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1 | How to Get Your Patch Accepted Into the Hwmon Subsystem |
2 | ------------------------------------------------------- | |
3 | ||
ac20ad14 | 4 | This text is a collection of suggestions for people writing patches or |
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5 | drivers for the hwmon subsystem. Following these suggestions will greatly |
6 | increase the chances of your change being accepted. | |
7 | ||
8 | ||
9 | 1. 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 | |
40b31360 | 30 | CONFIG_SMP, make sure it compiles for all configuration variants. |
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31 | |
32 | ||
33 | 2. 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 | ||
48 | 3. 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 | ||
07d33600 | 62 | * Make sure that all dependencies are listed in Kconfig. |
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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 | ||
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71 | * Use devres functions whenever possible to allocate resources. For rationale |
72 | and supported functions, please see Documentation/driver-model/devres.txt. | |
73 | ||
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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 | ||
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84 | * Only the following I2C addresses shall be probed: 0x18-0x1f, 0x28-0x2f, |
85 | 0x48-0x4f, 0x58, 0x5c, 0x73 and 0x77. Probing other addresses is strongly | |
86 | discouraged as it is known to cause trouble with other (non-hwmon) I2C | |
87 | chips. If your chip lives at an address which can't be probed then the | |
88 | device will have to be instantiated explicitly (which is always better | |
89 | anyway.) | |
90 | ||
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91 | * Avoid writing to chip registers in the detect function. If you have to write, |
92 | only do it after you have already gathered enough data to be certain that the | |
93 | detection is going to be successful. | |
94 | ||
95 | Keep in mind that the chip might not be what your driver believes it is, and | |
96 | writing to it might cause a bad misconfiguration. | |
97 | ||
98 | * Make sure there are no race conditions in the probe function. Specifically, | |
99 | completely initialize your chip first, then create sysfs entries and register | |
100 | with the hwmon subsystem. | |
101 | ||
102 | * Do not provide support for deprecated sysfs attributes. | |
103 | ||
104 | * Do not create non-standard attributes unless really needed. If you have to use | |
105 | non-standard attributes, or you believe you do, discuss it on the mailing list | |
106 | first. Either case, provide a detailed explanation why you need the | |
107 | non-standard attribute(s). | |
108 | Standard attributes are specified in Documentation/hwmon/sysfs-interface. | |
109 | ||
110 | * When deciding which sysfs attributes to support, look at the chip's | |
111 | capabilities. While we do not expect your driver to support everything the | |
112 | chip may offer, it should at least support all limits and alarms. | |
113 | ||
114 | * Last but not least, please check if a driver for your chip already exists | |
115 | before starting to write a new driver. Especially for temperature sensors, | |
116 | new chips are often variants of previously released chips. In some cases, | |
117 | a presumably new chip may simply have been relabeled. |