Power domains

The Linux PMU provider publishes seven generic power domains. Linux explicitly controls HP connectivity (HPCNNT) transitions; the other domains are exposed for topology and attachment and kept on by provider policy. Active-state radio PMU initialization still occurs in the linked payload.

Registered topology and policy

Domain name	Binding identifier	Registered parent	Linux policy
top	ESP32S31_PD_TOP	None	Always on
hp-alive	ESP32S31_PD_HPALIVE	top	Always on
modem-power	ESP32S31_PD_MODEMPWR	top	Always on
hp-cpu	ESP32S31_PD_HPCPU	top	Always on
hp-connectivity	ESP32S31_PD_HPCNNT	top	Automatic only when espressif,allow-hpcnnt-power-off is present
modem	ESP32S31_PD_MODEM	modem-power	Always on
lp-peripheral	ESP32S31_PD_LP_PERI	None registered	Always on

The supplied device tree includes the HPCNNT opt-in. The radio module holds a separate vote while active because the payload accesses this domain outside a normal device attachment. An active radio vote prevents HPCNNT power-off. After payload PMU initialization, the reclaim hook reapplies Linux’s HPCNNT force state. See the domain policy and topology, DTS opt-in, and vote/reclaim implementation.

Read domain diagnostics

for file in /sys/bus/platform/devices/*/domains; do
    [ -r "$file" ] && cat "$file"
done

Field	Meaning
Leading name	Domain name from the table above
policy=	always-on or automatic, from the genpd policy flag
software=	Provider’s tracked on / off state
hardware=	Force-register interpretation: off if FORCE_PD is set, otherwise on if FORCE_PU is set, otherwise firmware-auto
force=	Low six force-control bits: reset, isolation, power-up, no-reset, no-isolation, power-down
on=, off=	Successful genpd on/off callbacks; on also includes initial HPCNNT ownership at probe
reclaim=	Reclaim attempts after payload PMU initialization
errors=	Force-register readback failures during transitions
radio-vote=	Active radio veto for hp-connectivity; printed as zero for the other domains

Despite the field name, hardware= decodes a force-control register. It is not an independent power-good signal, current reading or proof of retention. The output format is defined by domains_show().

System retention configuration

The OpenSBI APPWR profile writes power value 0x0000aa00 and clock value 0x00000000. The source defines these as memory-retention mode for the four HP memory banks, power-down mode for HP logic groups and gating of HP clock classes. LP firmware supplies the wake request. See the profile constants and entry sequence.

For current suspend status, CPU idle, shutdown and timed deep sleep, see Power management.

Power measurements

Record the board revision, supply point/voltage, USB connection, enabled peripherals, radio state, CPU frequency and instrument/sample interval alongside each measurement. Board-input current includes regulators, USB bridges and LEDs; do not label it as CPU-domain current.