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/process/submit-checklist.rst
 14    Documentation/process/submitting-drivers.rst
 15    Documentation/process/submitting-patches.rst
 16    Documentation/process/coding-style.rst
 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
 382. 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
 533. 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.