Documentation/devicetree/bindings/powerpc/opal/power-mgt.txt

Source file repositories/reference/linux-study-clean/Documentation/devicetree/bindings/powerpc/opal/power-mgt.txt

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Documentation/devicetree/bindings/powerpc/opal/power-mgt.txt
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Support Tooling And Documentation
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Documentation
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Support Tooling And Documentation: documentation
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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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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 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

Annotation

Implementation Notes