ChangeSet 1.1496.6.2, 2003/12/04 00:43:55-08:00, khali at linux-fr.org [PATCH] I2C: i2c documentation (1 of 2) This is the document I wrote (and you reviewed) about porting client drivers to Linux 2.6. The retained name is "porting-clients" (in line with writing-clients). I won't commit it to i2c/lm_sensors2 CVS, since that document is of no use outside of the 2.6 kernel (and I'm bored keeping files in sync). Documentation/i2c/porting-clients | 121 ++++++++++++++++++++++++++++++++++++++ 1 files changed, 121 insertions(+) diff -Nru a/Documentation/i2c/porting-clients b/Documentation/i2c/porting-clients --- /dev/null Wed Dec 31 16:00:00 1969 +++ b/Documentation/i2c/porting-clients Tue Dec 30 12:32:57 2003 @@ -0,0 +1,121 @@ +Revision 3, 2003-10-04 +Jean Delvare <khali at linux-fr.org> +Greg KH <greg at kroah.com> + +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 <linux/i2c-proc.h> with + <linux/i2c-sensor.h>. Includes typically look like that: + #include <linux/module.h> + #include <linux/init.h> + #include <linux/slab.h> + #include <linux/i2c.h> + #include <linux/i2c-sensor.h> + #include <linux/i2c-vid.h> /* if you need VRM support */ + #include <asm/io.h> /* if you have I/O operations */ + Some extra headers may be required for a given driver. + +* [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 (e.g. + swap_bytes) 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, right after the static id definition + line, 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 <sensors at stimpy.netroedge.com> 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_ADAP_CLASS_SMBUS, using the + following construct: + if (!(adapter->class & I2C_ADAP_CLASS_SMBUS)) + 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"). 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. + +* [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. + +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(&adapter->dev, + "lm75_detect called for an ISA bus adapter?!?\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.
