xref: /kernel/linux/linux-5.10/Documentation/devicetree/bindings/powerpc/opal/power-mgt.txt

IBM Power-Management Bindings
=============================

Linux running on baremetal POWER machines has access to the processor
idle states. The description of these idle states is exposed via the
node @power-mgt in the device-tree by the firmware.

Definitions:
----------------
Typically each idle state has the following associated properties:

- name: The name of the idle state as defined by the firmware.

- flags: indicating some aspects of this idle states such as the
         extent of state-loss, whether timebase is stopped on this
         idle states and so on. The flag bits are as follows:

- exit-latency: The latency involved in transitioning the state of the
		CPU from idle to running.

- target-residency: The minimum time that the CPU needs to reside in
		    this idle state in order to accrue power-savings
		    benefit.

Properties
----------------
The following properties provide details about the idle states. These
properties are exposed as arrays. Each entry in the property array
provides the value of that property for the idle state associated with
the array index of that entry.

If idle-states are defined, then the properties
"ibm,cpu-idle-state-names" and "ibm,cpu-idle-state-flags" are
required. The other properties are required unless mentioned
otherwise. The length of all the property arrays must be the same.

- ibm,cpu-idle-state-names:
	Array of strings containing the names of the idle states.

- ibm,cpu-idle-state-flags:
	Array of unsigned 32-bit values containing the values of the
	flags associated with the the aforementioned idle-states. The
	flag bits are as follows:
		0x00000001 /* Decrementer would stop */
		0x00000002 /* Needs timebase restore */
		0x00001000 /* Restore GPRs like nap */
		0x00002000 /* Restore hypervisor resource from PACA pointer */
		0x00004000 /* Program PORE to restore PACA pointer */
		0x00010000 /* This is a nap state (POWER7,POWER8) */
		0x00020000 /* This is a fast-sleep state (POWER8)*/
		0x00040000 /* This is a winkle state (POWER8) */
		0x00080000 /* This is a fast-sleep state which requires a */
			   /* software workaround for restoring the */
			   /* timebase (POWER8) */
		0x00800000 /* This state uses SPR PMICR instruction */
			   /* (POWER8)*/
		0x00100000 /* This is a fast stop state (POWER9) */
		0x00200000 /* This is a deep-stop state (POWER9) */

- ibm,cpu-idle-state-latencies-ns:
	Array of unsigned 32-bit values containing the values of the
	exit-latencies (in ns) for the idle states in
	ibm,cpu-idle-state-names.

- ibm,cpu-idle-state-residency-ns:
	Array of unsigned 32-bit values containing the values of the
	target-residency (in ns) for the idle states in
	ibm,cpu-idle-state-names. On POWER8 this is an optional
	property. If the property is absent, the target residency for
	the "Nap", "FastSleep" are defined to 10000 and 300000000
	respectively by the kernel. On POWER9 this property is required.

- ibm,cpu-idle-state-psscr:
	Array of unsigned 64-bit values containing the values for the
	PSSCR for each of the idle states in ibm,cpu-idle-state-names.
	This property is required on POWER9 and absent on POWER8.

- ibm,cpu-idle-state-psscr-mask:
	Array of unsigned 64-bit values containing the masks
	indicating which psscr fields are set in the corresponding
	entries of ibm,cpu-idle-state-psscr. This property is
	required on POWER9 and absent on POWER8.

	Whenever the firmware sets an entry in
	ibm,cpu-idle-state-psscr-mask value to 0xf, it implies that
	only the Requested Level (RL) field of the corresponding entry
	in ibm,cpu-idle-state-psscr should be considered by the
	kernel. For such idle states, the kernel would set the
	remaining fields of the psscr to the following sane-default
	values.

		- ESL and EC bits are to 1. So wakeup from any stop
		  state will be at vector 0x100.

		- MTL and PSLL are set to the maximum allowed value as
		  per the ISA, i.e. 15.

		- The Transition Rate, TR is set to the Maximum value
                  3.

	For all the other values of the entry in
	ibm,cpu-idle-state-psscr-mask, the kernel expects all the
	psscr fields of the corresponding entry in
	ibm,cpu-idle-state-psscr to be correctly set by the firmware.

- ibm,cpu-idle-state-pmicr:
	Array of unsigned 64-bit values containing the pmicr values
	for the idle states in ibm,cpu-idle-state-names. This 64-bit
	register value is to be set in pmicr for the corresponding
	state if the flag indicates that pmicr SPR should be set. This
	is an optional property on POWER8 and is absent on
	POWER9.

- ibm,cpu-idle-state-pmicr-mask:
	Array of unsigned 64-bit values containing the mask indicating
	which of the fields of the PMICR are set in the corresponding
	entries in ibm,cpu-idle-state-pmicr. This is an optional
	property on POWER8 and is absent on POWER9.