--- /dev/null
+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.
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