System Control and Power Interface (SCPI) Message Protocol ---------------------------------------------------------- Firmware implementing the SCPI described in ARM document number ARM DUI 0922B ("ARM Compute Subsystem SCP: Message Interface Protocols")[0] can be used by Linux to initiate various system control and power operations. Required properties: - compatible : should be * "arm,scpi" : For implementations complying to SCPI v1.0 or above * "arm,scpi-pre-1.0" : For implementations complying to all unversioned releases prior to SCPI v1.0 - mboxes: List of phandle and mailbox channel specifiers All the channels reserved by remote SCP firmware for use by SCPI message protocol should be specified in any order - 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. Clock bindings for the clocks based on SCPI Message Protocol ------------------------------------------------------------ This binding uses the common clock binding[1]. Container Node ============== Required properties: - compatible : should be "arm,scpi-clocks" All the clocks provided by SCP firmware via SCPI message protocol much be listed as sub-nodes under this node. Sub-nodes ========= Required properties: - compatible : shall include one of the following "arm,scpi-dvfs-clocks" - all the clocks that are variable and index based. These clocks don't provide an entire range of values between the limits but only discrete points within the range. The firmware provides the mapping for each such operating frequency and the index associated with it. The firmware also manages the voltage scaling appropriately with the clock scaling. "arm,scpi-variable-clocks" - all the clocks that are variable and provide full range within the specified range. The firmware provides the range of values within a specified range. Other required properties for all clocks(all from common clock binding): - #clock-cells : Should be 1. Contains the Clock ID value used by SCPI commands. - clock-output-names : shall be the corresponding names of the outputs. - 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 into the clock-output-names array. SRAM and Shared Memory for SCPI ------------------------------- A small area of SRAM is reserved for SCPI 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 SCPI. 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 Sensor bindings for the sensors based on SCPI Message Protocol -------------------------------------------------------------- SCPI provides an API to access the various sensors on the SoC. Required properties: - compatible : should be "arm,scpi-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. Power domain bindings for the power domains based on SCPI 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 SCPI commands. - num-domains: Total number of power domains provided by SCPI. This is needed as the SCPI message protocol lacks a mechanism to query this information at runtime. PM domain consumers =================== Required properties: - power-domains : A phandle and PM domain specifier as defined by bindings of the power controller specified by phandle. [0] http://infocenter.arm.com/help/topic/com.arm.doc.dui0922b/index.html [1] Documentation/devicetree/bindings/clock/clock-bindings.txt [2] Documentation/devicetree/bindings/thermal/thermal.txt [3] Documentation/devicetree/bindings/sram/sram.yaml [4] Documentation/devicetree/bindings/power/power-domain.yaml 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>; }; scpi_protocol: scpi@2e000000 { compatible = "arm,scpi"; mboxes = <&mailbox 0 &mailbox 1>; shmem = <&cpu_scp_lpri &cpu_scp_hpri>; clocks { compatible = "arm,scpi-clocks"; scpi_dvfs: scpi_clocks@0 { compatible = "arm,scpi-dvfs-clocks"; #clock-cells = <1>; clock-indices = <0>, <1>, <2>; clock-output-names = "atlclk", "aplclk","gpuclk"; }; scpi_clk: scpi_clocks@3 { compatible = "arm,scpi-variable-clocks"; #clock-cells = <1>; clock-indices = <3>, <4>; clock-output-names = "pxlclk0", "pxlclk1"; }; }; scpi_sensors0: sensors { compatible = "arm,scpi-sensors"; #thermal-sensor-cells = <1>; }; scpi_devpd: scpi-power-domains { compatible = "arm,scpi-power-domains"; num-domains = <2>; #power-domain-cells = <1>; }; }; cpu@0 { ... reg = <0 0>; clocks = <&scpi_dvfs 0>; }; hdlcd@7ff60000 { ... reg = <0 0x7ff60000 0 0x1000>; clocks = <&scpi_clk 4>; power-domains = <&scpi_devpd 1>; }; thermal-zones { soc_thermal { polling-delay-passive = <100>; polling-delay = <1000>; /* sensor ID */ thermal-sensors = <&scpi_sensors0 3>; ... }; }; In the above example, the #clock-cells is set to 1 as required. scpi_dvfs has 3 output clocks namely: atlclk, aplclk, and gpuclk with 0, 1 and 2 as clock-indices. scpi_clk has 2 output clocks namely: pxlclk0 and pxlclk1 with 3 and 4 as clock-indices. The first consumer in the example is cpu@0 and it has '0' as the clock specifier which points to the first entry in the output clocks of scpi_dvfs i.e. "atlclk". Similarly the second example is hdlcd@7ff60000 and it has pxlclk1 as input clock. '4' in the clock specifier here points to the second entry in the output clocks of scpi_clocks i.e. "pxlclk1" The thermal-sensors property in the soc_thermal node uses the temperature sensor provided by SCP firmware to setup a thermal zone. The ID "3" is the sensor identifier for the temperature sensor as used by the firmware. The num-domains property in scpi-power-domains domain specifies that SCPI provides 2 power domains. The hdlcd node uses the power domain with domain ID 1.