[PATCH v5 5/5] Documentation:powerpc: Add device-tree bindings for power-mgt

[Gautham R. Shenoy]

From: "Gautham R. Shenoy" <ego@xxxxxxxxxxxxxxxxxx>

Document the device-tree bindings defining the the properties under
the @power-mgt node in the device tree that describe the idle states
for Linux running on baremetal POWER servers.

Signed-off-by: Gautham R. Shenoy <ego@xxxxxxxxxxxxxxxxxx>
---
[v4]-> [v5]: Fixed a couple of typos.

 .../devicetree/bindings/powerpc/opal/power-mgt.txt | 125 +++++++++++++++++++++
 1 file changed, 125 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/powerpc/opal/power-mgt.txt

diff --git a/Documentation/devicetree/bindings/powerpc/opal/power-mgt.txt b/Documentation/devicetree/bindings/powerpc/opal/power-mgt.txt
new file mode 100644
index 0000000..4967831
--- /dev/null
+++ b/Documentation/devicetree/bindings/powerpc/opal/power-mgt.txt
@@ -0,0 +1,125 @@
+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 optional unless mentioned otherwise below.
+
+- 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. This
+	property is required on POWER9 whenever
+	ibm,cpu-idle-state-names is defined and the length of this
+	property array should be the same as
+	ibm,-cpu-idle-state-names.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 */
+		0x00020000 /* This is a fast-sleep state */
+		0x00040000 /* This is a winkle state */
+		0x00080000 /* This is a fast-sleep state which requires a */
+			   /* software workaround for restoring the timebase*/
+		0x00800000 /* This state uses SPR PMICR instruction */
+		0x00100000 /* This is a fast stop state */
+		0x00200000 /* This is a deep-stop state */
+
+- 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. This property is required whenever
+	ibm,cpu-idle-state-names is defined and the length of this
+	property array should be the same as
+	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. On POWER9 this property must be defined if
+	ibm,cpu-idle-state-names is defined and the length should be
+	same as that of ibm,cpu-idle-state-names.
+
+- 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 whenever
+	ibm,cpu-idle-state-names is defined and the length of this
+	property array should be the same as
+	ibm,cpu-idle-state-names.
+
+- 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 whenever ibm,cpu-idle-state-names is
+	defined and the length of this property array should be the
+	same as ibm,cpu-idle-state-names.
+
+	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. When present on POWER8, the length of this property
+	array should be the same as ibm,cpu-idle-state-names.
+
+- 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. When present on
+	POWER8, the length of this property array should be the same
+	as ibm,cpu-idle-state-names.
-- 
1.9.4