Public bug reported:
[Problem description]
Kernel 4.17 introduced a new interface to set charge thresholds: The interface
remained unchanged with 4.18. There's a bug preventing writing the charge
thresholds for the secondary battery (BAT1).
[Impact]
ThinkPads with two batteries (ThinkPad "power bridge") e.g.
X240, T440(s), X250, T450(s), X260, T460(s), X270, T470(s) et al.
[Steps to reproduce]
echo 42 > /sys/class/power_supply/BAT1/charge_start_threshold
bash: echo: write error: No such device
echo 42 > /sys/class/power_supply/BAT0/charge_start_threshold
-- primary battery works!
[Fix]
Problem was fixed in 4.19:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/drivers/platform/x86/thinkpad_acpi.c?h=v4.19.15&id=d22296d9c38fd29a96bb5079fb8d17cee278f40e
I propose to cherry-pick the patch for 4.18.
[Test Case]
See above, a patched 4.18 works for T450s.
[Regression Potential]
Low. This patch only applies to several ThinkPad machines, and after applying
this patch, charge_start/stop_threshold work for BAT0 and BAT.
** Affects: linux-hwe (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1812099
Title:
4.18.0 thinkpad_acpi : thresholds for BAT1 not writable
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