[PATCH 0/3] platform/x86: Battery charge mode in toshiba_acpi

[Arvid Norlander <lkml@vorpal.se>]

This is an improved version of the battery charge control for Toshiba
Satellite Z830. The full background is available in the two emails linked
below, but a short summary will follow, including only what is relevant
for battery charge control.


Background (from link 1)
==========

The Toshiba Satellite/Portege Z830 supports not charging the battery fully
in order to prolong battery life. Unlike for example ThinkPads where this
control is granular here it is just off/on. When off it charges to 100%.
When on it charges to about 80%.

According to the Windows program used to control the feature the setting
will not take effect until the battery has been discharged to around 50%.
However, in my testing it takes effect as soon as the charge drops below
80%. On Windows Toshiba branded this feature as "Eco charging"

In the following example ACPI calls I will use the following newly defined
constants:
#define HCI_BATTERY_CHARGE_MODE 0xba
#define BATTERY_CHARGE_FULL 0
#define BATTERY_CHARGE_80_PERCENT 1

To set the feature:
  {HCI_SET, HCI_BATTERY_CHARGE_MODE, charge_mode, 0, 0, 0}
To query for the existence of the feature:
  {HCI_GET, HCI_BATTERY_CHARGE_MODE, 0, 0, 0, 0}
To read the feature:
  {HCI_GET, HCI_BATTERY_CHARGE_MODE, 0, 0, 0, 1}

The read may need to be retried if TOS_DATA_NOT_AVAILABLE is returned as
the status code. This rarely happens (I have never observed it on Linux),
but I have seen it happen under Windows once, and the software did retry
it.


Improvements
============

As discussed in link 2 & 3 below, the original approach was suboptimal.

This patch series instead consists of two patches.

The first patch implements detecting the feature as well as internal
getter/setter methods.

The second patch adds battery hooks (heavily based on the code for this in
thinkpad_acpi) which creates the standard charge_control_end_threshold file
under /sys/class/power_supply/BAT1.

Side note: There is no BAT0 on this Toshiba, I'm not sure why the numbering
ends up starting from 1 instead of 0 here. This differs from my Thinkpads,
where the numbering starts from 0, with BAT1 being the second battery.
However, I haven't spent much effort investigating this, as it did not seem
important.

Patch 3 updates the ABI test documentation as suggested by Hans de Goede.
Note that only the charge_control_end_threshold is updated, as this is the
only limit supported by the Toshiba Z830. Possibly
charge_control_start_threshold should also be updated similarly, or would
it be better to wait for an actual example of this in the wild first?

Link (1): https://www.spinics.net/lists/platform-driver-x86/msg34314.html
Link (2): https://www.spinics.net/lists/platform-driver-x86/msg34354.html
Link (3): https://www.spinics.net/lists/platform-driver-x86/msg34320.html

Arvid Norlander (3):
  platform/x86: Battery charge mode in toshiba_acpi (internals)
  platform/x86: Battery charge mode in toshiba_acpi (sysfs)
  docs: ABI: charge_control_end_threshold may not support all values

 Documentation/ABI/testing/sysfs-class-power |   5 +-
 drivers/platform/x86/toshiba_acpi.c         | 162 ++++++++++++++++++++
 2 files changed, 166 insertions(+), 1 deletion(-)


base-commit: 1c23f9e627a7b412978b4e852793c5e3c3efc555
-- 
2.37.2