devfreq bandwidth management
related: https://source.puri.sm/Librem5/linux-next/issues/168 https://source.puri.sm/Librem5/use-cases/issues/75
There is bandwidth management implemented by Leonard, using perf: https://lore.kernel.org/linux-pm/a25094eac4c0f740e0e33c04af699b39a4226a08.1573252696.git.leonard.crestez@nxp.com/
I tested this and it does what it says, clocking down to 100mhz when appropriate. 100mhz produce display-glitches though, so that we can't use it.
you can test this without running the above changes, by using the userspace governor we currently use:
echo simple_ondemand > /sys/class/devfreq/3d400000.memory-controller/governor
echo 100000000 > /sys/class/devfreq/3d400000.memory-controller/userspace/set_freq