From: Prasanna Kumar T S M <ptsm@linux.microsoft.com>
To: Jay Buddhabhatti <jay.buddhabhatti@amd.com>,
git@amd.com, ptsm@microsoft.com, robh@kernel.org,
krzk+dt@kernel.org, conor+dt@kernel.org, michal.simek@amd.com,
sven@kernel.org
Cc: devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] arm64: dts: xilinx: versal-net: Remove CPU idle states
Date: Thu, 15 Oct 2026 15:01:01 +0530 [thread overview]
Message-ID: <20175a31-2ef8-4c12-b329-616cb07d3d0b@linux.microsoft.com> (raw)
In-Reply-To: <b9213a36eb1d28f3e7b8610592c085f627f5c7cf.1791374721.git.jay.buddhabhatti@amd.com>
On 07-10-2026 17:49, Jay Buddhabhatti wrote:
> 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.
>
> Remove the sleep state to avoid this dependency on firmware. The default
> backend CPU idle state simply puts core in 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.
>
> Signed-off-by: Jay Buddhabhatti <jay.buddhabhatti@amd.com>
> ---
> Changes in v2:
> - Remove the idle state instead of replacing it with a retention state.
> - Update the subject and commit description.
>
> Link to v1: https://lore.kernel.org/all/20260727121842.3410495-1-jay.buddhabhatti@amd.com/
> ---
> arch/arm64/boot/dts/xilinx/versal-net.dtsi | 29 ----------------------
> 1 file changed, 29 deletions(-)
>
> diff --git a/arch/arm64/boot/dts/xilinx/versal-net.dtsi b/arch/arm64/boot/dts/xilinx/versal-net.dtsi
> index 21bb917bcba1..9b74e59fd64a 100644
> --- a/arch/arm64/boot/dts/xilinx/versal-net.dtsi
> +++ b/arch/arm64/boot/dts/xilinx/versal-net.dtsi
> @@ -103,7 +103,6 @@ cpu0: cpu@0 {
> enable-method = "psci";
> reg = <0>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -133,7 +132,6 @@ cpu100: cpu@100 {
> enable-method = "psci";
> reg = <0x100>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -163,7 +161,6 @@ cpu200: cpu@200 {
> enable-method = "psci";
> reg = <0x200>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -193,7 +190,6 @@ cpu300: cpu@300 {
> enable-method = "psci";
> reg = <0x300>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -223,7 +219,6 @@ cpu10000: cpu@10000 {
> enable-method = "psci";
> reg = <0x10000>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -253,7 +248,6 @@ cpu10100: cpu@10100 {
> enable-method = "psci";
> reg = <0x10100>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -283,7 +277,6 @@ cpu10200: cpu@10200 {
> enable-method = "psci";
> reg = <0x10200>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -313,7 +306,6 @@ cpu10300: cpu@10300 {
> enable-method = "psci";
> reg = <0x10300>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -343,7 +335,6 @@ cpu20000: cpu@20000 {
> enable-method = "psci";
> reg = <0x20000>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -373,7 +364,6 @@ cpu20100: cpu@20100 {
> enable-method = "psci";
> reg = <0x20100>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -403,7 +393,6 @@ cpu20200: cpu@20200 {
> enable-method = "psci";
> reg = <0x20200>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -433,7 +422,6 @@ cpu20300: cpu@20300 {
> enable-method = "psci";
> reg = <0x20300>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -463,7 +451,6 @@ cpu30000: cpu@30000 {
> enable-method = "psci";
> reg = <0x30000>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -493,7 +480,6 @@ cpu30100: cpu@30100 {
> enable-method = "psci";
> reg = <0x30100>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -523,7 +509,6 @@ cpu30200: cpu@30200 {
> enable-method = "psci";
> reg = <0x30200>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -553,7 +538,6 @@ cpu30300: cpu@30300 {
> enable-method = "psci";
> reg = <0x30300>;
> operating-points-v2 = <&cpu_opp_table>;
> - cpu-idle-states = <&CPU_SLEEP_0>;
> d-cache-size = <0x10000>; /* 64kB */
> d-cache-line-size = <64>;
> /* 4 ways set associativity */
> @@ -632,19 +616,6 @@ llc: l4-cache { /* LLC inside CMN */
> cache-size = <0x1000000>; /* 16MB */
> cache-unified;
> };
> -
> - idle-states {
> - entry-method = "psci";
> -
> - CPU_SLEEP_0: cpu-sleep-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>;
> - };
> - };
> };
>
> cpu_opp_table: opp-table {
This change works fine.
Tested-by: Prasanna Kumar T S M <ptsm@linux.microsoft.com>
next prev parent reply other threads:[~2026-10-15 9:31 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-27 12:18 [PATCH] arm64: versal-net: Add retention state for cpu idle Jay Buddhabhatti
2026-07-27 12:29 ` sashiko-bot
2026-08-11 7:23 ` Michal Simek
2026-10-07 12:19 ` [PATCH v2] arm64: dts: xilinx: versal-net: Remove CPU idle states Jay Buddhabhatti
2026-10-15 9:31 ` Prasanna Kumar T S M [this message]
2026-10-15 9:51 ` Prasanna Kumar T S M
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