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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 | ||
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18 | * Please run your patch through 'checkpatch --strict'. There should be no |
19 | errors, no warnings, and few if any check messages. If there are any | |
20 | messages, please be prepared to explain. | |
21 | ||
22 | * If your patch generates checkpatch errors, warnings, or check messages, | |
23 | please refrain from explanations such as "I prefer that coding style". | |
24 | Keep in mind that each unnecessary message helps hiding a real problem, | |
25 | and a consistent coding style makes it easier for others to understand | |
26 | and review the code. | |
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27 | |
28 | * Please test your patch thoroughly. We are not your test group. | |
29 | Sometimes a patch can not or not completely be tested because of missing | |
30 | hardware. In such cases, you should test-build the code on at least one | |
31 | architecture. If run-time testing was not achieved, it should be written | |
32 | explicitly below the patch header. | |
33 | ||
34 | * If your patch (or the driver) is affected by configuration options such as | |
40b31360 | 35 | CONFIG_SMP, make sure it compiles for all configuration variants. |
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36 | |
37 | ||
38 | 2. Adding functionality to existing drivers | |
39 | ------------------------------------------- | |
40 | ||
41 | * Make sure the documentation in Documentation/hwmon/<driver_name> is up to | |
42 | date. | |
43 | ||
44 | * Make sure the information in Kconfig is up to date. | |
45 | ||
46 | * If the added functionality requires some cleanup or structural changes, split | |
47 | your patch into a cleanup part and the actual addition. This makes it easier | |
48 | to review your changes, and to bisect any resulting problems. | |
49 | ||
50 | * Never mix bug fixes, cleanup, and functional enhancements in a single patch. | |
51 | ||
52 | ||
53 | 3. New drivers | |
54 | -------------- | |
55 | ||
56 | * Running your patch or driver file(s) through checkpatch does not mean its | |
57 | formatting is clean. If unsure about formatting in your new driver, run it | |
58 | through Lindent. Lindent is not perfect, and you may have to do some minor | |
59 | cleanup, but it is a good start. | |
60 | ||
61 | * Consider adding yourself to MAINTAINERS. | |
62 | ||
63 | * Document the driver in Documentation/hwmon/<driver_name>. | |
64 | ||
65 | * Add the driver to Kconfig and Makefile in alphabetical order. | |
66 | ||
07d33600 | 67 | * Make sure that all dependencies are listed in Kconfig. |
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69 | * Please list include files in alphabetic order. |
70 | ||
71 | * Please align continuation lines with '(' on the previous line. | |
72 | ||
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73 | * Avoid forward declarations if you can. Rearrange the code if necessary. |
74 | ||
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75 | * Avoid macros to generate groups of sensor attributes. It not only confuses |
76 | checkpatch, but also makes it more difficult to review the code. | |
77 | ||
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78 | * Avoid calculations in macros and macro-generated functions. While such macros |
79 | may save a line or so in the source, it obfuscates the code and makes code | |
80 | review more difficult. It may also result in code which is more complicated | |
81 | than necessary. Use inline functions or just regular functions instead. | |
82 | ||
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83 | * Limit the number of kernel log messages. In general, your driver should not |
84 | generate an error message just because a runtime operation failed. Report | |
85 | errors to user space instead, using an appropriate error code. Keep in mind | |
86 | that kernel error log messages not only fill up the kernel log, but also are | |
87 | printed synchronously, most likely with interrupt disabled, often to a serial | |
88 | console. Excessive logging can seriously affect system performance. | |
89 | ||
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90 | * Use devres functions whenever possible to allocate resources. For rationale |
91 | and supported functions, please see Documentation/driver-model/devres.txt. | |
165720d9 | 92 | If a function is not supported by devres, consider using devm_add_action(). |
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94 | * If the driver has a detect function, make sure it is silent. Debug messages |
95 | and messages printed after a successful detection are acceptable, but it | |
96 | must not print messages such as "Chip XXX not found/supported". | |
97 | ||
98 | Keep in mind that the detect function will run for all drivers supporting an | |
99 | address if a chip is detected on that address. Unnecessary messages will just | |
100 | pollute the kernel log and not provide any value. | |
101 | ||
102 | * Provide a detect function if and only if a chip can be detected reliably. | |
103 | ||
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104 | * Only the following I2C addresses shall be probed: 0x18-0x1f, 0x28-0x2f, |
105 | 0x48-0x4f, 0x58, 0x5c, 0x73 and 0x77. Probing other addresses is strongly | |
106 | discouraged as it is known to cause trouble with other (non-hwmon) I2C | |
107 | chips. If your chip lives at an address which can't be probed then the | |
108 | device will have to be instantiated explicitly (which is always better | |
109 | anyway.) | |
110 | ||
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111 | * Avoid writing to chip registers in the detect function. If you have to write, |
112 | only do it after you have already gathered enough data to be certain that the | |
113 | detection is going to be successful. | |
114 | ||
115 | Keep in mind that the chip might not be what your driver believes it is, and | |
116 | writing to it might cause a bad misconfiguration. | |
117 | ||
118 | * Make sure there are no race conditions in the probe function. Specifically, | |
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119 | completely initialize your chip and your driver first, then register with |
120 | the hwmon subsystem. | |
121 | ||
122 | * Use devm_hwmon_device_register_with_groups() or, if your driver needs a remove | |
123 | function, hwmon_device_register_with_groups() to register your driver with the | |
124 | hwmon subsystem. Try using devm_add_action() instead of a remove function if | |
125 | possible. Do not use hwmon_device_register(). | |
126 | ||
127 | * Your driver should be buildable as module. If not, please be prepared to | |
128 | explain why it has to be built into the kernel. | |
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129 | |
130 | * Do not provide support for deprecated sysfs attributes. | |
131 | ||
132 | * Do not create non-standard attributes unless really needed. If you have to use | |
133 | non-standard attributes, or you believe you do, discuss it on the mailing list | |
134 | first. Either case, provide a detailed explanation why you need the | |
135 | non-standard attribute(s). | |
136 | Standard attributes are specified in Documentation/hwmon/sysfs-interface. | |
137 | ||
138 | * When deciding which sysfs attributes to support, look at the chip's | |
139 | capabilities. While we do not expect your driver to support everything the | |
140 | chip may offer, it should at least support all limits and alarms. | |
141 | ||
142 | * Last but not least, please check if a driver for your chip already exists | |
143 | before starting to write a new driver. Especially for temperature sensors, | |
144 | new chips are often variants of previously released chips. In some cases, | |
145 | a presumably new chip may simply have been relabeled. |