There is a single Q-Channel for clock gating the GIC-600 Distributor. The Q-Channel interface denies access if the Distributor block is busy processing interrupts.
The Distributor also has a separate Q-Channel that enables power control for each configured ITS. The Q-Channel reads GITS_CTLR.Quiescent to check whether the ITS is fully disabled. If the Quiescent bit is set, the Q-Channel qacceptn_its signal is asserted, and the GIC guarantees that the bus to the relevant ITS is idle in both directions and that the ITS can be powered down. To perform wake-on-LPI functionality, you can use GITS_FCTLR.PWE to disable the bus while the ITS is still active and able to translate interrupts. If the bus is disabled, the system must re-enable the bus based on the status of the ITS qactive signal, that is, when qactive_its is not asserted.
NoteThe qreqn* signals are synchronized internally, and can be driven asynchronously. See Power control signals.
For more information, see AMBA® Low Power Interface Specification, Arm® Q‑Channel and P‑Channel Interfaces.