From: Michal Simek <michal.simek@amd.com>
To: Jay Buddhabhatti <jay.buddhabhatti@amd.com>,
robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org
Cc: devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, git@amd.com
Subject: Re: [PATCH] arm64: versal-net: Add retention state for cpu idle
Date: Tue, 11 Aug 2026 09:23:05 +0200 [thread overview]
Message-ID: <48dc79b5-8120-4cb2-9c58-657ef3959e27@amd.com> (raw)
In-Reply-To: <20260727121842.3410495-1-jay.buddhabhatti@amd.com>
On 7/27/26 14:18, Jay Buddhabhatti wrote:
> 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@amd.com>
> ---
> 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>;
> };
> };
> };
This patch should likely changed because default cpuidle-psci creates wfi
backend automatically when no DT idle states are detected. Jay is looking into it.
Thanks,
Michal
prev parent reply other threads:[~2026-08-11 7:23 UTC|newest]
Thread overview: 3+ 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 [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=48dc79b5-8120-4cb2-9c58-657ef3959e27@amd.com \
--to=michal.simek@amd.com \
--cc=conor+dt@kernel.org \
--cc=devicetree@vger.kernel.org \
--cc=git@amd.com \
--cc=jay.buddhabhatti@amd.com \
--cc=krzk+dt@kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=robh@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox