[PATCH v4 4/8] dt-bindings: arm: SCMI bindings documentation

[Etienne Carriere]

Dump SCMI DT bindings documentation from Linux kernel source
tree v5.8-rc1.

Signed-off-by: Etienne Carriere <etienne.carriere at linaro.org>
Reviewed-by: Simon Glass <sjg at chromium.org>
---

No change in v4.

No change in v3.

Changes in v2:
- No change but added R-b tag.
- Yet a question: do we need to add this binding doc in U-Boot
  since already existing in Linux DT bindings docs? Related to review
  comment https://www.mail-archive.com/u-boot@lists.denx.de/msg377725.html
---
 doc/device-tree-bindings/arm/arm,scmi.txt | 197 ++++++++++++++++++++++
 1 file changed, 197 insertions(+)
 create mode 100644 doc/device-tree-bindings/arm/arm,scmi.txt

diff --git a/doc/device-tree-bindings/arm/arm,scmi.txt b/doc/device-tree-bindings/arm/arm,scmi.txt
new file mode 100644
index 0000000000..1f293ea24c
--- /dev/null
+++ b/doc/device-tree-bindings/arm/arm,scmi.txt
@@ -0,0 +1,197 @@
+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 DEN 0056A ("ARM System Control
+and Management Interface Platform Design Document")[0] provide for OSPM in
+the device tree.
+
+Required properties:
+
+The scmi node with the following properties shall be under the /firmware/ node.
+
+- compatible : shall be "arm,scmi" or "arm,scmi-smc" for smc/hvc transports
+- 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.
+- shmem : List of phandle pointing to the shared memory(SHM) area as per
+	  generic mailbox client binding.
+- #address-cells : should be '1' if the device has sub-nodes, maps to
+	  protocol identifier for a given sub-node.
+- #size-cells : should be '0' as 'reg' property doesn't have any size
+	  associated with it.
+- arm,smc-id : SMC id required when using smc or hvc transports
+
+Optional properties:
+
+- mbox-names: shall be "tx" or "rx" depending on mboxes entries.
+
+See Documentation/devicetree/bindings/mailbox/mailbox.txt for more details
+about the generic mailbox controller and client driver bindings.
+
+The mailbox is the only permitted method of calling the SCMI firmware.
+Mailbox doorbell is used as a mechanism to alert the presence of a
+messages and/or notification.
+
+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:
+- #clock-cells : Should be 1. Contains the Clock ID value used by SCMI commands.
+
+Power domain bindings for the power domains based on SCMI Message Protocol
+------------------------------------------------------------
+
+This binding for the SCMI power domain providers uses the generic power
+domain binding[2].
+
+Required properties:
+ - #power-domain-cells : Should be 1. Contains the device or the power
+			 domain ID value used by SCMI commands.
+
+Sensor bindings for the sensors based on SCMI Message Protocol
+--------------------------------------------------------------
+SCMI provides an API to access the various sensors on the SoC.
+
+Required properties:
+- #thermal-sensor-cells: should be set to 1. This property follows the
+			 thermal device tree bindings[3].
+
+			 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.
+
+Reset signal bindings for the reset domains based on SCMI Message Protocol
+------------------------------------------------------------
+
+This binding for the SCMI reset domain providers uses the generic reset
+signal binding[5].
+
+Required properties:
+ - #reset-cells : Should be 1. Contains the reset domain ID value used
+		  by SCMI commands.
+
+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 [4]
+
+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,scmi-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/power/power-domain.yaml
+[3] Documentation/devicetree/bindings/thermal/thermal.txt
+[4] Documentation/devicetree/bindings/sram/sram.yaml
+[5] Documentation/devicetree/bindings/reset/reset.txt
+
+Example:
+
+sram at 50000000 {
+	compatible = "mmio-sram";
+	reg = <0x0 0x50000000 0x0 0x10000>;
+
+	#address-cells = <1>;
+	#size-cells = <1>;
+	ranges = <0 0x0 0x50000000 0x10000>;
+
+	cpu_scp_lpri: scp-shmem at 0 {
+		compatible = "arm,scmi-shmem";
+		reg = <0x0 0x200>;
+	};
+
+	cpu_scp_hpri: scp-shmem at 200 {
+		compatible = "arm,scmi-shmem";
+		reg = <0x200 0x200>;
+	};
+};
+
+mailbox at 40000000 {
+	....
+	#mbox-cells = <1>;
+	reg = <0x0 0x40000000 0x0 0x10000>;
+};
+
+firmware {
+
+	...
+
+	scmi {
+		compatible = "arm,scmi";
+		mboxes = <&mailbox 0 &mailbox 1>;
+		mbox-names = "tx", "rx";
+		shmem = <&cpu_scp_lpri &cpu_scp_hpri>;
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		scmi_devpd: protocol at 11 {
+			reg = <0x11>;
+			#power-domain-cells = <1>;
+		};
+
+		scmi_dvfs: protocol at 13 {
+			reg = <0x13>;
+			#clock-cells = <1>;
+		};
+
+		scmi_clk: protocol at 14 {
+			reg = <0x14>;
+			#clock-cells = <1>;
+		};
+
+		scmi_sensors0: protocol at 15 {
+			reg = <0x15>;
+			#thermal-sensor-cells = <1>;
+		};
+
+		scmi_reset: protocol at 16 {
+			reg = <0x16>;
+			#reset-cells = <1>;
+		};
+	};
+};
+
+cpu at 0 {
+	...
+	reg = <0 0>;
+	clocks = <&scmi_dvfs 0>;
+};
+
+hdlcd at 7ff60000 {
+	...
+	reg = <0 0x7ff60000 0 0x1000>;
+	clocks = <&scmi_clk 4>;
+	power-domains = <&scmi_devpd 1>;
+	resets = <&scmi_reset 10>;
+};
+
+thermal-zones {
+	soc_thermal {
+		polling-delay-passive = <100>;
+		polling-delay = <1000>;
+					/* sensor ID */
+		thermal-sensors = <&scmi_sensors0 3>;
+		...
+	};
+};
-- 
2.17.1