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1Revision 6, 2005-11-20
2Jean 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.
8Note that this guide is strongly oriented towards hardware monitoring
9drivers. Many points are still valid for other type of drivers, but
10others may be irrelevant.
11
12There are two sets of points below. The first set concerns technical
13changes. The second set concerns coding policy. Both are mandatory.
14
15Although reading this guide will help you porting drivers, I suggest
16you keep an eye on an already ported driver while porting your own
17driver. This will help you a lot understanding what this guide
18exactly means. Choose the chip driver that is the more similar to
19yours for best results.
20
21Technical changes:
22
23* [Includes] Get rid of "version.h" and <linux/i2c-proc.h>.
24 Includes typically look like that:
25 #include <linux/module.h>
26 #include <linux/init.h>
27 #include <linux/slab.h>
28 #include <linux/jiffies.h>
29 #include <linux/i2c.h>
30 #include <linux/i2c-isa.h> /* for ISA drivers */
31 #include <linux/hwmon.h> /* for hardware monitoring drivers */
32 #include <linux/hwmon-sysfs.h>
33 #include <linux/hwmon-vid.h> /* if you need VRM support */
34 #include <linux/err.h> /* for class registration */
35 #include <asm/io.h> /* if you have I/O operations */
36 Please respect this inclusion order. Some extra headers may be
37 required for a given driver (e.g. "lm75.h").
38
39* [Addresses] SENSORS_I2C_END becomes I2C_CLIENT_END, ISA addresses
40 are no more handled by the i2c core. Address ranges are no more
41 supported either, define each individual address separately.
42 SENSORS_INSMOD_<n> becomes I2C_CLIENT_INSMOD_<n>.
43
44* [Client data] Get rid of sysctl_id. Try using standard names for
45 register values (for example, temp_os becomes temp_max). You're
46 still relatively free here, but you *have* to follow the standard
47 names for sysfs files (see the Sysctl section below).
48
49* [Function prototypes] The detect functions loses its flags
50 parameter. Sysctl (e.g. lm75_temp) and miscellaneous functions
51 are off the list of prototypes. This usually leaves five
52 prototypes:
53 static int lm75_attach_adapter(struct i2c_adapter *adapter);
54 static int lm75_detect(struct i2c_adapter *adapter, int address,
55 int kind);
56 static void lm75_init_client(struct i2c_client *client);
57 static int lm75_detach_client(struct i2c_client *client);
58 static struct lm75_data lm75_update_device(struct device *dev);
59
60* [Sysctl] All sysctl stuff is of course gone (defines, ctl_table
61 and functions). Instead, you have to define show and set functions for
62 each sysfs file. Only define set for writable values. Take a look at an
63 existing 2.6 driver for details (it87 for example). Don't forget
64 to define the attributes for each file (this is that step that
65 links callback functions). Use the file names specified in
66 Documentation/hwmon/sysfs-interface for the individual files. Also
67 convert the units these files read and write to the specified ones.
68 If you need to add a new type of file, please discuss it on the
69 sensors mailing list <lm-sensors@lm-sensors.org> by providing a
70 patch to the Documentation/hwmon/sysfs-interface file.
71
72* [Attach] For I2C drivers, the attach function should make sure
73 that the adapter's class has I2C_CLASS_HWMON (or whatever class is
74 suitable for your driver), using the following construct:
75 if (!(adapter->class & I2C_CLASS_HWMON))
76 return 0;
77 ISA-only drivers of course don't need this.
78 Call i2c_probe() instead of i2c_detect().
79
80* [Detect] As mentioned earlier, the flags parameter is gone.
81 The type_name and client_name strings are replaced by a single
82 name string, which will be filled with a lowercase, short string.
83 In i2c-only drivers, drop the i2c_is_isa_adapter check, it's
84 useless. Same for isa-only drivers, as the test would always be
85 true. Only hybrid drivers (which are quite rare) still need it.
86 The labels used for error paths are reduced to the number needed.
87 It is advised that the labels are given descriptive names such as
88 exit and exit_free. Don't forget to properly set err before
89 jumping to error labels. By the way, labels should be left-aligned.
90 Use kzalloc instead of kmalloc.
91 Use i2c_set_clientdata to set the client data (as opposed to
92 a direct access to client->data).
93 Use strlcpy instead of strcpy or snprintf to copy the client name.
94 Replace the sysctl directory registration by calls to
95 device_create_file. Move the driver initialization before any
96 sysfs file creation.
97 Register the client with the hwmon class (using hwmon_device_register)
98 if applicable.
99 Drop client->id.
100 Drop any 24RF08 corruption prevention you find, as this is now done
101 at the i2c-core level, and doing it twice voids it.
102 Don't add I2C_CLIENT_ALLOW_USE to client->flags, it's the default now.
103
104* [Init] Limits must not be set by the driver (can be done later in
105 user-space). Chip should not be reset default (although a module
106 parameter may be used to force it), and initialization should be
107 limited to the strictly necessary steps.
108
109* [Detach] Remove the call to i2c_deregister_entry. Do not log an
110 error message if i2c_detach_client fails, as i2c-core will now do
111 it for you.
112 Unregister from the hwmon class if applicable.
113
114* [Update] The function prototype changed, it is now
115 passed a device structure, which you have to convert to a client
116 using to_i2c_client(dev). The update function should return a
117 pointer to the client data.
118 Don't access client->data directly, use i2c_get_clientdata(client)
119 instead.
120 Use time_after() instead of direct jiffies comparison.
121
122* [Interface] Make sure there is a MODULE_LICENSE() line, at the bottom
123 of the file (after MODULE_AUTHOR() and MODULE_DESCRIPTION(), in this
124 order).
125
126* [Driver] The flags field of the i2c_driver structure is gone.
127 I2C_DF_NOTIFY is now the default behavior.
128 The i2c_driver structure has a driver member, which is itself a
129 structure, those name member should be initialized to a driver name
130 string. i2c_driver itself has no name member anymore.
131
132Coding policy:
133
134* [Copyright] Use (C), not (c), for copyright.
135
136* [Debug/log] Get rid of #ifdef DEBUG/#endif constructs whenever you
137 can. Calls to printk for debugging purposes are replaced by calls to
138 dev_dbg where possible, else to pr_debug. Here is an example of how
139 to call it (taken from lm75_detect):
140 dev_dbg(&client->dev, "Starting lm75 update\n");
141 Replace other printk calls with the dev_info, dev_err or dev_warn
142 function, as appropriate.
143
144* [Constants] Constants defines (registers, conversions) should be
145 aligned. This greatly improves readability.
146 Alignments are achieved by the means of tabs, not spaces. Remember
147 that tabs are set to 8 in the Linux kernel code.
148
149* [Layout] Avoid extra empty lines between comments and what they
150 comment. Respect the coding style (see Documentation/CodingStyle),
151 in particular when it comes to placing curly braces.
152
153* [Comments] Make sure that no comment refers to a file that isn't
154 part of the Linux source tree (typically doc/chips/<chip name>),
155 and that remaining comments still match the code. Merging comment
156 lines when possible is encouraged.