Based on kernel version 2.6.26. Page generated on 2008-07-16 21:12 EST.
1 Revision 7, 2007-04-19 2 Jean Delvare <khali[AT]linux-fr[DOT]org> 3 Greg KH <greg[AT]kroah[DOT]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[AT]lm-sensors[DOT]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.