5071860aba
Kill normal_isa in header files, documentation and all chip drivers, as it is no more used. normal_i2c could be renamed to normal, but I decided not to do so at the moment, so as to limit the number of changes. This might be done later as part of the i2c_probe/i2c_detect merge. Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
135 lines
6.0 KiB
Plaintext
135 lines
6.0 KiB
Plaintext
Revision 4, 2004-03-30
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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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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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* [Includes] Get rid of "version.h". Replace <linux/i2c-proc.h> with
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<linux/i2c-sensor.h>. 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/i2c.h>
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#include <linux/i2c-sensor.h>
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#include <linux/i2c-vid.h> /* if you need VRM support */
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#include <asm/io.h> /* if you have I/O operations */
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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.
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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 void lm75_update_client(struct i2c_client *client);
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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 (lm78 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/i2c/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/i2c/sysfs-interface file.
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* [Attach] For I2C drivers, the attach function should make sure
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that the adapter's class has I2C_CLASS_HWMON, using the
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following construct:
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if (!(adapter->class & I2C_CLASS_HWMON))
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return 0;
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ISA-only drivers of course don't need this.
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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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(typically the driver name, e.g. "lm75").
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In i2c-only drivers, drop the i2c_is_isa_adapter check, it's
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useless. Same for isa-only drivers, as the test would always be
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true. Only hybrid drivers (which are quite rare) still need it.
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The errorN labels are reduced to the number needed. If that number
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is 2 (i2c-only drivers), it is advised that the labels are named
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exit and exit_free. For i2c+isa drivers, labels should be named
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ERROR0, ERROR1 and ERROR2. 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 memset to fill the client and data area with 0x00.
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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 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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Drop client->id.
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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 is), and initialization should be
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limited to the strictly necessary steps.
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* [Detach] Get rid of data, remove the call to
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i2c_deregister_entry.
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* [Update] Don't access client->data directly, use
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i2c_get_clientdata(client) instead.
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* [Interface] Init function should not print anything. Make sure
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there is a MODULE_LICENSE() line, at the bottom of the file
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(after MODULE_AUTHOR() and MODULE_DESCRIPTION(), in this order).
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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/pr_debug for debugging purposes are replaced
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by calls to dev_dbg. Here is an example on how to call it (taken
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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, initial
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values) should be aligned. This greatly improves readability.
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Same goes for variables declarations. Alignments are achieved by the
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means of tabs, not spaces. Remember that tabs are set to 8 in the
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Linux kernel code.
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* [Structure definition] The name field should be standardized. All
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lowercase and as simple as the driver name itself (e.g. "lm75").
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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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