150 lines
6.7 KiB
ReStructuredText
150 lines
6.7 KiB
ReStructuredText
How to Get Your Patch Accepted Into the Hwmon Subsystem
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=======================================================
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This text is a collection of suggestions for people writing patches or
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drivers for the hwmon subsystem. Following these suggestions will greatly
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increase the chances of your change being accepted.
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1. General
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----------
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* It should be unnecessary to mention, but please read and follow:
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- Documentation/process/submit-checklist.rst
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- Documentation/process/submitting-patches.rst
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- Documentation/process/coding-style.rst
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* Please run your patch through 'checkpatch --strict'. There should be no
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errors, no warnings, and few if any check messages. If there are any
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messages, please be prepared to explain.
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* Please use the standard multi-line comment style. Do not mix C and C++
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style comments in a single driver (with the exception of the SPDX license
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identifier).
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* If your patch generates checkpatch errors, warnings, or check messages,
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please refrain from explanations such as "I prefer that coding style".
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Keep in mind that each unnecessary message helps hiding a real problem,
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and a consistent coding style makes it easier for others to understand
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and review the code.
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* Please test your patch thoroughly. We are not your test group.
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Sometimes a patch can not or not completely be tested because of missing
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hardware. In such cases, you should test-build the code on at least one
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architecture. If run-time testing was not achieved, it should be written
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explicitly below the patch header.
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* If your patch (or the driver) is affected by configuration options such as
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CONFIG_SMP, make sure it compiles for all configuration variants.
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2. Adding functionality to existing drivers
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-------------------------------------------
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* Make sure the documentation in Documentation/hwmon/<driver_name>.rst is up to
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date.
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* Make sure the information in Kconfig is up to date.
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* If the added functionality requires some cleanup or structural changes, split
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your patch into a cleanup part and the actual addition. This makes it easier
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to review your changes, and to bisect any resulting problems.
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* Never mix bug fixes, cleanup, and functional enhancements in a single patch.
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3. New drivers
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--------------
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* Running your patch or driver file(s) through checkpatch does not mean its
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formatting is clean. If unsure about formatting in your new driver, run it
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through Lindent. Lindent is not perfect, and you may have to do some minor
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cleanup, but it is a good start.
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* Consider adding yourself to MAINTAINERS.
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* Document the driver in Documentation/hwmon/<driver_name>.rst.
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* Add the driver to Kconfig and Makefile in alphabetical order.
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* Make sure that all dependencies are listed in Kconfig.
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* Please list include files in alphabetic order.
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* Please align continuation lines with '(' on the previous line.
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* Avoid forward declarations if you can. Rearrange the code if necessary.
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* Avoid macros to generate groups of sensor attributes. It not only confuses
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checkpatch, but also makes it more difficult to review the code.
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* Avoid calculations in macros and macro-generated functions. While such macros
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may save a line or so in the source, it obfuscates the code and makes code
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review more difficult. It may also result in code which is more complicated
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than necessary. Use inline functions or just regular functions instead.
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* Limit the number of kernel log messages. In general, your driver should not
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generate an error message just because a runtime operation failed. Report
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errors to user space instead, using an appropriate error code. Keep in mind
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that kernel error log messages not only fill up the kernel log, but also are
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printed synchronously, most likely with interrupt disabled, often to a serial
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console. Excessive logging can seriously affect system performance.
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* Use devres functions whenever possible to allocate resources. For rationale
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and supported functions, please see Documentation/driver-api/driver-model/devres.rst.
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If a function is not supported by devres, consider using devm_add_action().
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* If the driver has a detect function, make sure it is silent. Debug messages
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and messages printed after a successful detection are acceptable, but it
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must not print messages such as "Chip XXX not found/supported".
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Keep in mind that the detect function will run for all drivers supporting an
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address if a chip is detected on that address. Unnecessary messages will just
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pollute the kernel log and not provide any value.
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* Provide a detect function if and only if a chip can be detected reliably.
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* Only the following I2C addresses shall be probed: 0x18-0x1f, 0x28-0x2f,
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0x48-0x4f, 0x58, 0x5c, 0x73 and 0x77. Probing other addresses is strongly
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discouraged as it is known to cause trouble with other (non-hwmon) I2C
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chips. If your chip lives at an address which can't be probed then the
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device will have to be instantiated explicitly (which is always better
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anyway.)
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* Avoid writing to chip registers in the detect function. If you have to write,
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only do it after you have already gathered enough data to be certain that the
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detection is going to be successful.
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Keep in mind that the chip might not be what your driver believes it is, and
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writing to it might cause a bad misconfiguration.
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* Make sure there are no race conditions in the probe function. Specifically,
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completely initialize your chip and your driver first, then register with
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the hwmon subsystem.
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* Use devm_hwmon_device_register_with_info() or, if your driver needs a remove
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function, hwmon_device_register_with_info() to register your driver with the
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hwmon subsystem. Try using devm_add_action() instead of a remove function if
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possible. Do not use hwmon_device_register().
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* Your driver should be buildable as module. If not, please be prepared to
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explain why it has to be built into the kernel.
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* Do not provide support for deprecated sysfs attributes.
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* Do not create non-standard attributes unless really needed. If you have to use
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non-standard attributes, or you believe you do, discuss it on the mailing list
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first. Either case, provide a detailed explanation why you need the
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non-standard attribute(s).
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Standard attributes are specified in Documentation/hwmon/sysfs-interface.rst.
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* When deciding which sysfs attributes to support, look at the chip's
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capabilities. While we do not expect your driver to support everything the
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chip may offer, it should at least support all limits and alarms.
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* Last but not least, please check if a driver for your chip already exists
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before starting to write a new driver. Especially for temperature sensors,
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new chips are often variants of previously released chips. In some cases,
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a presumably new chip may simply have been relabeled.
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