In the librem5 branch we have a minimal workaround for cpuidle on top of mainline ATF. The GPC SIP call's definition of that workaround is now used as part of the DVFS devfreq implementation in mainline Linux.
@angus.ainslie I know we currently don't use this, but this allows us to put both cpuidle workarounds in Linux and be able to switch ATF (uboot) under the same kernel. This should make testing suspend/resume easier. In Linux we just make Abel's workaround compatible with devfreq (mainline linux): martin.kepplinger/linux-next@459ab3ce