *client);
+
+Remember that the i2c_driver does not create those client handles. The
+handle may be used during foo_probe(). If foo_probe() reports success
+(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.
+
+
+Device Creation (Standard driver model)
+---------------------------------------
+
+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
+structure with the device address and driver name, and calling
+i2c_new_device(). This will create the device, then the driver core will
+take care of finding the right driver and will call its probe() method.
+If a driver supports different device types, you can specify the type you
+want using the type field. You can also specify an IRQ and platform data
+if needed.
+
+Sometimes you know that a device is connected to a given I2C bus, but you
+don't know the exact address it uses. This happens on TV adapters for
+example, where the same driver supports dozens of slightly different
+models, and I2C device addresses change from one model to the next. In
+that case, you can use the i2c_new_probed_device() variant, which is
+similar to i2c_new_device(), except that it takes an additional list of
+possible I2C addresses to probe. A device is created for the first
+responsive address in the list. If you expect more than one device to be
+present in the address range, simply call i2c_new_probed_device() that
+many times.
+
+The call to i2c_new_device() or i2c_new_probed_device() typically happens
+in the I2C bus driver. You may want to save the returned i2c_client
+reference for later use.
+
+
+Device Deletion (Standard driver model)
+---------------------------------------
+
+Each I2C device which has been created using i2c_new_device() or
+i2c_new_probed_device() can be unregistered by calling
+i2c_unregister_device(). If you don't call it explicitly, it will be
+called automatically before the underlying I2C bus itself is removed, as a
+device can't survive its parent in the device driver model.
+
+
+Legacy Driver Binding Model
+---------------------------
+
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
You do not have to use this parameter interface; but don't try to use
function i2c_probe() if you don't.
-NOTE: If you want to write a `sensors' driver, the interface is slightly
- different! See below.
-
-
-Probing classes
----------------
+Probing classes (Legacy model)
+------------------------------
All parameters are given as lists of unsigned 16-bit integers. Lists are
terminated by I2C_CLIENT_END.
without any prefix!
-Attaching to an adapter
------------------------
+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
are already in use (by some other registered client) are skipped.
-The detect client function
---------------------------
+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.
-Below, some things are only needed if this is a `sensors' driver. Those
-parts are between /* SENSORS ONLY START */ and /* SENSORS ONLY END */
-markers.
-
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
For now, you can ignore the `flags' parameter. It is there for future use.
int foo_detect_client(struct i2c_adapter *adapter, int address,
- unsigned short flags, int kind)
+ int kind)
{
int err = 0;
int i;
- struct i2c_client *new_client;
+ struct i2c_client *client;
struct foo_data *data;
- const char *client_name = ""; /* For non-`sensors' drivers, put the real
- name here! */
+ const char *name = "";
/* Let's see whether this adapter can support what we need.
- Please substitute the things you need here!
- For `sensors' drivers, add `! is_isa &&' to the if statement */
+ Please substitute the things you need here! */
if (!i2c_check_functionality(adapter,I2C_FUNC_SMBUS_WORD_DATA |
I2C_FUNC_SMBUS_WRITE_BYTE))
goto ERROR0;
- /* SENSORS ONLY START */
- const char *type_name = "";
- int is_isa = i2c_is_isa_adapter(adapter);
-
- /* Do this only if the chip can additionally be found on the ISA bus
- (hybrid chip). */
-
- 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;
-
- /* Probe whether there is anything on this address.
- Some example code is below, but you will have to adapt this
- for your own driver */
-
- if (kind < 0) /* Only if no force parameter was used */ {
- /* We may need long timeouts at least for some chips. */
- #define REALLY_SLOW_IO
- i = inb_p(address + 1);
- if (inb_p(address + 2) != i)
- goto ERROR0;
- if (inb_p(address + 3) != i)
- goto ERROR0;
- if (inb_p(address + 7) != i)
- goto ERROR0;
- #undef REALLY_SLOW_IO
-
- /* Let's just hope nothing breaks here */
- i = inb_p(address + 5) & 0x7f;
- outb_p(~i & 0x7f,address+5);
- if ((inb_p(address + 5) & 0x7f) != (~i & 0x7f)) {
- outb_p(i,address+5);
- return 0;
- }
- }
- }
-
- /* SENSORS ONLY END */
-
/* 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 */
goto ERROR0;
}
- new_client = &data->client;
- i2c_set_clientdata(new_client, data);
+ client = &data->client;
+ i2c_set_clientdata(client, data);
- new_client->addr = address;
- new_client->adapter = adapter;
- new_client->driver = &foo_driver;
- new_client->flags = 0;
+ client->addr = address;
+ client->adapter = adapter;
+ client->driver = &foo_driver;
/* Now, we do the remaining detection. If no `force' parameter is used. */
parameter was used. */
if (kind < 0) {
/* The below is of course bogus */
- if (foo_read(new_client,FOO_REG_GENERIC) != FOO_GENERIC_VALUE)
+ if (foo_read(client, FOO_REG_GENERIC) != FOO_GENERIC_VALUE)
goto ERROR1;
}
- /* SENSORS ONLY START */
-
/* 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(new_client,FOO_REG_CHIPTYPE);
+ 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)
/* Now set the type and chip names */
if (kind == chip1) {
- type_name = "chip1"; /* For /proc entry */
- client_name = "CHIP 1";
+ name = "chip1";
} else if (kind == chip2) {
- type_name = "chip2"; /* For /proc entry */
- client_name = "CHIP 2";
+ name = "chip2";
}
- /* Reserve the ISA region */
- if (is_isa)
- request_region(address,FOO_EXTENT,type_name);
-
- /* SENSORS ONLY END */
-
/* Fill in the remaining client fields. */
- strcpy(new_client->name,client_name);
-
- /* SENSORS ONLY BEGIN */
+ strlcpy(client->name, name, I2C_NAME_SIZE);
data->type = kind;
- /* SENSORS ONLY END */
-
- data->valid = 0; /* Only if you use this field */
- init_MUTEX(&data->update_lock); /* Only if you use this field */
+ mutex_init(&data->update_lock); /* Only if you use this field */
/* Any other initializations in data must be done here too. */
- /* Tell the i2c layer a new client has arrived */
- if ((err = i2c_attach_client(new_client)))
- goto ERROR3;
-
- /* SENSORS ONLY BEGIN */
- /* Register a new directory entry with module sensors. See below for
- the `template' structure. */
- if ((i = i2c_register_entry(new_client, type_name,
- foo_dir_table_template,THIS_MODULE)) < 0) {
- err = i;
- goto ERROR4;
- }
- data->sysctl_id = i;
-
- /* SENSORS ONLY END */
-
/* This function can write default values to the client registers, if
needed. */
- foo_init_client(new_client);
+ 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. */
- ERROR4:
- i2c_detach_client(new_client);
- ERROR3:
- ERROR2:
- /* SENSORS ONLY START */
- if (is_isa)
- release_region(address,FOO_EXTENT);
- /* SENSORS ONLY END */
ERROR1:
kfree(data);
ERROR0:
}
-Removing the client
-===================
+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
int foo_detach_client(struct i2c_client *client)
{
- int err,i;
-
- /* SENSORS ONLY START */
- /* Deregister with the `i2c-proc' module. */
- i2c_deregister_entry(((struct lm78_data *)(client->data))->sysctl_id);
- /* SENSORS ONLY END */
+ int err;
/* Try to detach the client from i2c space */
if ((err = i2c_detach_client(client)))
return err;
- /* HYBRID SENSORS CHIP ONLY START */
- if i2c_is_isa_client(client)
- release_region(client->addr,LM78_EXTENT);
- /* HYBRID SENSORS CHIP ONLY END */
-
kfree(i2c_get_clientdata(client));
return 0;
}
you have to do some initializing. Fortunately, just attaching (registering)
the driver module is usually enough.
- /* Keep track of how far we got in the initialization process. If several
- things have to initialized, and we fail halfway, only those things
- have to be cleaned up! */
- static int __initdata foo_initialized = 0;
-
static int __init foo_init(void)
{
int res;
- printk("foo version %s (%s)\n",FOO_VERSION,FOO_DATE);
if ((res = i2c_add_driver(&foo_driver))) {
printk("foo: Driver registration failed, module not inserted.\n");
- foo_cleanup();
return res;
}
- foo_initialized ++;
return 0;
}
- void foo_cleanup(void)
+ static void __exit foo_cleanup(void)
{
- if (foo_initialized == 1) {
- if ((res = i2c_del_driver(&foo_driver))) {
- printk("foo: Driver registration failed, module not removed.\n");
- return;
- }
- foo_initialized --;
- }
+ 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 `__init_data'. Hose functions and structures can be removed after
+by `__initdata'. These 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
Below all general purpose routines are listed, that were not mentioned
before.
- /* This call returns a unique low identifier for each registered adapter,
- * or -1 if the adapter was not registered.
+ /* This call returns a unique low identifier for each registered adapter.
*/
extern int i2c_adapter_id(struct i2c_adapter *adap);
-
-The sensors sysctl/proc interface
-=================================
-
-This section only applies if you write `sensors' drivers.
-
-Each sensors driver creates a directory in /proc/sys/dev/sensors for each
-registered client. The directory is called something like foo-i2c-4-65.
-The sensors module helps you to do this as easily as possible.
-
-The template
-------------
-
-You will need to define a ctl_table template. This template will automatically
-be copied to a newly allocated structure and filled in where necessary when
-you call sensors_register_entry.
-
-First, I will give an example definition.
- static ctl_table foo_dir_table_template[] = {
- { FOO_SYSCTL_FUNC1, "func1", NULL, 0, 0644, NULL, &i2c_proc_real,
- &i2c_sysctl_real,NULL,&foo_func },
- { FOO_SYSCTL_FUNC2, "func2", NULL, 0, 0644, NULL, &i2c_proc_real,
- &i2c_sysctl_real,NULL,&foo_func },
- { FOO_SYSCTL_DATA, "data", NULL, 0, 0644, NULL, &i2c_proc_real,
- &i2c_sysctl_real,NULL,&foo_data },
- { 0 }
- };
-
-In the above example, three entries are defined. They can either be
-accessed through the /proc interface, in the /proc/sys/dev/sensors/*
-directories, as files named func1, func2 and data, or alternatively
-through the sysctl interface, in the appropriate table, with identifiers
-FOO_SYSCTL_FUNC1, FOO_SYSCTL_FUNC2 and FOO_SYSCTL_DATA.
-
-The third, sixth and ninth parameters should always be NULL, and the
-fourth should always be 0. The fifth is the mode of the /proc file;
-0644 is safe, as the file will be owned by root:root.
-
-The seventh and eighth parameters should be &i2c_proc_real and
-&i2c_sysctl_real if you want to export lists of reals (scaled
-integers). You can also use your own function for them, as usual.
-Finally, the last parameter is the call-back to gather the data
-(see below) if you use the *_proc_real functions.
-
-
-Gathering the data
-------------------
-
-The call back functions (foo_func and foo_data in the above example)
-can be called in several ways; the operation parameter determines
-what should be done:
-
- * If operation == SENSORS_PROC_REAL_INFO, you must return the
- magnitude (scaling) in nrels_mag;
- * If operation == SENSORS_PROC_REAL_READ, you must read information
- from the chip and return it in results. The number of integers
- to display should be put in nrels_mag;
- * If operation == SENSORS_PROC_REAL_WRITE, you must write the
- supplied information to the chip. nrels_mag will contain the number
- of integers, results the integers themselves.
-
-The *_proc_real functions will display the elements as reals for the
-/proc interface. If you set the magnitude to 2, and supply 345 for
-SENSORS_PROC_REAL_READ, it would display 3.45; and if the user would
-write 45.6 to the /proc file, it would be returned as 4560 for
-SENSORS_PROC_REAL_WRITE. A magnitude may even be negative!
-
-An example function:
-
- /* FOO_FROM_REG and FOO_TO_REG translate between scaled values and
- register values. Note the use of the read cache. */
- void foo_in(struct i2c_client *client, int operation, int ctl_name,
- int *nrels_mag, long *results)
- {
- struct foo_data *data = client->data;
- int nr = ctl_name - FOO_SYSCTL_FUNC1; /* reduce to 0 upwards */
-
- if (operation == SENSORS_PROC_REAL_INFO)
- *nrels_mag = 2;
- else if (operation == SENSORS_PROC_REAL_READ) {
- /* Update the readings cache (if necessary) */
- foo_update_client(client);
- /* Get the readings from the cache */
- results[0] = FOO_FROM_REG(data->foo_func_base[nr]);
- results[1] = FOO_FROM_REG(data->foo_func_more[nr]);
- results[2] = FOO_FROM_REG(data->foo_func_readonly[nr]);
- *nrels_mag = 2;
- } else if (operation == SENSORS_PROC_REAL_WRITE) {
- if (*nrels_mag >= 1) {
- /* Update the cache */
- data->foo_base[nr] = FOO_TO_REG(results[0]);
- /* Update the chip */
- foo_write_value(client,FOO_REG_FUNC_BASE(nr),data->foo_base[nr]);
- }
- if (*nrels_mag >= 2) {
- /* Update the cache */
- data->foo_more[nr] = FOO_TO_REG(results[1]);
- /* Update the chip */
- foo_write_value(client,FOO_REG_FUNC_MORE(nr),data->foo_more[nr]);
- }
- }
- }
git.samba.org / sfrench / cifs-2.6.git / blobdiff