1	How to Get Your Patch Accepted Into the Hwmon Subsystem
2	-------------------------------------------------------
3
4This text is a collection of suggestions for people writing patches or
5drivers for the hwmon subsystem. Following these suggestions will greatly
6increase the chances of your change being accepted.
7
8
91. General
10----------
11
12* It should be unnecessary to mention, but please read and follow
13    Documentation/SubmitChecklist
14    Documentation/SubmittingDrivers
15    Documentation/SubmittingPatches
16    Documentation/CodingStyle
17
18* If your patch generates checkpatch warnings, please refrain from explanations
19  such as "I don't like that coding style". Keep in mind that each unnecessary
20  warning helps hiding a real problem. If you don't like the kernel coding
21  style, don't write kernel drivers.
22
23* Please test your patch thoroughly. We are not your test group.
24  Sometimes a patch can not or not completely be tested because of missing
25  hardware. In such cases, you should test-build the code on at least one
26  architecture. If run-time testing was not achieved, it should be written
27  explicitly below the patch header.
28
29* If your patch (or the driver) is affected by configuration options such as
30  CONFIG_SMP, make sure it compiles for all configuration variants.
31
32
332. Adding functionality to existing drivers
34-------------------------------------------
35
36* Make sure the documentation in Documentation/hwmon/<driver_name> is up to
37  date.
38
39* Make sure the information in Kconfig is up to date.
40
41* If the added functionality requires some cleanup or structural changes, split
42  your patch into a cleanup part and the actual addition. This makes it easier
43  to review your changes, and to bisect any resulting problems.
44
45* Never mix bug fixes, cleanup, and functional enhancements in a single patch.
46
47
483. New drivers
49--------------
50
51* Running your patch or driver file(s) through checkpatch does not mean its
52  formatting is clean. If unsure about formatting in your new driver, run it
53  through Lindent. Lindent is not perfect, and you may have to do some minor
54  cleanup, but it is a good start.
55
56* Consider adding yourself to MAINTAINERS.
57
58* Document the driver in Documentation/hwmon/<driver_name>.
59
60* Add the driver to Kconfig and Makefile in alphabetical order.
61
62* Make sure that all dependencies are listed in Kconfig.
63
64* Avoid forward declarations if you can. Rearrange the code if necessary.
65
66* Avoid calculations in macros and macro-generated functions. While such macros
67  may save a line or so in the source, it obfuscates the code and makes code
68  review more difficult. It may also result in code which is more complicated
69  than necessary. Use inline functions or just regular functions instead.
70
71* Use devres functions whenever possible to allocate resources. For rationale
72  and supported functions, please see Documentation/driver-model/devres.txt.
73
74* If the driver has a detect function, make sure it is silent. Debug messages
75  and messages printed after a successful detection are acceptable, but it
76  must not print messages such as "Chip XXX not found/supported".
77
78  Keep in mind that the detect function will run for all drivers supporting an
79  address if a chip is detected on that address. Unnecessary messages will just
80  pollute the kernel log and not provide any value.
81
82* Provide a detect function if and only if a chip can be detected reliably.
83
84* Avoid writing to chip registers in the detect function. If you have to write,
85  only do it after you have already gathered enough data to be certain that the
86  detection is going to be successful.
87
88  Keep in mind that the chip might not be what your driver believes it is, and
89  writing to it might cause a bad misconfiguration.
90
91* Make sure there are no race conditions in the probe function. Specifically,
92  completely initialize your chip first, then create sysfs entries and register
93  with the hwmon subsystem.
94
95* Do not provide support for deprecated sysfs attributes.
96
97* Do not create non-standard attributes unless really needed. If you have to use
98  non-standard attributes, or you believe you do, discuss it on the mailing list
99  first. Either case, provide a detailed explanation why you need the
100  non-standard attribute(s).
101  Standard attributes are specified in Documentation/hwmon/sysfs-interface.
102
103* When deciding which sysfs attributes to support, look at the chip's
104  capabilities. While we do not expect your driver to support everything the
105  chip may offer, it should at least support all limits and alarms.
106
107* Last but not least, please check if a driver for your chip already exists
108  before starting to write a new driver. Especially for temperature sensors,
109  new chips are often variants of previously released chips. In some cases,
110  a presumably new chip may simply have been relabeled.
111