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feat(linux): s2idle: Document the mode selection logic #641

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feat(linux): s2idle: Document the mode selection logic
DhruvaG2000 Mar 18, 2026
f4ad757
feat(pm_am62lx_low_power_modes): mention s2idle approach
DhruvaG2000 Apr 24, 2026
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60 changes: 25 additions & 35 deletions ...ce/linux/Foundational_Components/Power_Management/pm_am62lx_low_power_modes.rst
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Expand Up @@ -80,14 +80,17 @@
detects that the RTC is already programmed and skips the full initialization, performing only minimal
cleanup to preserve the system time.

RTC Only Plus DDR
*****************

.. note::

For this release, the RTC Only + DDR low power mode requires special steps
Please go through the s2idle docs to understand how to select between multiple low power modes.

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[RedHat.SimpleWords] Use simple language. Consider using 'many' rather than 'multiple'.

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{"message": "[RedHat.SimpleWords] Use simple language. Consider using 'many' rather than 'multiple'.", "location": {"path": "source/linux/Foundational_Components/Power_Management/pm_am62lx_low_power_modes.rst", "range": {"start": {"line": 85, "column": 74}}}, "severity": "INFO"}
The steps and overall architecture/ sequence diagrams are documented in :ref:`pm_s2idle_psci`.

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[RedHat.PassiveVoice] 'are documented' is passive voice. In general, use active voice. Consult the style guide for acceptable use of passive voice.

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{"message": "[RedHat.PassiveVoice] 'are documented' is passive voice. In general, use active voice. Consult the style guide for acceptable use of passive voice.", "location": {"path": "source/linux/Foundational_Components/Power_Management/pm_am62lx_low_power_modes.rst", "range": {"start": {"line": 86, "column": 58}}}, "severity": "INFO"}
The default mode via s2idle is RTC Only Plus DDR, since it's the deepest.

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[RedHat.Contractions] Avoid contractions. Use ''it is'' rather than 'it's.'

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{"message": "[RedHat.Contractions] Avoid contractions. Use ''it is'' rather than 'it's.'", "location": {"path": "source/linux/Foundational_Components/Power_Management/pm_am62lx_low_power_modes.rst", "range": {"start": {"line": 87, "column": 60}}}, "severity": "INFO"}

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[RedHat.Definitions] Define acronyms and abbreviations (such as 'DDR') on first occurrence if they're likely to be unfamiliar.

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{"message": "[RedHat.Definitions] Define acronyms and abbreviations (such as 'DDR') on first occurrence if they're likely to be unfamiliar.", "location": {"path": "source/linux/Foundational_Components/Power_Management/pm_am62lx_low_power_modes.rst", "range": {"start": {"line": 87, "column": 49}}}, "severity": "INFO"}

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[RedHat.Definitions] Define acronyms and abbreviations (such as 'RTC') on first occurrence if they're likely to be unfamiliar.

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{"message": "[RedHat.Definitions] Define acronyms and abbreviations (such as 'RTC') on first occurrence if they're likely to be unfamiliar.", "location": {"path": "source/linux/Foundational_Components/Power_Management/pm_am62lx_low_power_modes.rst", "range": {"start": {"line": 87, "column": 35}}}, "severity": "INFO"}

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[RedHat.TermsSuggestions] Depending on the context, consider using 'through', 'by', 'from', 'on', or 'by using' rather than 'via'.

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{"message": "[RedHat.TermsSuggestions] Depending on the context, consider using 'through', 'by', 'from', 'on', or 'by using' rather than 'via'.", "location": {"path": "source/linux/Foundational_Components/Power_Management/pm_am62lx_low_power_modes.rst", "range": {"start": {"line": 87, "column": 21}}}, "severity": "INFO"}
If regular [mem] interface is selected in `/sys/power/mem_sleep`, the RTC Only + DDR low power mode requires special steps

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[RedHat.Definitions] Define acronyms and abbreviations (such as 'DDR') on first occurrence if they're likely to be unfamiliar.

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{"message": "[RedHat.Definitions] Define acronyms and abbreviations (such as 'DDR') on first occurrence if they're likely to be unfamiliar.", "location": {"path": "source/linux/Foundational_Components/Power_Management/pm_am62lx_low_power_modes.rst", "range": {"start": {"line": 88, "column": 85}}}, "severity": "INFO"}

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[RedHat.Definitions] Define acronyms and abbreviations (such as 'RTC') on first occurrence if they're likely to be unfamiliar.

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{"message": "[RedHat.Definitions] Define acronyms and abbreviations (such as 'RTC') on first occurrence if they're likely to be unfamiliar.", "location": {"path": "source/linux/Foundational_Components/Power_Management/pm_am62lx_low_power_modes.rst", "range": {"start": {"line": 88, "column": 74}}}, "severity": "INFO"}

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[RedHat.PassiveVoice] 'is selected' is passive voice. In general, use active voice. Consult the style guide for acceptable use of passive voice.

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{"message": "[RedHat.PassiveVoice] 'is selected' is passive voice. In general, use active voice. Consult the style guide for acceptable use of passive voice.", "location": {"path": "source/linux/Foundational_Components/Power_Management/pm_am62lx_low_power_modes.rst", "range": {"start": {"line": 88, "column": 31}}}, "severity": "INFO"}
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@kwillis01 kwillis01 Apr 24, 2026

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Are we supporting users to use the work around as well as s2idle?

to enter. The steps are documented in :ref:`am62l_suspend_workarounds`.

RTC Only Plus DDR

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{"message": "[RedHat.Definitions] Define acronyms and abbreviations (such as 'RTC') on first occurrence if they're likely to be unfamiliar.", "location": {"path": "source/linux/Foundational_Components/Power_Management/pm_am62lx_low_power_modes.rst", "range": {"start": {"line": 91, "column": 1}}}, "severity": "INFO"}
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Why was this moved? The note added should be in the RTC + DDR section not before it.

*****************

RTC Only + DDR mode is the deepest low power mode that allows the system to enter a state of lowest power consumption
while still retaining the DDR RAM context.

Expand All @@ -108,37 +111,24 @@

.. code-block:: console

root@am62lxx-evm:~# echo mem > /sys/power/state
[ 67.335138] PM: suspend entry (deep)
[ 67.358190] Filesystems sync: 0.019 seconds
[ 67.363206] Freezing user space processes
[ 67.368991] Freezing user space processes completed (elapsed 0.001 seconds)
[ 67.376038] OOM killer disabled.
[ 67.379271] Freezing remaining freezable tasks
[ 67.384973] Freezing remaining freezable tasks completed (elapsed 0.001 seconds)
[ 67.392398] printk: Suspending console(s) (use no_console_suspend to debug)
NOTICE: bl1_plat_arch_setup arch setup
NOTICE: Booting Trusted Firmware
NOTICE: BL1: v2.12.0(release):11.00.04-7-gaa3963759-dirty
NOTICE: BL1: Built : 15:56:37, Feb 25 2025
NOTICE: lpdd4_init <--
NOTICE: DDR ram size =80000000
NOTICE: bl1_platform_setup DDR init done
NOTICE: k3_bl1_handoff sent message to tifs
ERROR: Wake up src 0x0
ERROR: Wake up interrupt 0xc
[ 67.405953] Disabling non-boot CPUs ...
[ 67.408032] psci: CPU1 killed (polled 0 ms)
[ 67.408974] Enabling non-boot CPUs ...
[ 67.409281] Detected VIPT I-cache on CPU1
[ 67.409330] GICv3: CPU1: found redistributor 1 region 0:0x0000000001860000
[ 67.409393] CPU1: Booted secondary processor 0x0000000001 [0x410fd034]
[ 67.410371] CPU1 is up
[ 67.446329] OOM killer enabled.
[ 67.449479] Restarting tasks ... done.
[ 67.454324] random: crng reseeded on system resumption
[ 67.459689] PM: suspend exit

root@am62lxx-evm:~# rtcwake -s 5 -m mem
rtcwake: assuming RTC uses UTC ...
rtcwake: wakeup from "mem" using /dev/rtc0 at Thu Jan 1 00:04:20 1970
[ 222.269447] PM: suspend entry (s2idle)
[ 222.273481] Filesystems sync: 0.000 seconds
[ 222.281882] Freezing user space processes
[ 222.291800] Freezing user space processes completed (elapsed 0.002 seconds)
[ 222.298873] OOM killer disabled.
[ 222.302177] Freezing remaining freezable tasks
[ 222.308071] Freezing remaining freezable tasks completed (elapsed 0.001 seconds)
[ 222.349890] xhci-hcd xhci-hcd.1.auto: xHC error in resume, USBSTS 0x401, Reinit
[ 222.357227] usb usb1: root hub lost power or was reset
[ 222.362980] xhci-hcd xhci-hcd.1.auto: USB3 root hub has no ports
[ 222.395078] OOM killer enabled.
[ 222.398356] Restarting tasks: Starting
[ 222.419490] Restarting tasks: Done
[ 222.430220] random: crng reseeded on system resumption
[ 222.445468] PM: suspend exit

DeepSleep
*********
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