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Commit 92b42946 authored by Jean Delvare's avatar Jean Delvare Committed by Greg Kroah-Hartman
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[PATCH] i2c: Chip driver porting guide update 



Update Documentation/i2c/porting-clients. Many recent changes to the i2c
and hwmon subsystems were never reported there.

Signed-off-by: default avatarJean Delvare <khali@linux-fr.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent cf02df77

Documentation/i2c/porting-clients

+44 −35
Original line number Original line Diff line number Diff line 
Revision 5, 2005-07-29

Revision 6, 2005-11-20

Jean Delvare <khali@linux-fr.org>

Jean Delvare <khali@linux-fr.org>

Greg KH <greg@kroah.com>

Greg KH <greg@kroah.com>





This is a guide on how to convert I2C chip drivers from Linux 2.4 to

This is a guide on how to convert I2C chip drivers from Linux 2.4 to

Linux 2.6. I have been using existing drivers (lm75, lm78) as examples.

Linux 2.6. I have been using existing drivers (lm75, lm78) as examples.

Then I converted a driver myself (lm83) and updated this document.

Then I converted a driver myself (lm83) and updated this document.

Note that this guide is strongly oriented towards hardware monitoring

drivers. Many points are still valid for other type of drivers, but

others may be irrelevant.





There are two sets of points below. The first set concerns technical

There are two sets of points below. The first set concerns technical

changes. The second set concerns coding policy. Both are mandatory.

changes. The second set concerns coding policy. Both are mandatory.
@@ -22,16 +25,20 @@ Technical changes: 
  #include <linux/module.h>

  #include <linux/module.h>

  #include <linux/init.h>

  #include <linux/init.h>

  #include <linux/slab.h>

  #include <linux/slab.h>

  #include <linux/jiffies.h>

  #include <linux/i2c.h>

  #include <linux/i2c.h>

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

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

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

  #include <linux/hwmon-sysfs.h>

  #include <linux/hwmon-sysfs.h>

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

  #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 */

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

  Please respect this inclusion order. Some extra headers may be

  Please respect this inclusion order. Some extra headers may be

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

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





* [Addresses] SENSORS_I2C_END becomes I2C_CLIENT_END, ISA addresses

* [Addresses] SENSORS_I2C_END becomes I2C_CLIENT_END, ISA addresses

  are no more handled by the i2c core.

  are no more handled by the i2c core. Address ranges are no more

  supported either, define each individual address separately.

  SENSORS_INSMOD_<n> becomes I2C_CLIENT_INSMOD_<n>.

  SENSORS_INSMOD_<n> becomes I2C_CLIENT_INSMOD_<n>.





* [Client data] Get rid of sysctl_id. Try using standard names for

* [Client data] Get rid of sysctl_id. Try using standard names for
@@ -48,23 +55,23 @@ Technical changes: 
      int kind);

      int kind);

  static void lm75_init_client(struct i2c_client *client);

  static void lm75_init_client(struct i2c_client *client);

  static int lm75_detach_client(struct i2c_client *client);

  static int lm75_detach_client(struct i2c_client *client);

  static void lm75_update_client(struct i2c_client *client);

  static struct lm75_data lm75_update_device(struct device *dev);





* [Sysctl] All sysctl stuff is of course gone (defines, ctl_table

* [Sysctl] All sysctl stuff is of course gone (defines, ctl_table

  and functions). Instead, you have to define show and set functions for

  and functions). Instead, you have to define show and set functions for

  each sysfs file. Only define set for writable values. Take a look at an

  each sysfs file. Only define set for writable values. Take a look at an

  existing 2.6 driver for details (lm78 for example). Don't forget

  existing 2.6 driver for details (it87 for example). Don't forget

  to define the attributes for each file (this is that step that

  to define the attributes for each file (this is that step that

  links callback functions). Use the file names specified in

  links callback functions). Use the file names specified in

  Documentation/i2c/sysfs-interface for the individual files. Also

  Documentation/hwmon/sysfs-interface for the individual files. Also

  convert the units these files read and write to the specified ones.

  convert the units these files read and write to the specified ones.

  If you need to add a new type of file, please discuss it on the

  If you need to add a new type of file, please discuss it on the

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

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

  patch to the Documentation/i2c/sysfs-interface file.

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





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

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

  that the adapter's class has I2C_CLASS_HWMON, using the

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

  following construct:

  suitable for your driver), using the following construct:

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

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

          return 0;

          return 0;

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

  ISA-only drivers of course don't need this.
@@ -72,23 +79,23 @@ Technical changes: 




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

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

  The type_name and client_name strings are replaced by a single

  The type_name and client_name strings are replaced by a single

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

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

  (typically the driver name, e.g. "lm75").

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

  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

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

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

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

  The errorN labels are reduced to the number needed. If that number

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

  is 2 (i2c-only drivers), it is advised that the labels are named

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

  exit and exit_free. For i2c+isa drivers, labels should be named

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

  ERROR0, ERROR1 and ERROR2. Don't forget to properly set err before

  jumping to error labels. By the way, labels should be left-aligned.

  jumping to error labels. By the way, labels should be left-aligned.

  Use kzalloc instead of kmalloc.

  Use kzalloc instead of kmalloc.

  Use i2c_set_clientdata to set the client data (as opposed to

  Use i2c_set_clientdata to set the client data (as opposed to

  a direct access to client->data).

  a direct access to client->data).

  Use strlcpy instead of strcpy to copy the client name.

  Use strlcpy instead of strcpy or snprintf to copy the client name.

  Replace the sysctl directory registration by calls to

  Replace the sysctl directory registration by calls to

  device_create_file. Move the driver initialization before any

  device_create_file. Move the driver initialization before any

  sysfs file creation.

  sysfs file creation.

  Register the client with the hwmon class (using hwmon_device_register)

  if applicable.

  Drop client->id.

  Drop client->id.

  Drop any 24RF08 corruption prevention you find, as this is now done

  Drop any 24RF08 corruption prevention you find, as this is now done

  at the i2c-core level, and doing it twice voids it.

  at the i2c-core level, and doing it twice voids it.
@@ -96,19 +103,25 @@ Technical changes: 




* [Init] Limits must not be set by the driver (can be done later in

* [Init] Limits must not be set by the driver (can be done later in

  user-space). Chip should not be reset default (although a module

  user-space). Chip should not be reset default (although a module

  parameter may be used to force is), and initialization should be

  parameter may be used to force it), and initialization should be

  limited to the strictly necessary steps.

  limited to the strictly necessary steps.





* [Detach] Get rid of data, remove the call to

* [Detach] Remove the call to i2c_deregister_entry. Do not log an

  i2c_deregister_entry. Do not log an error message if

  error message if i2c_detach_client fails, as i2c-core will now do

  i2c_detach_client fails, as i2c-core will now do it for you.

  it for you.

  Unregister from the hwmon class if applicable.





* [Update] Don't access client->data directly, use

* [Update] The function prototype changed, it is now

  i2c_get_clientdata(client) instead.

  passed a device structure, which you have to convert to a client

  using to_i2c_client(dev). The update function should return a

  pointer to the client data.

  Don't access client->data directly, use i2c_get_clientdata(client)

  instead.

  Use time_after() instead of direct jiffies comparison.





* [Interface] Init function should not print anything. Make sure

* [Interface] Make sure there is a MODULE_LICENSE() line, at the bottom

  there is a MODULE_LICENSE() line, at the bottom of the file

  of the file (after MODULE_AUTHOR() and MODULE_DESCRIPTION(), in this

  (after MODULE_AUTHOR() and MODULE_DESCRIPTION(), in this order).

  order).





* [Driver] The flags field of the i2c_driver structure is gone.

* [Driver] The flags field of the i2c_driver structure is gone.

  I2C_DF_NOTIFY is now the default behavior.

  I2C_DF_NOTIFY is now the default behavior.
@@ -118,21 +131,17 @@ Coding policy: 
* [Copyright] Use (C), not (c), for copyright.

* [Copyright] Use (C), not (c), for copyright.





* [Debug/log] Get rid of #ifdef DEBUG/#endif constructs whenever you

* [Debug/log] Get rid of #ifdef DEBUG/#endif constructs whenever you

  can. Calls to printk/pr_debug for debugging purposes are replaced

  can. Calls to printk for debugging purposes are replaced by calls to

  by calls to dev_dbg. Here is an example on how to call it (taken

  dev_dbg where possible, else to pr_debug. Here is an example of how

  from lm75_detect):

  to call it (taken from lm75_detect):

  dev_dbg(&client->dev, "Starting lm75 update\n");

  dev_dbg(&client->dev, "Starting lm75 update\n");

  Replace other printk calls with the dev_info, dev_err or dev_warn

  Replace other printk calls with the dev_info, dev_err or dev_warn

  function, as appropriate.

  function, as appropriate.





* [Constants] Constants defines (registers, conversions, initial

* [Constants] Constants defines (registers, conversions) should be

  values) should be aligned. This greatly improves readability.

  aligned. This greatly improves readability.

  Same goes for variables declarations. Alignments are achieved by the

  Alignments are achieved by the means of tabs, not spaces. Remember

  means of tabs, not spaces. Remember that tabs are set to 8 in the

  that tabs are set to 8 in the Linux kernel code.

  Linux kernel code.



* [Structure definition] The name field should be standardized. All

  lowercase and as simple as the driver name itself (e.g. "lm75").





* [Layout] Avoid extra empty lines between comments and what they

* [Layout] Avoid extra empty lines between comments and what they

  comment. Respect the coding style (see Documentation/CodingStyle),

  comment. Respect the coding style (see Documentation/CodingStyle),