Device Tree Configuration

The device tree file for the JH7110 EVB is located at: kernel/linux/arch/riscv/boot/dts/starfive/jh7110.dtsi. The following sections describe each node and its key parameters.

Thermal Sensor (sfctemp)

The sfctemp node defines the on-chip temperature sensor hardware.

sfctemp: tmon@120e0000  {
            compatible = "starfive,jh7110-temp";
            reg = <0x0 0x120e0000 0x0 0x10000>;
            interrupts = <81>;
            clocks = <&clkgen JH7110_TEMP_SENSOR_CLK_TEMP>,
                 <&clkgen JH7110_TEMP_SENSOR_CLK_APB>;
            clock-names = "sense", "bus";
            resets = <&rstgen RSTN_U0_TEMP_SENSOR_TEMP>,
                 <&rstgen RSTN_U0_TEMP_SENSOR_APB>;
            reset-names = "sense", "bus";
            #thermal-sensor-cells = <0>;
            status = "disabled";
Table 1. sfctemp Parameters
Parameter Description
compatible Compatibility information, used to associate the driver and its target device
reg Sensor register base address and size
interrupts Hardware interrupt number for temperature alerts
clocks Clocks used by the thermal module
clock-names Names of the clocks
resets Rest signals for the thermla module
reset-names Names of the reset signals
thermal-sensor-cells Set to <0> — this sensor provides a single temperature reading with no additional parameters. Referenced by the thermal zone via <&sfctemp>.
status Set to okay to enable the sensor, or disabled to disable it.

CPU as Cooling Device

Each CPU core is declared as a cooling device by adding the #cooling-cells parameter. When the thermal framework detects an over-temperature condition, it instructs the cpufreq driver to reduce the CPU frequency, which lowers power dissipation and temperature.

Following is the example of the #cooling-cells parameter added to CPU0.
cpu0: cpu@0 {
compatible = "sifive,s7", "riscv";
    device_type = "cpu";
reg = <0>;
riscv,isa = "rv64imac_zba_zbb";
/* ... other CPU properties (cache, MMU, etc.) omitted for clarity ... */
#cooling-cells = <2>;
status = "disabled";
};
Table 2. cooling-cells Parameter
Parameter Description
#cooling-cells Required for any device that acts as a cooling actuator. Set to <2> — the two cells specify the minimum and maximum cooling state that the thermal zone's cooling-maps can request.

CPU OPP Table

The OPP (Operating Performance Points) table defines the available CPU frequency and voltage pairs. The cpufreq driver selects from these entries when scaling the CPU frequency — including during thermal throttling. A lower OPP means lower frequency, lower voltage, and less heat.

cluster0_opp: opp-table-0 {
            compatible = "operating-points-v2";
            opp-shared;
            opp-375000000 {
                    opp-hz = /bits/ 64 <375000000>;
                    opp-microvolt = <800000>;
            };
            opp-500000000 {
                    opp-hz = /bits/ 64 <500000000>;
                    opp-microvolt = <800000>;
            };
            opp-750000000 {
                    opp-hz = /bits/ 64 <750000000>;
                    opp-microvolt = <800000>;
                    opp-suspend;
            };
            opp-1500000000 {
                    opp-hz = /bits/ 64 <1500000000>;
                    opp-microvolt = <1040000>;
            };

            /* CPU opp table for 1.25GHz */
            opp-312500000 {
                    opp-hz = /bits/ 64 <312500000>;
                    opp-microvolt = <800000>;
            };
            opp-417000000 {
                    opp-hz = /bits/ 64 <417000000>;
                    opp-microvolt = <800000>;
            };
            opp-625000000 {
                    opp-hz = /bits/ 64 <625000000>;
                    opp-microvolt = <800000>;
                    opp-suspend;
            };
            opp-1250000000 {
                    opp-hz = /bits/ 64 <1250000000>;
                    opp-microvolt = <1000000>;
            };
    };
Table 3. OPP Table Parameters
Parameter Description
compatible Must be "operating-points-v2" for the OPP v2 binding.
opp-shared Indicates all CPU cores in the cluster share the same OPP (frequency scaling applies to the entire cluster, not individual cores).
opp-hz Target CPU frequency in Hz.
opp-microvolt Required supply voltage in microvolts for this frequency.
opp-suspend Marks this OPP as the preferred frequency during system suspend.

Thermal Zone: Trip Points and Cooling Maps

The thermal-zones node ties the sensor, trip points, and cooling devices into a complete thermal policy. It defines:
  • Which sensor to read (thermal-sensors)
  • When to take action (trips : temperature thresholds)
  • What to do when a threshold is crossed (cooling-maps: which cooling devices to activate)
thermal-zones {
            cpu-thermal {
                polling-delay-passive = <250>;
                polling-delay = <15000>;

                thermal-sensors = <&sfctemp>;

                trips {
                    cpu_alert0: cpu_alert0 {
                        /* milliCelsius */
                        temperature = <85000>;
                        hysteresis = <2000>;
                        type = "passive";
                    };

                    cpu_crit: cpu_crit {
                        /* milliCelsius */
                        temperature = <100000>;
                        hysteresis = <2000>;
                        type = "critical";
                    };
                };

                cooling-maps {
                    map0 {
                        trip = <&cpu_alert0>;
                        cooling-device =
                            <&cpu0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
                            <&cpu1 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
                            <&cpu2 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
                            <&cpu3 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
                    };
                };
            };
        };
Table 4. Thermal Zone Parameters
Parameter Description
cpu-thermal Node
polling-delay-passive Polling interval (ms) when a passive trip is active.
polling-delay Polling interval (ms) when no passive trip is active.
thermal-sensors References the sensor node ( &sfctemp ) that provides temperature readings for this zone.
trips Node
temperature Trip threshold in milli-degrees Celsius.
hysteresis Temperature hysteresis in milli-degrees Celsius.
type passive — the framework activates cooling devices to reduce temperature. critical — the framework performs an emergency shutdown.
cooling-maps Node
trip References the trip point that triggers this cooling action, for example, <&cpu_alert0>.
cooling-device

References one or more cooling devices. Each entry is <&cpuN min_state max_state>. .

HERMAL_NO_LIMIT means the thermal framework can use the full cooling range (from no throttling to maximum throttling).