i2c: Documentation update

Revision 6, 2005-11-20

Revision 7, 2007-04-19

Jean Delvare <khali@linux-fr.org>

Greg KH <greg@kroah.com>

Technical changes:

* [Driver type] Any driver that was relying on i2c-isa has to be

  converted to a proper isa, platform or pci driver. This is not

  covered by this guide.

* [Includes] Get rid of "version.h" and <linux/i2c-proc.h>.

  Includes typically look like that:

  #include <linux/module.h>

  #include <linux/slab.h>

  #include <linux/jiffies.h>

  #include <linux/i2c.h>

  #include <linux/i2c-isa.h>	/* for ISA drivers */

  #include <linux/hwmon.h>	/* for hardware monitoring drivers */

  #include <linux/hwmon-sysfs.h>

  #include <linux/hwmon-vid.h>	/* if you need VRM support */

  #include <linux/err.h>	/* for class registration */

  #include <asm/io.h>		/* if you have I/O operations */

  Please respect this inclusion order. Some extra headers may be

  required for a given driver (e.g. "lm75.h").

  sensors mailing list <lm-sensors@lm-sensors.org> by providing a

  patch to the Documentation/hwmon/sysfs-interface file.

* [Attach] For I2C drivers, the attach function should make sure

  that the adapter's class has I2C_CLASS_HWMON (or whatever class is

  suitable for your driver), using the following construct:

* [Attach] The attach function should make sure that the adapter's

  class has I2C_CLASS_HWMON (or whatever class is suitable for your

  driver), using the following construct:

  if (!(adapter->class & I2C_CLASS_HWMON))

          return 0;

  ISA-only drivers of course don't need this.

  Call i2c_probe() instead of i2c_detect().

* [Detect] As mentioned earlier, the flags parameter is gone.

  The type_name and client_name strings are replaced by a single

  name string, which will be filled with a lowercase, short string.

  In i2c-only drivers, drop the i2c_is_isa_adapter check, it's

  useless. Same for isa-only drivers, as the test would always be

  true. Only hybrid drivers (which are quite rare) still need it.

  The labels used for error paths are reduced to the number needed.

  It is advised that the labels are given descriptive names such as

  exit and exit_free. Don't forget to properly set err before

  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

=====================

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 (Legacy model)

------------------------------

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:

  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) {

    i2c_del_driver(&foo_driver);

      foo_initialized --;

    }

  }

  /* 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.

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]);

      }

    }

  }