Revision 4, 2004-03-30 Jean Delvare Greg KH This is a guide on how to convert I2C chip drivers from Linux 2.4 to Linux 2.6. I have been using existing drivers (lm75, lm78) as examples. Then I converted a driver myself (lm83) and updated this document. There are two sets of points below. The first set concerns technical changes. The second set concerns coding policy. Both are mandatory. Although reading this guide will help you porting drivers, I suggest you keep an eye on an already ported driver while porting your own driver. This will help you a lot understanding what this guide exactly means. Choose the chip driver that is the more similar to yours for best results. Technical changes: * [Includes] Get rid of "version.h". Replace with . Includes typically look like that: #include #include #include #include #include #include /* if you need VRM support */ #include /* if you have I/O operations */ Please respect this inclusion order. Some extra headers may be required for a given driver (e.g. "lm75.h"). * [Addresses] SENSORS_I2C_END becomes I2C_CLIENT_END, SENSORS_ISA_END becomes I2C_CLIENT_ISA_END. * [Client data] Get rid of sysctl_id. Try using standard names for register values (for example, temp_os becomes temp_max). You're still relatively free here, but you *have* to follow the standard names for sysfs files (see the Sysctl section below). * [Function prototypes] The detect functions loses its flags parameter. Sysctl (e.g. lm75_temp) and miscellaneous functions are off the list of prototypes. This usually leaves five prototypes: static int lm75_attach_adapter(struct i2c_adapter *adapter); static int lm75_detect(struct i2c_adapter *adapter, int address, int kind); static void lm75_init_client(struct i2c_client *client); static int lm75_detach_client(struct i2c_client *client); static void lm75_update_client(struct i2c_client *client); * [Sysctl] All sysctl stuff is of course gone (defines, ctl_table and functions). Instead, you have to define show and set functions for each sysfs file. Only define set for writable values. Take a look at an existing 2.6 driver for details (lm78 for example). Don't forget to define the attributes for each file (this is that step that links callback functions). Use the file names specified in Documentation/i2c/sysfs-interface for the individual files. Also convert the units these files read and write to the specified ones. If you need to add a new type of file, please discuss it on the sensors mailing list by providing a patch to the Documentation/i2c/sysfs-interface file. * [Attach] For I2C drivers, the attach function should make sure that the adapter's class has I2C_CLASS_HWMON, using the following construct: if (!(adapter->class & I2C_CLASS_HWMON)) return 0; ISA-only drivers of course don't need this. * [Detect] As mentioned earlier, the flags parameter is gone. The type_name and client_name strings are replaced by a single name string, which will be filled with a lowercase, short string (typically the driver name, e.g. "lm75"). In i2c-only drivers, drop the i2c_is_isa_adapter check, it's useless. The errorN labels are reduced to the number needed. If that number is 2 (i2c-only drivers), it is advised that the labels are named exit and exit_free. For i2c+isa drivers, labels should be named ERROR0, ERROR1 and ERROR2. Don't forget to properly set err before jumping to error labels. By the way, labels should be left-aligned. Use memset to fill the client and data area with 0x00. Use i2c_set_clientdata to set the client data (as opposed to a direct access to client->data). Use strlcpy instead of strcpy to copy the client name. Replace the sysctl directory registration by calls to device_create_file. Move the driver initialization before any sysfs file creation. Drop client->id. * [Init] Limits must not be set by the driver (can be done later in user-space). Chip should not be reset default (although a module parameter may be used to force is), and initialization should be limited to the strictly necessary steps. * [Detach] Get rid of data, remove the call to i2c_deregister_entry. * [Update] Don't access client->data directly, use i2c_get_clientdata(client) instead. * [Interface] Init function should not print anything. Make sure there is a MODULE_LICENSE() line, at the bottom of the file (after MODULE_AUTHOR() and MODULE_DESCRIPTION(), in this order). Coding policy: * [Copyright] Use (C), not (c), for copyright. * [Debug/log] Get rid of #ifdef DEBUG/#endif constructs whenever you can. Calls to printk/pr_debug for debugging purposes are replaced by calls to dev_dbg. Here is an example on how to call it (taken from lm75_detect): dev_dbg(&client->dev, "Starting lm75 update\n"); Replace other printk calls with the dev_info, dev_err or dev_warn function, as appropriate. * [Constants] Constants defines (registers, conversions, initial values) should be aligned. This greatly improves readability. Same goes for variables declarations. Alignments are achieved by the means of tabs, not spaces. Remember that tabs are set to 8 in the Linux kernel code. * [Structure definition] The name field should be standardized. All lowercase and as simple as the driver name itself (e.g. "lm75"). * [Layout] Avoid extra empty lines between comments and what they comment. Respect the coding style (see Documentation/CodingStyle), in particular when it comes to placing curly braces. * [Comments] Make sure that no comment refers to a file that isn't part of the Linux source tree (typically doc/chips/), and that remaining comments still match the code. Merging comment lines when possible is encouraged.