i2c: Delete outdated client porting guide

The document describing how to port i2c chip drivers from Linux 2.4 to
Linux 2.6 is outdated. As I suspect that most drivers that had to be
ported have already been by now, I do not want to spend time updating
it. Let's just delete it instead.
Signed-off-by: Jean Delvare <khali@linux-fr.org>

Documentation/i2c/porting-clients

-Revision 7, 2007-04-19
-Jean Delvare <khali@linux-fr.org>
-Greg KH <greg@kroah.com>
-
-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.
-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
-changes. The second set concerns coding policy. Both are mandatory.
-
-Although reading this guide will help you porting drivers, I suggest
-you keep an eye on an already ported driver while porting your own
-driver. This will help you a lot understanding what this guide
-exactly means. Choose the chip driver that is the more similar to
-yours for best results.
-
-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/init.h>
-  #include <linux/slab.h>
-  #include <linux/jiffies.h>
-  #include <linux/i2c.h>
-  #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 */
-  Please respect this inclusion order. Some extra headers may be
-  required for a given driver (e.g. "lm75.h").
-
-* [Addresses] SENSORS_I2C_END becomes I2C_CLIENT_END, ISA addresses
-  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>.
-
-* [Client data] Get rid of sysctl_id. Try using standard names for
-  register values (for example, temp_os becomes temp_max). You're
-  still relatively free here, but you *have* to follow the standard
-  names for sysfs files (see the Sysctl section below).
-
-* [Function prototypes] The detect functions loses its flags
-  parameter. Sysctl (e.g. lm75_temp) and miscellaneous functions
-  are off the list of prototypes. This usually leaves five
-  prototypes:
-  static int lm75_attach_adapter(struct i2c_adapter *adapter);
-  static int lm75_detect(struct i2c_adapter *adapter, int address,
-      int kind);
-  static void lm75_init_client(struct i2c_client *client);
-  static int lm75_detach_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
-  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
-  existing 2.6 driver for details (it87 for example). Don't forget
-  to define the attributes for each file (this is that step that
-  links callback functions). Use the file names specified in
-  Documentation/hwmon/sysfs-interface for the individual files. Also
-  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
-  sensors mailing list <lm-sensors@lm-sensors.org> by providing a
-  patch to the Documentation/hwmon/sysfs-interface file.
-
-* [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;
-  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.
-  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
-  jumping to error labels. By the way, labels should be left-aligned.
-  Use kzalloc instead of kmalloc.
-  Use i2c_set_clientdata to set the client data (as opposed to
-  a direct access to client->data).
-  Use strlcpy instead of strcpy or snprintf to copy the client name.
-  Replace the sysctl directory registration by calls to
-  device_create_file. Move the driver initialization before any
-  sysfs file creation.
-  Register the client with the hwmon class (using hwmon_device_register)
-  if applicable.
-  Drop client->id.
-  Drop any 24RF08 corruption prevention you find, as this is now done
-  at the i2c-core level, and doing it twice voids it.
-  Don't add I2C_CLIENT_ALLOW_USE to client->flags, it's the default now.
-
-* [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
-  parameter may be used to force it), and initialization should be
-  limited to the strictly necessary steps.
-
-* [Detach] Remove the call to i2c_deregister_entry. Do not log an
-  error message if i2c_detach_client fails, as i2c-core will now do
-  it for you.
-  Unregister from the hwmon class if applicable.
-
-* [Update] The function prototype changed, it is now
-  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] Make sure there is a MODULE_LICENSE() line, at the bottom
-  of the file (after MODULE_AUTHOR() and MODULE_DESCRIPTION(), in this
-  order).
-
-* [Driver] The flags field of the i2c_driver structure is gone.
-  I2C_DF_NOTIFY is now the default behavior.
-  The i2c_driver structure has a driver member, which is itself a
-  structure, those name member should be initialized to a driver name
-  string. i2c_driver itself has no name member anymore.
-
-* [Driver model] Instead of shutdown or reboot notifiers, provide a
-  shutdown() method in your driver.
-
-* [Power management] Use the driver model suspend() and resume()
-  callbacks instead of the obsolete pm_register() calls.
-
-Coding policy:
-
-* [Copyright] Use (C), not (c), for copyright.
-
-* [Debug/log] Get rid of #ifdef DEBUG/#endif constructs whenever you
-  can. Calls to printk for debugging purposes are replaced by calls to
-  dev_dbg where possible, else to pr_debug. Here is an example of how
-  to call it (taken from lm75_detect):
-  dev_dbg(&client->dev, "Starting lm75 update\n");
-  Replace other printk calls with the dev_info, dev_err or dev_warn
-  function, as appropriate.
-
-* [Constants] Constants defines (registers, conversions) should be
-  aligned. This greatly improves readability.
-  Alignments are achieved by the means of tabs, not spaces. Remember
-  that tabs are set to 8 in the Linux kernel code.
-
-* [Layout] Avoid extra empty lines between comments and what they
-  comment. Respect the coding style (see Documentation/CodingStyle),
-  in particular when it comes to placing curly braces.
-
-* [Comments] Make sure that no comment refers to a file that isn't
-  part of the Linux source tree (typically doc/chips/<chip name>),
-  and that remaining comments still match the code. Merging comment
-  lines when possible is encouraged.