220 lines
7 KiB
Plaintext
Executable file
220 lines
7 KiB
Plaintext
Executable file
System Control and Power Interface (SCPI) Message Protocol
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----------------------------------------------------------
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Firmware implementing the SCPI described in ARM document number ARM DUI 0922B
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("ARM Compute Subsystem SCP: Message Interface Protocols")[0] can be used
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by Linux to initiate various system control and power operations.
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Required properties:
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- compatible : should be
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* "arm,scpi" : For implementations complying to SCPI v1.0 or above
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* "arm,scpi-pre-1.0" : For implementations complying to all
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unversioned releases prior to SCPI v1.0
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- mboxes: List of phandle and mailbox channel specifiers
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All the channels reserved by remote SCP firmware for use by
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SCPI message protocol should be specified in any order
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- shmem : List of phandle pointing to the shared memory(SHM) area between the
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processors using these mailboxes for IPC, one for each mailbox
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SHM can be any memory reserved for the purpose of this communication
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between the processors.
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See Documentation/devicetree/bindings/mailbox/mailbox.txt
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for more details about the generic mailbox controller and
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client driver bindings.
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Clock bindings for the clocks based on SCPI Message Protocol
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------------------------------------------------------------
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This binding uses the common clock binding[1].
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Container Node
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==============
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Required properties:
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- compatible : should be "arm,scpi-clocks"
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All the clocks provided by SCP firmware via SCPI message
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protocol much be listed as sub-nodes under this node.
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Sub-nodes
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=========
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Required properties:
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- compatible : shall include one of the following
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"arm,scpi-dvfs-clocks" - all the clocks that are variable and index based.
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These clocks don't provide an entire range of values between the
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limits but only discrete points within the range. The firmware
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provides the mapping for each such operating frequency and the
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index associated with it. The firmware also manages the
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voltage scaling appropriately with the clock scaling.
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"arm,scpi-variable-clocks" - all the clocks that are variable and provide full
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range within the specified range. The firmware provides the
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range of values within a specified range.
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Other required properties for all clocks(all from common clock binding):
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- #clock-cells : Should be 1. Contains the Clock ID value used by SCPI commands.
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- clock-output-names : shall be the corresponding names of the outputs.
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- clock-indices: The identifying number for the clocks(i.e.clock_id) in the
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node. It can be non linear and hence provide the mapping of identifiers
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into the clock-output-names array.
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SRAM and Shared Memory for SCPI
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-------------------------------
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A small area of SRAM is reserved for SCPI communication between application
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processors and SCP.
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The properties should follow the generic mmio-sram description found in [3]
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Each sub-node represents the reserved area for SCPI.
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Required sub-node properties:
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- reg : The base offset and size of the reserved area with the SRAM
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- compatible : should be "arm,scp-shmem" for Non-secure SRAM based
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shared memory
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Sensor bindings for the sensors based on SCPI Message Protocol
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--------------------------------------------------------------
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SCPI provides an API to access the various sensors on the SoC.
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Required properties:
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- compatible : should be "arm,scpi-sensors".
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- #thermal-sensor-cells: should be set to 1. This property follows the
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thermal device tree bindings[2].
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Valid cell values are raw identifiers (Sensor ID)
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as used by the firmware. Refer to platform details
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for your implementation for the IDs to use.
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Power domain bindings for the power domains based on SCPI Message Protocol
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------------------------------------------------------------
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This binding uses the generic power domain binding[4].
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PM domain providers
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===================
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Required properties:
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- #power-domain-cells : Should be 1. Contains the device or the power
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domain ID value used by SCPI commands.
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- num-domains: Total number of power domains provided by SCPI. This is
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needed as the SCPI message protocol lacks a mechanism to
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query this information at runtime.
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PM domain consumers
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===================
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Required properties:
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- power-domains : A phandle and PM domain specifier as defined by bindings of
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the power controller specified by phandle.
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[0] http://infocenter.arm.com/help/topic/com.arm.doc.dui0922b/index.html
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[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
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[2] Documentation/devicetree/bindings/thermal/thermal.txt
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[3] Documentation/devicetree/bindings/sram/sram.txt
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[4] Documentation/devicetree/bindings/power/power_domain.txt
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Example:
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sram: sram@50000000 {
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compatible = "arm,juno-sram-ns", "mmio-sram";
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reg = <0x0 0x50000000 0x0 0x10000>;
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#address-cells = <1>;
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#size-cells = <1>;
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ranges = <0 0x0 0x50000000 0x10000>;
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cpu_scp_lpri: scp-shmem@0 {
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compatible = "arm,juno-scp-shmem";
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reg = <0x0 0x200>;
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};
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cpu_scp_hpri: scp-shmem@200 {
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compatible = "arm,juno-scp-shmem";
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reg = <0x200 0x200>;
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};
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};
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mailbox: mailbox0@40000000 {
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....
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#mbox-cells = <1>;
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};
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scpi_protocol: scpi@2e000000 {
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compatible = "arm,scpi";
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mboxes = <&mailbox 0 &mailbox 1>;
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shmem = <&cpu_scp_lpri &cpu_scp_hpri>;
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clocks {
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compatible = "arm,scpi-clocks";
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scpi_dvfs: scpi_clocks@0 {
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compatible = "arm,scpi-dvfs-clocks";
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#clock-cells = <1>;
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clock-indices = <0>, <1>, <2>;
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clock-output-names = "atlclk", "aplclk","gpuclk";
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};
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scpi_clk: scpi_clocks@3 {
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compatible = "arm,scpi-variable-clocks";
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#clock-cells = <1>;
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clock-indices = <3>, <4>;
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clock-output-names = "pxlclk0", "pxlclk1";
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};
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};
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scpi_sensors0: sensors {
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compatible = "arm,scpi-sensors";
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#thermal-sensor-cells = <1>;
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};
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scpi_devpd: scpi-power-domains {
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compatible = "arm,scpi-power-domains";
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num-domains = <2>;
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#power-domain-cells = <1>;
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};
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};
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cpu@0 {
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...
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reg = <0 0>;
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clocks = <&scpi_dvfs 0>;
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};
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hdlcd@7ff60000 {
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...
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reg = <0 0x7ff60000 0 0x1000>;
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clocks = <&scpi_clk 4>;
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power-domains = <&scpi_devpd 1>;
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};
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thermal-zones {
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soc_thermal {
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polling-delay-passive = <100>;
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polling-delay = <1000>;
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/* sensor ID */
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thermal-sensors = <&scpi_sensors0 3>;
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...
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};
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};
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In the above example, the #clock-cells is set to 1 as required.
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scpi_dvfs has 3 output clocks namely: atlclk, aplclk, and gpuclk with 0,
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1 and 2 as clock-indices. scpi_clk has 2 output clocks namely: pxlclk0
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and pxlclk1 with 3 and 4 as clock-indices.
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The first consumer in the example is cpu@0 and it has '0' as the clock
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specifier which points to the first entry in the output clocks of
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scpi_dvfs i.e. "atlclk".
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Similarly the second example is hdlcd@7ff60000 and it has pxlclk1 as input
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clock. '4' in the clock specifier here points to the second entry
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in the output clocks of scpi_clocks i.e. "pxlclk1"
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The thermal-sensors property in the soc_thermal node uses the
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temperature sensor provided by SCP firmware to setup a thermal
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zone. The ID "3" is the sensor identifier for the temperature sensor
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as used by the firmware.
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The num-domains property in scpi-power-domains domain specifies that
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SCPI provides 2 power domains. The hdlcd node uses the power domain with
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domain ID 1.
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