Based on kernel version 4.7.2. Page generated on 2016-08-22 22:46 EST.
1 How to Get Your Patch Accepted Into the Hwmon Subsystem 2 ------------------------------------------------------- 3 4 This text is a collection of suggestions for people writing patches or 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 30 CONFIG_SMP, make sure it compiles for all configuration variants. 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 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 * 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 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.