Based on kernel version 4.9. Page generated on 2016-12-21 14:34 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 * 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. 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 35 CONFIG_SMP, make sure it compiles for all configuration variants. 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 67 * Make sure that all dependencies are listed in Kconfig. 68 69 * Please list include files in alphabetic order. 70 71 * Please align continuation lines with '(' on the previous line. 72 73 * Avoid forward declarations if you can. Rearrange the code if necessary. 74 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 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 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 90 * Use devres functions whenever possible to allocate resources. For rationale 91 and supported functions, please see Documentation/driver-model/devres.txt. 92 If a function is not supported by devres, consider using devm_add_action(). 93 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. 103 104 * 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.) 110 111 * 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, 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. 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.