i2c: Delete outdated client porting guide
The document describing how to port i2c chip drivers from Linux 2.4 to Linux 2.6 is outdated.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>
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Jean Delvare
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Revision 7, 2007-04-19
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Jean Delvare <khali@linux-fr.org>
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Greg KH <greg@kroah.com>
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This is a guide on how to convert I2C chip drivers from Linux 2.4 to
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Linux 2.6. I have been using existing drivers (lm75, lm78) as examples.
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Then I converted a driver myself (lm83) and updated this document.
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Note that this guide is strongly oriented towards hardware monitoring
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drivers. Many points are still valid for other type of drivers, but
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others may be irrelevant.
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There are two sets of points below. The first set concerns technical
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changes. The second set concerns coding policy. Both are mandatory.
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Although reading this guide will help you porting drivers, I suggest
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you keep an eye on an already ported driver while porting your own
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driver. This will help you a lot understanding what this guide
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exactly means. Choose the chip driver that is the more similar to
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yours for best results.
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Technical changes:
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* [Driver type] Any driver that was relying on i2c-isa has to be
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converted to a proper isa, platform or pci driver. This is not
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covered by this guide.
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* [Includes] Get rid of "version.h" and <linux/i2c-proc.h>.
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Includes typically look like that:
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/slab.h>
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#include <linux/jiffies.h>
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#include <linux/i2c.h>
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#include <linux/hwmon.h> /* for hardware monitoring drivers */
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#include <linux/hwmon-sysfs.h>
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#include <linux/hwmon-vid.h> /* if you need VRM support */
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#include <linux/err.h> /* for class registration */
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Please respect this inclusion order. Some extra headers may be
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required for a given driver (e.g. "lm75.h").
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* [Addresses] SENSORS_I2C_END becomes I2C_CLIENT_END, ISA addresses
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are no more handled by the i2c core. Address ranges are no more
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supported either, define each individual address separately.
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SENSORS_INSMOD_<n> becomes I2C_CLIENT_INSMOD_<n>.
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* [Client data] Get rid of sysctl_id. Try using standard names for
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register values (for example, temp_os becomes temp_max). You're
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still relatively free here, but you *have* to follow the standard
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names for sysfs files (see the Sysctl section below).
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* [Function prototypes] The detect functions loses its flags
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parameter. Sysctl (e.g. lm75_temp) and miscellaneous functions
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are off the list of prototypes. This usually leaves five
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prototypes:
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static int lm75_attach_adapter(struct i2c_adapter *adapter);
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static int lm75_detect(struct i2c_adapter *adapter, int address,
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int kind);
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static void lm75_init_client(struct i2c_client *client);
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static int lm75_detach_client(struct i2c_client *client);
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static struct lm75_data lm75_update_device(struct device *dev);
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* [Sysctl] All sysctl stuff is of course gone (defines, ctl_table
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and functions). Instead, you have to define show and set functions for
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each sysfs file. Only define set for writable values. Take a look at an
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existing 2.6 driver for details (it87 for example). Don't forget
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to define the attributes for each file (this is that step that
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links callback functions). Use the file names specified in
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Documentation/hwmon/sysfs-interface for the individual files. Also
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convert the units these files read and write to the specified ones.
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If you need to add a new type of file, please discuss it on the
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sensors mailing list <lm-sensors@lm-sensors.org> by providing a
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patch to the Documentation/hwmon/sysfs-interface file.
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* [Attach] The attach function should make sure that the adapter's
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class has I2C_CLASS_HWMON (or whatever class is suitable for your
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driver), using the following construct:
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if (!(adapter->class & I2C_CLASS_HWMON))
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return 0;
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Call i2c_probe() instead of i2c_detect().
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* [Detect] As mentioned earlier, the flags parameter is gone.
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The type_name and client_name strings are replaced by a single
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name string, which will be filled with a lowercase, short string.
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The labels used for error paths are reduced to the number needed.
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It is advised that the labels are given descriptive names such as
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exit and exit_free. Don't forget to properly set err before
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jumping to error labels. By the way, labels should be left-aligned.
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Use kzalloc instead of kmalloc.
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Use i2c_set_clientdata to set the client data (as opposed to
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a direct access to client->data).
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Use strlcpy instead of strcpy or snprintf to copy the client name.
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Replace the sysctl directory registration by calls to
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device_create_file. Move the driver initialization before any
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sysfs file creation.
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Register the client with the hwmon class (using hwmon_device_register)
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if applicable.
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Drop client->id.
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Drop any 24RF08 corruption prevention you find, as this is now done
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at the i2c-core level, and doing it twice voids it.
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Don't add I2C_CLIENT_ALLOW_USE to client->flags, it's the default now.
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* [Init] Limits must not be set by the driver (can be done later in
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user-space). Chip should not be reset default (although a module
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parameter may be used to force it), and initialization should be
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limited to the strictly necessary steps.
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* [Detach] Remove the call to i2c_deregister_entry. Do not log an
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error message if i2c_detach_client fails, as i2c-core will now do
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it for you.
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Unregister from the hwmon class if applicable.
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* [Update] The function prototype changed, it is now
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passed a device structure, which you have to convert to a client
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using to_i2c_client(dev). The update function should return a
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pointer to the client data.
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Don't access client->data directly, use i2c_get_clientdata(client)
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instead.
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Use time_after() instead of direct jiffies comparison.
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* [Interface] Make sure there is a MODULE_LICENSE() line, at the bottom
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of the file (after MODULE_AUTHOR() and MODULE_DESCRIPTION(), in this
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order).
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* [Driver] The flags field of the i2c_driver structure is gone.
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I2C_DF_NOTIFY is now the default behavior.
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The i2c_driver structure has a driver member, which is itself a
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structure, those name member should be initialized to a driver name
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string. i2c_driver itself has no name member anymore.
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* [Driver model] Instead of shutdown or reboot notifiers, provide a
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shutdown() method in your driver.
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* [Power management] Use the driver model suspend() and resume()
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callbacks instead of the obsolete pm_register() calls.
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Coding policy:
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* [Copyright] Use (C), not (c), for copyright.
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* [Debug/log] Get rid of #ifdef DEBUG/#endif constructs whenever you
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can. Calls to printk for debugging purposes are replaced by calls to
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dev_dbg where possible, else to pr_debug. Here is an example of how
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to call it (taken from lm75_detect):
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dev_dbg(&client->dev, "Starting lm75 update\n");
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Replace other printk calls with the dev_info, dev_err or dev_warn
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function, as appropriate.
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* [Constants] Constants defines (registers, conversions) should be
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aligned. This greatly improves readability.
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Alignments are achieved by the means of tabs, not spaces. Remember
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that tabs are set to 8 in the Linux kernel code.
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* [Layout] Avoid extra empty lines between comments and what they
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comment. Respect the coding style (see Documentation/CodingStyle),
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in particular when it comes to placing curly braces.
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* [Comments] Make sure that no comment refers to a file that isn't
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part of the Linux source tree (typically doc/chips/<chip name>),
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and that remaining comments still match the code. Merging comment
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lines when possible is encouraged.
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