Documentation/hwmon/submitting-patches - arm/linux - Git at Google

 	How to Get Your Patch Accepted Into the Hwmon Subsystem
 	-------------------------------------------------------

 This text 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/process/submit-checklist.rst
     Documentation/process/submitting-drivers.rst
     Documentation/process/submitting-patches.rst
     Documentation/process/coding-style.rst

 * Please run your patch through 'checkpatch --strict'. There should be no
   errors, no warnings, and few if any check messages. If there are any
   messages, please be prepared to explain.

 * If your patch generates checkpatch errors, warnings, or check messages,
   please refrain from explanations such as "I prefer that coding style".
   Keep in mind that each unnecessary message helps hiding a real problem,
   and a consistent coding style makes it easier for others to understand
   and review the code.

 * 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, 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.

 * Please list include files in alphabetic order.

 * Please align continuation lines with '(' on the previous line.

 * Avoid forward declarations if you can. Rearrange the code if necessary.

 * Avoid macros to generate groups of sensor attributes. It not only confuses
   checkpatch, but also makes it more difficult to review the code.

 * 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.

 * Limit the number of kernel log messages. In general, your driver should not
   generate an error message just because a runtime operation failed. Report
   errors to user space instead, using an appropriate error code. Keep in mind
   that kernel error log messages not only fill up the kernel log, but also are
   printed synchronously, most likely with interrupt disabled, often to a serial
   console. Excessive logging can seriously affect system performance.

 * Use devres functions whenever possible to allocate resources. For rationale
   and supported functions, please see Documentation/driver-model/devres.txt.
   If a function is not supported by devres, consider using devm_add_action().

 * 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.

 * Only the following I2C addresses shall be probed: 0x18-0x1f, 0x28-0x2f,
   0x48-0x4f, 0x58, 0x5c, 0x73 and 0x77. Probing other addresses is strongly
   discouraged as it is known to cause trouble with other (non-hwmon) I2C
   chips. If your chip lives at an address which can't be probed then the
   device will have to be instantiated explicitly (which is always better
   anyway.)

 * 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 and your driver first, then register with
   the hwmon subsystem.

 * Use devm_hwmon_device_register_with_groups() or, if your driver needs a remove
   function, hwmon_device_register_with_groups() to register your driver with the
   hwmon subsystem. Try using devm_add_action() instead of a remove function if
   possible. Do not use hwmon_device_register().

 * Your driver should be buildable as module. If not, please be prepared to
   explain why it has to be built into the kernel.

 * 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.
	How to Get Your Patch Accepted Into the Hwmon Subsystem
	-------------------------------------------------------

	This text 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/process/submit-checklist.rst
	Documentation/process/submitting-drivers.rst
	Documentation/process/submitting-patches.rst
	Documentation/process/coding-style.rst

	* Please run your patch through 'checkpatch --strict'. There should be no
	errors, no warnings, and few if any check messages. If there are any
	messages, please be prepared to explain.

	* If your patch generates checkpatch errors, warnings, or check messages,
	please refrain from explanations such as "I prefer that coding style".
	Keep in mind that each unnecessary message helps hiding a real problem,
	and a consistent coding style makes it easier for others to understand
	and review the code.

	* 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, 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.

	* Please list include files in alphabetic order.

	* Please align continuation lines with '(' on the previous line.

	* Avoid forward declarations if you can. Rearrange the code if necessary.

	* Avoid macros to generate groups of sensor attributes. It not only confuses
	checkpatch, but also makes it more difficult to review the code.

	* 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.

	* Limit the number of kernel log messages. In general, your driver should not
	generate an error message just because a runtime operation failed. Report
	errors to user space instead, using an appropriate error code. Keep in mind
	that kernel error log messages not only fill up the kernel log, but also are
	printed synchronously, most likely with interrupt disabled, often to a serial
	console. Excessive logging can seriously affect system performance.

	* Use devres functions whenever possible to allocate resources. For rationale
	and supported functions, please see Documentation/driver-model/devres.txt.
	If a function is not supported by devres, consider using devm_add_action().

	* 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.

	* Only the following I2C addresses shall be probed: 0x18-0x1f, 0x28-0x2f,
	0x48-0x4f, 0x58, 0x5c, 0x73 and 0x77. Probing other addresses is strongly
	discouraged as it is known to cause trouble with other (non-hwmon) I2C
	chips. If your chip lives at an address which can't be probed then the
	device will have to be instantiated explicitly (which is always better
	anyway.)

	* 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 and your driver first, then register with
	the hwmon subsystem.

	* Use devm_hwmon_device_register_with_groups() or, if your driver needs a remove
	function, hwmon_device_register_with_groups() to register your driver with the
	hwmon subsystem. Try using devm_add_action() instead of a remove function if
	possible. Do not use hwmon_device_register().

	* Your driver should be buildable as module. If not, please be prepared to
	explain why it has to be built into the kernel.

	* 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.