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i2c: Documentation update

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Make the documentation on how to write and port i2c drivers more in
line with the current state of things:
* i2c-isa is deprecated and soon gone, so stop advertising it.
* Drop many sensors-specific references. Most of them were outdated
  anyway.
* Update the example code to reflect the recent and not-so-recent
  API and coding style preference changes.
* Simplify the example init and cleanup functions.

This should make things less complex to understand for newcomers.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
This commit is contained in:
Jean Delvare
2007-05-01 23:26:35 +02:00
committed by Jean Delvare
parent 35532d2003
commit eefcd75e72
2 changed files with 39 additions and 271 deletions
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292
Documentation/i2c/writing-clients
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@@ -74,16 +74,13 @@ 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. */
@@ -104,8 +101,7 @@ some obscure clients). But we need generic reading and writing routines.
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.
@@ -128,24 +124,6 @@ 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
=====================
@@ -257,10 +235,6 @@ detection algorithm.
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)
------------------------------
@@ -344,10 +318,6 @@ 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
@@ -356,64 +326,20 @@ 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,
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 */
@@ -423,13 +349,12 @@ For now, you can ignore the `flags' parameter. It is there for future use.
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. */
@@ -437,19 +362,17 @@ For now, you can ignore the `flags' parameter. It is there for future use.
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)
@@ -463,63 +386,31 @@ For now, you can ignore the `flags' parameter. It is there for future use.
/* 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:
@@ -536,22 +427,12 @@ much simpler than the attachment code, fortunately!
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;
}
@@ -564,42 +445,34 @@ 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.
/* 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 --;
}
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.
@@ -729,110 +602,7 @@ General purpose routines
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]);
}
}
}