Quoting Dr. Nikolaus Klepp (dr.klepp@???):

> Hi!
>
> I've found another strange thing after upgradeing to beowulf:
> thinkpad_acpi floods dmesg with these messages:
>
> [ 21.025368] thinkpad_acpi: acpi_evalf(BCSG, dd, ...) failed: AE_NOT_FOUND
> [ 21.025372] ACPI: \_SB_.PCI0.LPC_.EC__.HKEY: BCSG: evaluate failed
> [ 22.841660] thinkpad_acpi: acpi_evalf(BCTG, dd, ...) failed: AE_NOT_FOUND
> [ 22.841668] ACPI: \_SB_.PCI0.LPC_.EC__.HKEY: BCTG: evaluate failed
> [ 22.841702] thinkpad_acpi: acpi_evalf(BCSG, dd, ...) failed: AE_NOT_FOUND
> [ 22.841705] ACPI: \_SB_.PCI0.LPC_.EC__.HKEY: BCSG: evaluate failed
> [ 23.665919] thinkpad_acpi: acpi_evalf(BCTG, dd, ...) failed: AE_NOT_FOUND
> [ 23.665928] ACPI: \_SB_.PCI0.LPC_.EC__.HKEY: BCTG: evaluate failed
> [ 23.665964] thinkpad_acpi: acpi_evalf(BCSG, dd, ...) failed: AE_NOT_FOUND
> [ 23.665967] ACPI: \_SB_.PCI0.LPC_.EC__.HKEY: BCSG: evaluate failed
> [ 29.129438] thinkpad_acpi: acpi_evalf(BCTG, dd, ...) failed: AE_NOT_FOUND
> [ 29.129456] ACPI: \_SB_.PCI0.LPC_.EC__.HKEY: BCTG: evaluate failed
> [ 29.129537] thinkpad_acpi: acpi_evalf(BCSG, dd, ...) failed: AE_NOT_FOUND
>
> This was not the case on ascii. Does anybody know how to stop this -
> despite downgrading to kernel 4.9 ?

I don't have your answer, but I have partial information: BCSG is short
for BatteryCharge Capacity Threshold, which is one component of the ACPI
information being monitored. Details:
https://lore.kernel.org/patchwork/patch/858076/
https://www.reddit.com/r/thinkpad/comments/7hde0c/patch_for_linux_kernel_to_support_start_and_stop/

I'll bet something in thinkpad_acpi is trying to parse information from
the hardware and failing concerning that one datum, and grumbling about
the fact in dmesg (i.e., your pre-beowulf kernel didn't try to parse BCTG
information, lacking the code patch to add that functionality to
thinkpad_acpi, while the beowulf one tries and fails). I'll also bet
that it doesn't really matter, though I'm no expert at the details of
ACPI in ThinkPads.

It might be that updating your system BIOS would make this go away,
though that's pure speculation on my part.