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SubjectRe: [PATCH] i2c driver fixes for 2.6.0
ChangeSet 1.1496.6.2, 2003/12/04 00:43:55-08:00,

[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 <>
+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 <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.
+ 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 <> 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.
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