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Jean Delvaref4b50262005-07-31 21:49:03 +02001Revision 5, 2005-07-29
Linus Torvalds1da177e2005-04-16 15:20:36 -07002Jean Delvare <khali@linux-fr.org>
3Greg KH <greg@kroah.com>
4
5This is a guide on how to convert I2C chip drivers from Linux 2.4 to
6Linux 2.6. I have been using existing drivers (lm75, lm78) as examples.
7Then I converted a driver myself (lm83) and updated this document.
8
9There are two sets of points below. The first set concerns technical
10changes. The second set concerns coding policy. Both are mandatory.
11
12Although reading this guide will help you porting drivers, I suggest
13you keep an eye on an already ported driver while porting your own
14driver. This will help you a lot understanding what this guide
15exactly means. Choose the chip driver that is the more similar to
16yours for best results.
17
18Technical changes:
19
Jean Delvaref4b50262005-07-31 21:49:03 +020020* [Includes] Get rid of "version.h" and <linux/i2c-proc.h>.
21 Includes typically look like that:
Linus Torvalds1da177e2005-04-16 15:20:36 -070022 #include <linux/module.h>
23 #include <linux/init.h>
24 #include <linux/slab.h>
25 #include <linux/i2c.h>
Jean Delvare303760b2005-07-31 21:52:01 +020026 #include <linux/hwmon.h> /* for hardware monitoring drivers */
27 #include <linux/hwmon-sysfs.h>
28 #include <linux/hwmon-vid.h> /* if you need VRM support */
Linus Torvalds1da177e2005-04-16 15:20:36 -070029 #include <asm/io.h> /* if you have I/O operations */
30 Please respect this inclusion order. Some extra headers may be
31 required for a given driver (e.g. "lm75.h").
32
Jean Delvare50718602005-07-20 00:02:32 +020033* [Addresses] SENSORS_I2C_END becomes I2C_CLIENT_END, ISA addresses
34 are no more handled by the i2c core.
Jean Delvaref4b50262005-07-31 21:49:03 +020035 SENSORS_INSMOD_<n> becomes I2C_CLIENT_INSMOD_<n>.
Linus Torvalds1da177e2005-04-16 15:20:36 -070036
37* [Client data] Get rid of sysctl_id. Try using standard names for
38 register values (for example, temp_os becomes temp_max). You're
39 still relatively free here, but you *have* to follow the standard
40 names for sysfs files (see the Sysctl section below).
41
42* [Function prototypes] The detect functions loses its flags
43 parameter. Sysctl (e.g. lm75_temp) and miscellaneous functions
44 are off the list of prototypes. This usually leaves five
45 prototypes:
46 static int lm75_attach_adapter(struct i2c_adapter *adapter);
47 static int lm75_detect(struct i2c_adapter *adapter, int address,
48 int kind);
49 static void lm75_init_client(struct i2c_client *client);
50 static int lm75_detach_client(struct i2c_client *client);
51 static void lm75_update_client(struct i2c_client *client);
52
53* [Sysctl] All sysctl stuff is of course gone (defines, ctl_table
54 and functions). Instead, you have to define show and set functions for
55 each sysfs file. Only define set for writable values. Take a look at an
56 existing 2.6 driver for details (lm78 for example). Don't forget
57 to define the attributes for each file (this is that step that
58 links callback functions). Use the file names specified in
59 Documentation/i2c/sysfs-interface for the individual files. Also
60 convert the units these files read and write to the specified ones.
61 If you need to add a new type of file, please discuss it on the
Jean Delvarecc0b07e2005-05-22 09:39:11 +020062 sensors mailing list <lm-sensors@lm-sensors.org> by providing a
Linus Torvalds1da177e2005-04-16 15:20:36 -070063 patch to the Documentation/i2c/sysfs-interface file.
64
65* [Attach] For I2C drivers, the attach function should make sure
66 that the adapter's class has I2C_CLASS_HWMON, using the
67 following construct:
68 if (!(adapter->class & I2C_CLASS_HWMON))
69 return 0;
70 ISA-only drivers of course don't need this.
Jean Delvare2ed2dc32005-07-31 21:42:02 +020071 Call i2c_probe() instead of i2c_detect().
Linus Torvalds1da177e2005-04-16 15:20:36 -070072
73* [Detect] As mentioned earlier, the flags parameter is gone.
74 The type_name and client_name strings are replaced by a single
75 name string, which will be filled with a lowercase, short string
76 (typically the driver name, e.g. "lm75").
77 In i2c-only drivers, drop the i2c_is_isa_adapter check, it's
Jean Delvare50718602005-07-20 00:02:32 +020078 useless. Same for isa-only drivers, as the test would always be
79 true. Only hybrid drivers (which are quite rare) still need it.
Linus Torvalds1da177e2005-04-16 15:20:36 -070080 The errorN labels are reduced to the number needed. If that number
81 is 2 (i2c-only drivers), it is advised that the labels are named
82 exit and exit_free. For i2c+isa drivers, labels should be named
83 ERROR0, ERROR1 and ERROR2. Don't forget to properly set err before
84 jumping to error labels. By the way, labels should be left-aligned.
85 Use memset to fill the client and data area with 0x00.
86 Use i2c_set_clientdata to set the client data (as opposed to
87 a direct access to client->data).
88 Use strlcpy instead of strcpy to copy the client name.
89 Replace the sysctl directory registration by calls to
90 device_create_file. Move the driver initialization before any
91 sysfs file creation.
92 Drop client->id.
Jean Delvare4c9337d2005-08-09 20:28:10 +020093 Drop any 24RF08 corruption prevention you find, as this is now done
94 at the i2c-core level, and doing it twice voids it.
Linus Torvalds1da177e2005-04-16 15:20:36 -070095
96* [Init] Limits must not be set by the driver (can be done later in
97 user-space). Chip should not be reset default (although a module
98 parameter may be used to force is), and initialization should be
99 limited to the strictly necessary steps.
100
101* [Detach] Get rid of data, remove the call to
Jean Delvare7bef5592005-07-27 22:14:49 +0200102 i2c_deregister_entry. Do not log an error message if
103 i2c_detach_client fails, as i2c-core will now do it for you.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700104
105* [Update] Don't access client->data directly, use
106 i2c_get_clientdata(client) instead.
107
108* [Interface] Init function should not print anything. Make sure
109 there is a MODULE_LICENSE() line, at the bottom of the file
110 (after MODULE_AUTHOR() and MODULE_DESCRIPTION(), in this order).
111
112Coding policy:
113
114* [Copyright] Use (C), not (c), for copyright.
115
116* [Debug/log] Get rid of #ifdef DEBUG/#endif constructs whenever you
117 can. Calls to printk/pr_debug for debugging purposes are replaced
118 by calls to dev_dbg. Here is an example on how to call it (taken
119 from lm75_detect):
120 dev_dbg(&client->dev, "Starting lm75 update\n");
121 Replace other printk calls with the dev_info, dev_err or dev_warn
122 function, as appropriate.
123
124* [Constants] Constants defines (registers, conversions, initial
125 values) should be aligned. This greatly improves readability.
126 Same goes for variables declarations. Alignments are achieved by the
127 means of tabs, not spaces. Remember that tabs are set to 8 in the
128 Linux kernel code.
129
130* [Structure definition] The name field should be standardized. All
131 lowercase and as simple as the driver name itself (e.g. "lm75").
132
133* [Layout] Avoid extra empty lines between comments and what they
134 comment. Respect the coding style (see Documentation/CodingStyle),
135 in particular when it comes to placing curly braces.
136
137* [Comments] Make sure that no comment refers to a file that isn't
138 part of the Linux source tree (typically doc/chips/<chip name>),
139 and that remaining comments still match the code. Merging comment
140 lines when possible is encouraged.