hwmon: Add submitting-patches checklist to documentation

When writing hardware monitoring drivers, there are some common pitfalls which
keep coming up in code reviews. This patch provides a document describing all
those pitfalls and how to avoid them.

Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Acked-by: Jean Delvare <khali@linux-fr.org>

1 files changed, 109 insertions, 0 deletions

diff --git a/Documentation/hwmon/submitting-patches b/Documentation/hwmon/submitting-patches
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index 0000000..86f42e8
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+	How to Get Your Patch Accepted Into the Hwmon Subsystem
+	-------------------------------------------------------
+
+This text is is a collection of suggestions for people writing patches or
+drivers for the hwmon subsystem. Following these suggestions will greatly
+increase the chances of your change being accepted.
+
+
+1. General
+----------
+
+* It should be unnecessary to mention, but please read and follow
+    Documentation/SubmitChecklist
+    Documentation/SubmittingDrivers
+    Documentation/SubmittingPatches
+    Documentation/CodingStyle
+
+* If your patch generates checkpatch warnings, please refrain from explanations
+  such as "I don't like that coding style". Keep in mind that each unnecessary
+  warning helps hiding a real problem. If you don't like the kernel coding
+  style, don't write kernel drivers.
+
+* Please test your patch thoroughly. We are not your test group.
+  Sometimes a patch can not or not completely be tested because of missing
+  hardware. In such cases, you should test-build the code on at least one
+  architecture. If run-time testing was not achieved, it should be written
+  explicitly below the patch header.
+
+* If your patch (or the driver) is affected by configuration options such as
+  CONFIG_SMP or CONFIG_HOTPLUG, make sure it compiles for all configuration
+  variants.
+
+
+2. Adding functionality to existing drivers
+-------------------------------------------
+
+* Make sure the documentation in Documentation/hwmon/<driver_name> is up to
+  date.
+
+* Make sure the information in Kconfig is up to date.
+
+* If the added functionality requires some cleanup or structural changes, split
+  your patch into a cleanup part and the actual addition. This makes it easier
+  to review your changes, and to bisect any resulting problems.
+
+* Never mix bug fixes, cleanup, and functional enhancements in a single patch.
+
+
+3. New drivers
+--------------
+
+* Running your patch or driver file(s) through checkpatch does not mean its
+  formatting is clean. If unsure about formatting in your new driver, run it
+  through Lindent. Lindent is not perfect, and you may have to do some minor
+  cleanup, but it is a good start.
+
+* Consider adding yourself to MAINTAINERS.
+
+* Document the driver in Documentation/hwmon/<driver_name>.
+
+* Add the driver to Kconfig and Makefile in alphabetical order.
+
+* Make sure that all dependencies are listed in Kconfig. For new drivers, it
+  is most likely prudent to add a dependency on EXPERIMENTAL.
+
+* Avoid forward declarations if you can. Rearrange the code if necessary.
+
+* Avoid calculations in macros and macro-generated functions. While such macros
+  may save a line or so in the source, it obfuscates the code and makes code
+  review more difficult. It may also result in code which is more complicated
+  than necessary. Use inline functions or just regular functions instead.
+
+* If the driver has a detect function, make sure it is silent. Debug messages
+  and messages printed after a successful detection are acceptable, but it
+  must not print messages such as "Chip XXX not found/supported".
+
+  Keep in mind that the detect function will run for all drivers supporting an
+  address if a chip is detected on that address. Unnecessary messages will just
+  pollute the kernel log and not provide any value.
+
+* Provide a detect function if and only if a chip can be detected reliably.
+
+* Avoid writing to chip registers in the detect function. If you have to write,
+  only do it after you have already gathered enough data to be certain that the
+  detection is going to be successful.
+
+  Keep in mind that the chip might not be what your driver believes it is, and
+  writing to it might cause a bad misconfiguration.
+
+* Make sure there are no race conditions in the probe function. Specifically,
+  completely initialize your chip first, then create sysfs entries and register
+  with the hwmon subsystem.
+
+* Do not provide support for deprecated sysfs attributes.
+
+* Do not create non-standard attributes unless really needed. If you have to use
+  non-standard attributes, or you believe you do, discuss it on the mailing list
+  first. Either case, provide a detailed explanation why you need the
+  non-standard attribute(s).
+  Standard attributes are specified in Documentation/hwmon/sysfs-interface.
+
+* When deciding which sysfs attributes to support, look at the chip's
+  capabilities. While we do not expect your driver to support everything the
+  chip may offer, it should at least support all limits and alarms.
+
+* Last but not least, please check if a driver for your chip already exists
+  before starting to write a new driver. Especially for temperature sensors,
+  new chips are often variants of previously released chips. In some cases,
+  a presumably new chip may simply have been relabeled.