[plasmashell] [Bug 507456] Powerdevil slows down login due to timeout with dccutil execution

https://bugs.kde.org/show_bug.cgi?id=507456

--- Comment #17 from Mauro <[email protected]> ---
Follow-up: I found a working config-based workaround on Kubuntu 26.04 (ddcutil
2.2.6, Plasma 6.6.6).

Note that my earlier statement that ddcutilrc tweaks "had no effect" was
actually wrong: the options were silently rejected because I was using the
pre-2.0 key = value syntax, which is invalid in ddcutil 2.2.x. With the correct
2.2.x syntax the options are applied.

This ~/.config/ddcutil/ddcutilrc:

[libddcutil]
options : --skip-ddc-checks --disable-dynamic-sleep --sleep-multiplier 0.15

drops detection from ~12.4 s to 0.21 s:

$ time ddcutil detect
  ddcutil detect  0,01s user 0,20s system 99% cpu 0,207 total

Both DisplayPort monitors are still detected, and DDC brightness control from
the Plasma "Brightness & Color" widget keeps working normally. The only visible
side effect is VCP version: Detection failed in ddcutil detect output, which is
cosmetic and caused by --skip-ddc-checks.

So the default-config slowdown is clearly in libddcutil's probing of these
DisplayPort monitors (the DDCRC_READ_ALL_ZERO retries on features 0xdd/0x41
with dynamic sleep). Disabling dynamic sleep and lowering the sleep multiplier
sidesteps it entirely, which points again at ddcutil itself rather than
powerdevil.

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