[PATCH v2 11/11] arm64: dts: rockchip: rk3588: add passive cooling to the NPU thermal zone

[Igor Paunovic <royalnet026@gmail.com>]

The NPU zone has had only a critical trip at 115 degrees, which is a
shutdown and not a cooling policy. Now that the NPU can be throttled by
capping its clock, give the zone a passive trip and a cooling map, in the
same shape and at the same temperatures as the GPU zone right above it:
85 degrees with 2 degrees of hysteresis, and a 100 ms passive polling
delay.

The #cooling-cells property goes on rknn_core_0, the first of the three
core nodes, as the one node that stands for the shared clock as a cooling
device. The other two cores have no clock of their own and cannot be
throttled independently of it.

The cooling map is inert until the driver registers a cooling device:
thermal_of_should_bind() only resolves a map entry once a matching cdev
appears, so this patch on its own changes nothing but the trip point. On a
board that leaves the NPU disabled the passive trip has no cooling device
to act on and only changes the polling rate above 85 degrees, as the GPU
zone's trip already does on a board without the GPU.

The thermal path itself has not been exercised on the board this was
written on. Reaching 85 degrees on an NPU workload with the fan curve here
has not been possible, so what is verified is that the zone parses and
binds, not that throttling engages at temperature.

Assisted-by: LLM checkpatch dtbs_check
Signed-off-by: Igor Paunovic <royalnet026@gmail.com>
---
v2: commit message only: wording for the shared table, and a sentence
on boards that leave the NPU disabled. The diff is unchanged.

 arch/arm64/boot/dts/rockchip/rk3588-base.dtsi | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/boot/dts/rockchip/rk3588-base.dtsi b/arch/arm64/boot/dts/rockchip/rk3588-base.dtsi
index 376ad04e07869..c3d22b08f415b 100644
--- a/arch/arm64/boot/dts/rockchip/rk3588-base.dtsi
+++ b/arch/arm64/boot/dts/rockchip/rk3588-base.dtsi
@@ -1162,6 +1162,7 @@ rknn_core_0: npu@fdab0000 {
 		clock-names = "aclk", "hclk", "npu", "pclk";
 		assigned-clocks = <&scmi_clk SCMI_CLK_NPU>;
 		assigned-clock-rates = <200000000>;
+		#cooling-cells = <2>;
 		resets = <&cru SRST_A_RKNN0>, <&cru SRST_H_RKNN0>;
 		reset-names = "srst_a", "srst_h";
 		power-domains = <&power RK3588_PD_NPUTOP>;
@@ -3212,17 +3213,31 @@ map0 {
 		};
 
 		npu_thermal: npu-thermal {
-			polling-delay-passive = <0>;
+			polling-delay-passive = <100>;
 			polling-delay = <0>;
 			thermal-sensors = <&tsadc 6>;
 
 			trips {
+				npu_alert: npu-alert {
+					temperature = <85000>;
+					hysteresis = <2000>;
+					type = "passive";
+				};
+
 				npu_crit: npu-crit {
 					temperature = <115000>;
 					hysteresis = <0>;
 					type = "critical";
 				};
 			};
+
+			cooling-maps {
+				map0 {
+					trip = <&npu_alert>;
+					cooling-device =
+						<&rknn_core_0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
+				};
+			};
 		};
 	};
 
-- 
2.43.0