Message-Id: <20240904-power-supply-extensions-v3-0-62efeb93f8ec@weissschuh.net>
Date: Wed, 04 Sep 2024 21:25:33 +0200
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Sebastian Reichel <sre@...nel.org>, Armin Wolf <W_Armin@....de>, 
 Hans de Goede <hdegoede@...hat.com>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH RFC v3 0/9] power: supply: extension API

Introduce a mechanism for drivers to extend the properties implemented
by a power supply.

Motivation
----------

Various drivers, mostly in platform/x86 extend the ACPI battery driver
with additional sysfs attributes to implement more UAPIs than are
exposed through ACPI by using various side-channels, like WMI,
nonstandard ACPI or EC communication.

While the created sysfs attributes look similar to the attributes
provided by the powersupply core, there are various deficiencies:

* They don't show up in uevent payload.
* They can't be queried with the standard in-kernel APIs.
* They don't work with triggers.
* The extending driver has to reimplement all of the parsing,
  formatting and sysfs display logic.
* Writing a extension driver is completely different from writing a
  normal power supply driver.
* ~Properties can not be properly overriden.~
  (Overriding is now explicitly forbidden)

The proposed extension API avoids all of these issues.
An extension is just a "struct power_supply_ext" with the same kind of
callbacks as in a normal "struct power_supply_desc".

The API is meant to be used via battery_hook_register(), the same way as
the current extensions.

When testing, please enable lockdep to make sure the locking is correct.

Contents
--------

* Patch 1 to 5 are preparation patches.
* Patch 6 implements the extension API itself.
* Patch 7 implements a locking scheme for the extension API.
* Patch 8 adds extension support to test_power.c
* Patch 9 converts the in-tree cros_charge-control driver to the
  extension API.

Open issues
-----------

* Newly registered properties will not show up in hwmon.
  To do that properly would require some changes in the hwmon core.
  As far as I know, no current driver would extend the hwmon properties anyways.
* As this is only useful with the hooks of CONFIG_ACPI_BATTERY, should
  it also be gated behind this or another config?
* Is an rw_semaphore acceptable?

[0] https://lore.kernel.org/lkml/20240528-cros_ec-charge-control-v2-0-81fb27e1cff4@weissschuh.net/

Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
---
Changes in v3:
- Make naming more consistent
- Readd locking
- Allow multiple active extensions
- Allow passing a "void *ext_data" when registering
- Switch example driver from system76 to cros_charge-control
- Link to v2: https://lore.kernel.org/r/20240608-power-supply-extensions-v2-0-2dcd35b012ad@weissschuh.net

Changes in v2:
- Drop locking patch, let's figure out the API first
- Allow registration of multiple extensions
- Pass extension to extension callbacks as parameter
- Disallow property overlap between extensions and core psy
- Drop system76/pdx86 maintainers, as the system76 changes are only RFC
  state anyways
- Link to v1: https://lore.kernel.org/r/20240606-power-supply-extensions-v1-0-b45669290bdc@weissschuh.net

---
Thomas Weißschuh (9):
      power: supply: core: rename psy_has_property() to psy_desc_has_property()
      power: supply: core: register thermal zone for battery
      power: supply: hwmon: register battery properties
      power: supply: sysfs: register battery properties
      power: supply: sysfs: rework uevent property loop
      power: supply: core: implement extension API
      power: supply: core: add locking around extension access
      power: supply: test-power: implement a power supply extension
      power: supply: cros_charge-control: use power_supply extensions

 drivers/power/supply/cros_charge-control.c | 207 +++++++++++------------------
 drivers/power/supply/power_supply.h        |  18 +++
 drivers/power/supply/power_supply_core.c   | 169 +++++++++++++++++++++--
 drivers/power/supply/power_supply_hwmon.c  |  52 ++++----
 drivers/power/supply/power_supply_leds.c   |   2 +
 drivers/power/supply/power_supply_sysfs.c  |  65 +++++----
 drivers/power/supply/test_power.c          | 104 +++++++++++++++
 include/linux/power_supply.h               |  33 +++++
 8 files changed, 453 insertions(+), 197 deletions(-)
---
base-commit: d8abb73f584772eaafa95a447c90f1c02dba0dec
change-id: 20240602-power-supply-extensions-07d949f509d9

Best regards,
-- 
Thomas Weißschuh <linux@...ssschuh.net>

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