[PATCH v2] arm64: dts: ti: k3-j721e: Add support for DFS in J721E A72

[Neha Malcom Francis]

Add 2G, 1G, 500M and 250M as the supported frequencies for A72. This
enables support for Dynamic Frequency Scaling (DFS). Note that Dynamic
Voltage and Frequency Scaling (DVFS) is not supported on J7 devices.

J721E SoC has three different speed grade devices (see [1], 7.5
Operating Performance Points) which as of today are indiscernible in
software, users of a different speed grade device must manually change
the DTS to ensure their maximum speed frequency is supported.

To obtain clock-latency-ns, the maximum time was found to switch from/to
any frequency for a CPU and this value was rounded off and set.

[1] https://www.ti.com/lit/gpn/tda4vm

Signed-off-by: Neha Malcom Francis <n-francis at ti.com>
---
Test and boot logs:
https://gist.github.com/nehamalcom/33608837ab5ad3332ff11a7fa7a602e2

Changes since v1:
https://lore.kernel.org/all/20231214075637.176586-1-n-francis@ti.com/
- removed OPPs 1.5G and 750M as they introduced boot regression in
  J721E-SK
- Nishanth
	- indicated DVFS not supported in commit message
	- moved critical data sheet info from below tear line to commit
	  message
	- added opp-shared property
	- added clock-latency-ns property

 arch/arm64/boot/dts/ti/k3-j721e.dtsi | 31 ++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/arch/arm64/boot/dts/ti/k3-j721e.dtsi b/arch/arm64/boot/dts/ti/k3-j721e.dtsi
index a200810df54a..5de6c70bd989 100644
--- a/arch/arm64/boot/dts/ti/k3-j721e.dtsi
+++ b/arch/arm64/boot/dts/ti/k3-j721e.dtsi
@@ -48,6 +48,9 @@ cpu0: cpu at 0 {
 			d-cache-line-size = <64>;
 			d-cache-sets = <256>;
 			next-level-cache = <&L2_0>;
+			clocks = <&k3_clks 202 2>;
+			clock-names = "cpu";
+			operating-points-v2 = <&cpu0_opp_table>;
 		};
 
 		cpu1: cpu at 1 {
@@ -62,6 +65,34 @@ cpu1: cpu at 1 {
 			d-cache-line-size = <64>;
 			d-cache-sets = <256>;
 			next-level-cache = <&L2_0>;
+			clocks = <&k3_clks 203 0>;
+			clock-names = "cpu";
+			operating-points-v2 = <&cpu0_opp_table>;
+		};
+	};
+
+	cpu0_opp_table: opp-table {
+		compatible = "operating-points-v2";
+		opp-shared;
+
+		opp6-2000000000 {
+			opp-hz = /bits/ 64 <2000000000>;
+			clock-latency-ns = <300000>;
+		};
+
+		opp4-1000000000 {
+			opp-hz = /bits/ 64 <1000000000>;
+			clock-latency-ns = <300000>;
+		};
+
+		opp2-500000000 {
+			opp-hz = /bits/ 64 <500000000>;
+			clock-latency-ns = <300000>;
+		};
+
+		opp1-250000000 {
+			opp-hz = /bits/ 64 <250000000>;
+			clock-latency-ns = <300000>;
 		};
 	};
 
-- 
2.34.1