Documentation/hwmon/submitting-patches.rst

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