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1 | Revision 7, 2007-04-19 | ||
2 | Jean Delvare <khali@linux-fr.org> | ||
3 | Greg KH <greg@kroah.com> | ||
4 | |||
5 | This is a guide on how to convert I2C chip drivers from Linux 2.4 to | ||
6 | Linux 2.6. I have been using existing drivers (lm75, lm78) as examples. | ||
7 | Then I converted a driver myself (lm83) and updated this document. | ||
8 | Note that this guide is strongly oriented towards hardware monitoring | ||
9 | drivers. Many points are still valid for other type of drivers, but | ||
10 | others may be irrelevant. | ||
11 | |||
12 | There are two sets of points below. The first set concerns technical | ||
13 | changes. The second set concerns coding policy. Both are mandatory. | ||
14 | |||
15 | Although reading this guide will help you porting drivers, I suggest | ||
16 | you keep an eye on an already ported driver while porting your own | ||
17 | driver. This will help you a lot understanding what this guide | ||
18 | exactly means. Choose the chip driver that is the more similar to | ||
19 | yours for best results. | ||
20 | |||
21 | Technical 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 | |||
136 | Coding 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. | ||