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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
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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