[PATCH] arm64: versal-net: Add retention state for cpu idle

[Jay Buddhabhatti]

Remove the sleep state and replace it with a retention state for CPU idle.
The sleep state powers down the CPU core, and the wake-up time cannot be
guaranteed because the firmware may be busy handling other tasks at the time
of the wake-up request. This leads to unpredictable and potentially high
wake-up latency during CPU idle.

Replace the sleep state with a retention state to avoid this dependency on
firmware. The retention state uses a PSCI suspend parameter of 0: the
core simply executes WFI and retains its context without being powered off.
Since wake-up from WFI is handled entirely in hardware, it is effectively
immediate (a few cycles) and does not depend on firmware availability.

As the core is not powered down, the local timer is retained and
"local-timer-stop" is dropped. The entry/exit latency and min-residency
are set to the nominal minimum (1 us), allowing the cpuidle governor to
select the state even for very short idle windows.

Signed-off-by: Jay Buddhabhatti <jay.buddhabhatti@xxxxxxx>
---
 arch/arm64/boot/dts/xilinx/versal-net.dtsi | 43 +++++++++++-----------
 1 file changed, 21 insertions(+), 22 deletions(-)

diff --git a/arch/arm64/boot/dts/xilinx/versal-net.dtsi b/arch/arm64/boot/dts/xilinx/versal-net.dtsi
index 15f767608e67..792bed588ae1 100644
--- a/arch/arm64/boot/dts/xilinx/versal-net.dtsi
+++ b/arch/arm64/boot/dts/xilinx/versal-net.dtsi
@@ -103,7 +103,7 @@ cpu0: cpu@0 {
 			enable-method = "psci";
 			reg = <0>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -133,7 +133,7 @@ cpu100: cpu@100 {
 			enable-method = "psci";
 			reg = <0x100>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -163,7 +163,7 @@ cpu200: cpu@200 {
 			enable-method = "psci";
 			reg = <0x200>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -193,7 +193,7 @@ cpu300: cpu@300 {
 			enable-method = "psci";
 			reg = <0x300>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -223,7 +223,7 @@ cpu10000: cpu@10000 {
 			enable-method = "psci";
 			reg = <0x10000>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -253,7 +253,7 @@ cpu10100: cpu@10100 {
 			enable-method = "psci";
 			reg = <0x10100>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -283,7 +283,7 @@ cpu10200: cpu@10200 {
 			enable-method = "psci";
 			reg = <0x10200>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -313,7 +313,7 @@ cpu10300: cpu@10300 {
 			enable-method = "psci";
 			reg = <0x10300>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -343,7 +343,7 @@ cpu20000: cpu@20000 {
 			enable-method = "psci";
 			reg = <0x20000>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -373,7 +373,7 @@ cpu20100: cpu@20100 {
 			enable-method = "psci";
 			reg = <0x20100>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -403,7 +403,7 @@ cpu20200: cpu@20200 {
 			enable-method = "psci";
 			reg = <0x20200>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -433,7 +433,7 @@ cpu20300: cpu@20300 {
 			enable-method = "psci";
 			reg = <0x20300>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -463,7 +463,7 @@ cpu30000: cpu@30000 {
 			enable-method = "psci";
 			reg = <0x30000>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -493,7 +493,7 @@ cpu30100: cpu@30100 {
 			enable-method = "psci";
 			reg = <0x30100>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -523,7 +523,7 @@ cpu30200: cpu@30200 {
 			enable-method = "psci";
 			reg = <0x30200>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -553,7 +553,7 @@ cpu30300: cpu@30300 {
 			enable-method = "psci";
 			reg = <0x30300>;
 			operating-points-v2 = <&cpu_opp_table>;
-			cpu-idle-states = <&CPU_SLEEP_0>;
+			cpu-idle-states = <&CPU_RETENTION_0>;
 			d-cache-size = <0x10000>; /* 64kB */
 			d-cache-line-size = <64>;
 			/* 4 ways set associativity */
@@ -636,13 +636,12 @@ llc: l4-cache { /* LLC inside CMN */
 		idle-states {
 			entry-method = "psci";
 
-			CPU_SLEEP_0: cpu-sleep-0 {
+			CPU_RETENTION_0: cpu-retention-0 {
 				compatible = "arm,idle-state";
-				arm,psci-suspend-param = <0x40000000>;
-				local-timer-stop;
-				entry-latency-us = <300>;
-				exit-latency-us = <600>;
-				min-residency-us = <10000>;
+				arm,psci-suspend-param = <0>;
+				entry-latency-us = <1>;
+				exit-latency-us = <1>;
+				min-residency-us = <1>;
 			};
 		};
 	};
-- 
2.34.1