[RFC PATCH 1/8] Documentation: add DT binding for ARM System Control and Management Interface(SCMI) protocol

[Sudeep Holla]

This patch adds devicetree binding for System Control and Management
Interface (SCMI) Message Protocol used between the Application Cores(AP)
and the System Control Processor(SCP). The MHU peripheral provides a
mechanism for inter-processor communication between SCP's M3 processor
and AP.

SCP offers control and management of the core/cluster power states,
various power domain DVFS including the core/cluster, certain system
clocks configuration, thermal sensors and many others.

SCMI protocol is developed as better replacement to the existing SCPI
which is not flexible and easily extensible.

Cc: Rob Herring <robh+dt@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
---
 Documentation/devicetree/bindings/arm/arm,scmi.txt | 193 +++++++++++++++++++++
 1 file changed, 193 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/arm/arm,scmi.txt

diff --git a/Documentation/devicetree/bindings/arm/arm,scmi.txt b/Documentation/devicetree/bindings/arm/arm,scmi.txt
new file mode 100644
index 000000000000..d6e4b7eff199
--- /dev/null
+++ b/Documentation/devicetree/bindings/arm/arm,scmi.txt
@@ -0,0 +1,193 @@
+System Control and Management Interface (SCMI) Message Protocol
+----------------------------------------------------------
+
+The SCMI is intended to allow agents such as OSPM to manage various functions
+that are provided by the hardware platform it is running on, including power
+and performance functions.
+
+This binding is intended to define the interface the firmware implementing
+the SCMI as described in ARM document number ARM DUI 0922B ("ARM System Control
+and Management Interface Platform Design Document")[0] provide for OSPM in
+the device tree.
+
+Required properties:
+
+- compatible : shall be "arm,scmi"
+- method : The method of calling the SCMI firmware. Only permitted value
+	   currently is:
+	   "mailbox-doorbell" : When mailbox doorbell is used as a mechanism
+				to alert the presence of a messages and/or
+				notification
+- mboxes: List of phandle and mailbox channel specifiers. It should contain
+	  exactly one or two mailboxes, one for transmitting messages("tx")
+	  and another optional for receiving the notifications("rx") if
+	  supported.
+- mbox-names: shall be "tx" or "rx"
+- shmem : List of phandle pointing to the shared memory(SHM) area between the
+	  processors using these mailboxes for IPC, one for each mailbox
+	  SHM can be any memory reserved for the purpose of this communication
+	  between the processors.
+
+See Documentation/devicetree/bindings/mailbox/mailbox.txt for more details
+about the generic mailbox controller and client driver bindings.
+
+Each protocol supported shall have a sub-node with corresponding compatible
+as described in the following sections. If the platform supports dedicated
+communication channel for a particular protocol, the 3 properties namely:
+mboxes, mbox-names and shmem shall be present in the sub-node corresponding
+to that protocol.
+
+Clock/Performance bindings for the clocks/OPPs based on SCMI Message Protocol
+------------------------------------------------------------
+
+This binding uses the common clock binding[1].
+
+Required properties:
+- compatible : shall be "arm,scmi-clocks" or "arm,scmi-perf-domains"
+	arm,scmi-clocks:
+	       These clocks either provide an entire range of values
+	       between the limits or only discrete points each at fixed
+	       step size between the limits. The firmware provides
+	       mechanism to discover them.
+	arm,scmi-perf-domains:
+		These are OPPs(not just simple clocks), i.e. discrete
+		performance levels that are supported by the platform.
+		Again the firmware provides mechanism to discover the
+		performance and other attributes associated with the
+		levels.
+
+Other required properties for all clocks(all from common clock binding):
+- #clock-cells : Should be 1. Contains the Clock ID value used by SCMI commands.
+- clock-indices: The identifying number for the clocks(i.e.clock_id) in the
+	node. It can be non linear and hence provide the mapping of
+	identifiers.
+
+Power domain bindings for the power domains based on SCMI Message Protocol
+------------------------------------------------------------
+
+This binding uses the generic power domain binding[4].
+
+PM domain providers
+===================
+
+Required properties:
+ - #power-domain-cells : Should be 1. Contains the device or the power
+			 domain ID value used by SCMI commands.
+
+PM domain consumers
+===================
+
+Required properties:
+ - power-domains : A phandle and PM domain specifier as defined by bindings of
+                   the power controller specified by phandle.
+
+Sensor bindings for the sensors based on SCMI Message Protocol
+--------------------------------------------------------------
+SCMI provides an API to access the various sensors on the SoC.
+
+Required properties:
+- compatible : should be "arm,scmi-sensors".
+- #thermal-sensor-cells: should be set to 1. This property follows the
+			 thermal device tree bindings[2].
+
+			 Valid cell values are raw identifiers (Sensor ID)
+			 as used by the firmware. Refer to  platform details
+			 for your implementation for the IDs to use.
+
+SRAM and Shared Memory for SCMI
+-------------------------------
+
+A small area of SRAM is reserved for SCMI communication between application
+processors and SCP.
+
+The properties should follow the generic mmio-sram description found in [3]
+
+Each sub-node represents the reserved area for SCMI.
+
+Required sub-node properties:
+- reg : The base offset and size of the reserved area with the SRAM
+- compatible : should be "arm,scp-shmem" for Non-secure SRAM based
+	       shared memory
+
+[0] http://infocenter.arm.com/help/topic/com.arm.doc.den0056a/index.html
+[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
+[2] Documentation/devicetree/bindings/thermal/thermal.txt
+[3] Documentation/devicetree/bindings/sram/sram.txt
+[4] Documentation/devicetree/bindings/power/power_domain.txt
+
+Example:
+
+sram: sram@50000000 {
+	compatible = "arm,juno-sram-ns", "mmio-sram";
+	reg = <0x0 0x50000000 0x0 0x10000>;
+
+	#address-cells = <1>;
+	#size-cells = <1>;
+	ranges = <0 0x0 0x50000000 0x10000>;
+
+	cpu_scp_lpri: scp-shmem@0 {
+		compatible = "arm,juno-scp-shmem";
+		reg = <0x0 0x200>;
+	};
+
+	cpu_scp_hpri: scp-shmem@200 {
+		compatible = "arm,juno-scp-shmem";
+		reg = <0x200 0x200>;
+	};
+};
+
+mailbox: mailbox0@40000000 {
+	....
+	#mbox-cells = <1>;
+};
+
+scmi_protocol: scmi@2e000000 {
+	compatible = "arm,scmi";
+	mboxes = <&mailbox 0 &mailbox 1>;
+	shmem = <&cpu_scp_lpri &cpu_scp_hpri>;
+
+	scmi_dvfs: clocks@0 {
+		compatible = "arm,scmi-perf-domains";
+		#clock-cells = <1>;
+		clock-indices = <0>, <1>, <2>;
+	};
+	scmi_clk: clocks@3 {
+		compatible = "arm,scmi-clocks";
+		#clock-cells = <1>;
+		clock-indices = <3>, <4>;
+	};
+
+	scmi_sensors: sensors {
+		compatible = "arm,scmi-sensors";
+		#thermal-sensor-cells = <1>;
+	};
+
+	scmi_devpd: power-domains {
+		compatible = "arm,scmi-power-domains";
+		#power-domain-cells = <1>;
+	};
+};
+
+cpu@0 {
+	...
+	reg = <0 0>;
+	clocks = <&scmi_dvfs 0>;
+};
+
+hdlcd@7ff60000 {
+	...
+	reg = <0 0x7ff60000 0 0x1000>;
+	clocks = <&scmi_clk 4>;
+	power-domains = <&scmi_devpd 1>;
+};
+
+thermal-zones {
+	soc_thermal {
+		polling-delay-passive = <100>;
+		polling-delay = <1000>;
+
+				/* sensor         ID */
+		thermal-sensors = <&scmi_sensors0 3>;
+		...
+	};
+};
-- 
2.7.4