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1Revision 7, 2007-04-19
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* [Driver type] Any driver that was relying on i2c-isa has to be
24 converted to a proper isa, platform or pci driver. This is not
25 covered by this guide.
26
27* [Includes] Get rid of "version.h" and <linux/i2c-proc.h>.
28 Includes typically look like that:
29 #include <linux/module.h>
30 #include <linux/init.h>
31 #include <linux/slab.h>
32 #include <linux/jiffies.h>
33 #include <linux/i2c.h>
34 #include <linux/hwmon.h> /* for hardware monitoring drivers */
35 #include <linux/hwmon-sysfs.h>
36 #include <linux/hwmon-vid.h> /* if you need VRM support */
37 #include <linux/err.h> /* for class registration */
38 Please respect this inclusion order. Some extra headers may be
39 required for a given driver (e.g. "lm75.h").
40
41* [Addresses] SENSORS_I2C_END becomes I2C_CLIENT_END, ISA addresses
42 are no more handled by the i2c core. Address ranges are no more
43 supported either, define each individual address separately.
44 SENSORS_INSMOD_<n> becomes I2C_CLIENT_INSMOD_<n>.
45
46* [Client data] Get rid of sysctl_id. Try using standard names for
47 register values (for example, temp_os becomes temp_max). You're
48 still relatively free here, but you *have* to follow the standard
49 names for sysfs files (see the Sysctl section below).
50
51* [Function prototypes] The detect functions loses its flags
52 parameter. Sysctl (e.g. lm75_temp) and miscellaneous functions
53 are off the list of prototypes. This usually leaves five
54 prototypes:
55 static int lm75_attach_adapter(struct i2c_adapter *adapter);
56 static int lm75_detect(struct i2c_adapter *adapter, int address,
57 int kind);
58 static void lm75_init_client(struct i2c_client *client);
59 static int lm75_detach_client(struct i2c_client *client);
60 static struct lm75_data lm75_update_device(struct device *dev);
61
62* [Sysctl] All sysctl stuff is of course gone (defines, ctl_table
63 and functions). Instead, you have to define show and set functions for
64 each sysfs file. Only define set for writable values. Take a look at an
65 existing 2.6 driver for details (it87 for example). Don't forget
66 to define the attributes for each file (this is that step that
67 links callback functions). Use the file names specified in
68 Documentation/hwmon/sysfs-interface for the individual files. Also
69 convert the units these files read and write to the specified ones.
70 If you need to add a new type of file, please discuss it on the
71 sensors mailing list <lm-sensors@lm-sensors.org> by providing a
72 patch to the Documentation/hwmon/sysfs-interface file.
73
74* [Attach] The attach function should make sure that the adapter's
75 class has I2C_CLASS_HWMON (or whatever class is suitable for your
76 driver), using the following construct:
77 if (!(adapter->class & I2C_CLASS_HWMON))
78 return 0;
79 Call i2c_probe() instead of i2c_detect().
80
81* [Detect] As mentioned earlier, the flags parameter is gone.
82 The type_name and client_name strings are replaced by a single
83 name string, which will be filled with a lowercase, short string.
84 The labels used for error paths are reduced to the number needed.
85 It is advised that the labels are given descriptive names such as
86 exit and exit_free. Don't forget to properly set err before
87 jumping to error labels. By the way, labels should be left-aligned.
88 Use kzalloc instead of kmalloc.
89 Use i2c_set_clientdata to set the client data (as opposed to
90 a direct access to client->data).
91 Use strlcpy instead of strcpy or snprintf to copy the client name.
92 Replace the sysctl directory registration by calls to
93 device_create_file. Move the driver initialization before any
94 sysfs file creation.
95 Register the client with the hwmon class (using hwmon_device_register)
96 if applicable.
97 Drop client->id.
98 Drop any 24RF08 corruption prevention you find, as this is now done
99 at the i2c-core level, and doing it twice voids it.
100 Don't add I2C_CLIENT_ALLOW_USE to client->flags, it's the default now.
101
102* [Init] Limits must not be set by the driver (can be done later in
103 user-space). Chip should not be reset default (although a module
104 parameter may be used to force it), and initialization should be
105 limited to the strictly necessary steps.
106
107* [Detach] Remove the call to i2c_deregister_entry. Do not log an
108 error message if i2c_detach_client fails, as i2c-core will now do
109 it for you.
110 Unregister from the hwmon class if applicable.
111
112* [Update] The function prototype changed, it is now
113 passed a device structure, which you have to convert to a client
114 using to_i2c_client(dev). The update function should return a
115 pointer to the client data.
116 Don't access client->data directly, use i2c_get_clientdata(client)
117 instead.
118 Use time_after() instead of direct jiffies comparison.
119
120* [Interface] Make sure there is a MODULE_LICENSE() line, at the bottom
121 of the file (after MODULE_AUTHOR() and MODULE_DESCRIPTION(), in this
122 order).
123
124* [Driver] The flags field of the i2c_driver structure is gone.
125 I2C_DF_NOTIFY is now the default behavior.
126 The i2c_driver structure has a driver member, which is itself a
127 structure, those name member should be initialized to a driver name
128 string. i2c_driver itself has no name member anymore.
129
130* [Driver model] Instead of shutdown or reboot notifiers, provide a
131 shutdown() method in your driver.
132
133* [Power management] Use the driver model suspend() and resume()
134 callbacks instead of the obsolete pm_register() calls.
135
136Coding policy:
137
138* [Copyright] Use (C), not (c), for copyright.
139
140* [Debug/log] Get rid of #ifdef DEBUG/#endif constructs whenever you
141 can. Calls to printk for debugging purposes are replaced by calls to
142 dev_dbg where possible, else to pr_debug. Here is an example of how
143 to call it (taken from lm75_detect):
144 dev_dbg(&client->dev, "Starting lm75 update\n");
145 Replace other printk calls with the dev_info, dev_err or dev_warn
146 function, as appropriate.
147
148* [Constants] Constants defines (registers, conversions) should be
149 aligned. This greatly improves readability.
150 Alignments are achieved by the means of tabs, not spaces. Remember
151 that tabs are set to 8 in the Linux kernel code.
152
153* [Layout] Avoid extra empty lines between comments and what they
154 comment. Respect the coding style (see Documentation/CodingStyle),
155 in particular when it comes to placing curly braces.
156
157* [Comments] Make sure that no comment refers to a file that isn't
158 part of the Linux source tree (typically doc/chips/<chip name>),
159 and that remaining comments still match the code. Merging comment
160 lines when possible is encouraged.
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