feat(linux): s2idle: Document the mode selection logic by DhruvaG2000 · Pull Request #641 · TexasInstruments/processor-sdk-doc

DhruvaG2000 · 2026-03-18T10:29:31Z

Document the mode selection logic using the s2idle flow

kwillis01

It might be good to see if there are other places in the previous parts of the doc that can be updated or that the new info can loop into and consolidate.

kwillis01

Mostly looks good, I think that the QoS Latency Constraints and Mode Selection section needs to be fixed up to flow better and be a little more condensed.

kwillis01 · 2026-04-15T15:38:06Z

Additionally, could you update the RTC + DDR section in pm_am62lx_low_power_modes.rst with the updated commands needed to enter RTC + DDR? Then you can point to this page from there if the user wants an indepth explanation on s2idle

github-actions · 2026-04-21T10:48:54Z

New warnings found with rstcheck:

source/linux/Foundational_Components/Power_Management/pm_psci_s2idle.rst:537: (ERROR/3) Content block expected for the "note" directive; none found.
source/linux/Foundational_Components/Power_Management/pm_psci_s2idle.rst:538: (WARNING/2) Explicit markup ends without a blank line; unexpected unindent.

github-actions · 2026-04-22T06:14:28Z

New warnings found with rstcheck:

source/linux/Foundational_Components/Power_Management/pm_psci_s2idle.rst:505: (ERROR/3) Content block expected for the "note" directive; none found.
source/linux/Foundational_Components/Power_Management/pm_psci_s2idle.rst:506: (WARNING/2) Explicit markup ends without a blank line; unexpected unindent.

Document the mode selection logic using the s2idle flow Signed-off-by: Dhruva Gole <d-gole@ti.com>

Add mention of the s2idle based mode selection being part of low power mode support as of this release Signed-off-by: Dhruva Gole <d-gole@ti.com>

kwillis01

It might be good to put explicit instructions on how to enter RTC + DDR via s2idle (besides the constraint setting) in pm_am62lx_low_power_modes. It would give users a quick way to grab the instructions and go.

kwillis01 · 2026-04-24T14:49:16Z

+   If regular [mem] interface is selected in `/sys/power/mem_sleep`, the RTC Only + DDR low power mode requires special steps
   to enter. The steps are documented in :ref:`am62l_suspend_workarounds`.

+RTC Only Plus DDR


Why was this moved? The note added should be in the RTC + DDR section not before it.

Why should it be only in the RTC +DDR section? The note applies to low power mode selection in general. I feel it should belong at the top and hence this was done intentionally.

kwillis01 · 2026-04-24T15:23:52Z

+   Please go through the s2idle docs to understand how to select between multiple low power modes.
+   The steps and overall architecture/ sequence diagrams are documented in :ref:`pm_s2idle_psci`.
+   The default mode via s2idle is RTC Only Plus DDR, since it's the deepest.
+   If regular [mem] interface is selected in `/sys/power/mem_sleep`, the RTC Only + DDR low power mode requires special steps


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

kwillis01 · 2026-04-24T15:45:59Z

+3. Only idle states with ``exit-latency-us + entry-latency-us`` ≤ constraint are considered
+4. The deepest eligible state is selected
+
+**Selecting Specific Low-Power Modes:**


Could you make an explicit mention of /dev/cpu_wakeup_latency here? I think it would be confusing to someone reading this section where QoS constraint is set, but which one?

okay will add that

kwillis01 · 2026-04-24T15:48:20Z

+
+Execute this in a subshell to avoid accidentally keeping it open indefinitely.
+
+**How It Sets QoS Constraints:**


The explanation in this section would make more sense under the How QoS Constraints Work section. Explaining this constraint AFTER giving an example with it doesn't make much sense. This explanation would help set the stage for the examples given in this section.

ti-scaria · 2026-04-27T05:58:32Z

+     - ``syscore_suspend/resume()`` **called** (saves critical platform state)
+
+   * - **Driver Suspend**
+     - Same device PM callbacks as deep sleep


Since we can have both deep sleep and RTC+DDR using s2idle, mentioning specifically deep sleep might create confusion

removing this entirely, since it's not a difference

ti-scaria · 2026-04-27T06:00:58Z

-     - **cpuidle**: Uses the standard CPUidle framework. Additionally, each driver is made idle by calling respective runtime suspend hooks.
-     - **suspend_ops**: Uses driver specific suspend operations before ``PSCI_SYSTEM_SUSPEND`` is called.
-       No governors exist to make any decisions.
+.. list-table:: S2Idle vs Deep Sleep Comparison


is this table for the deep(mem) path or deep sleep mode specifically

ti-scaria · 2026-04-27T06:04:48Z

+     For complete Device Tree definitions including all latency parameters, refer to the platform's
+     device tree source files (e.g., ``k3-am62l3-evm-idle-states.dtso``).
+
+Understanding the Suspend Parameters


The 2 parameters could be clubbed together, since most of the information is repeated other than the State-ID

ti-scaria · 2026-04-27T06:07:57Z

+
+.. code-block:: bash
+
+   exec 4<>/dev/cpu_wakeup_latency; echo 0x3e8 >&4


Might want to keep the value same as in the above example

cshilwant · 2026-04-30T21:07:38Z

@DhruvaG2000 can you re-spin after checking comments from @kwillis01 @ti-scaria

github-actions Bot assigned devarsht, DhruvaG2000, gehariprasath, praneethbajjuri, r-vignesh, uditkumarti and vishalmti Mar 18, 2026

kwillis01 suggested changes Mar 18, 2026

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ti-scaria reviewed Mar 20, 2026

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DhruvaG2000 force-pushed the s2idle_mode_sel_v1 branch from 995b85e to 6209735 Compare March 31, 2026 17:26

github-actions Bot requested review from devarsht, gehariprasath, praneethbajjuri, r-vignesh, uditkumarti and vishalmti March 31, 2026 17:27

kwillis01 suggested changes Apr 1, 2026

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DhruvaG2000 force-pushed the s2idle_mode_sel_v1 branch from 6209735 to 8532d2e Compare April 21, 2026 10:48

github-actions Bot assigned kwillis01 Apr 21, 2026

StaticRocket requested changes Apr 21, 2026

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Comment thread source/linux/Foundational_Components/Power_Management/pm_psci_s2idle.rst Outdated

Comment thread source/linux/Foundational_Components/Power_Management/pm_psci_s2idle.rst

Comment thread source/linux/Foundational_Components/Power_Management/pm_psci_s2idle.rst

DhruvaG2000 force-pushed the s2idle_mode_sel_v1 branch from 8532d2e to 27dc856 Compare April 22, 2026 06:13

DhruvaG2000 added 2 commits April 23, 2026 15:14

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

e8cf43f

Document the mode selection logic using the s2idle flow Signed-off-by: Dhruva Gole <d-gole@ti.com>

feat(pm_am62lx_low_power_modes): mention s2idle approach

f4ad757

Add mention of the s2idle based mode selection being part of low power mode support as of this release Signed-off-by: Dhruva Gole <d-gole@ti.com>

DhruvaG2000 force-pushed the s2idle_mode_sel_v1 branch from 3de7535 to f4ad757 Compare April 24, 2026 12:23

DhruvaG2000 changed the title ~~[RFC] feat(linux): s2idle: Document the mode selection logic~~ feat(linux): s2idle: Document the mode selection logic Apr 24, 2026

DhruvaG2000 marked this pull request as ready for review April 24, 2026 12:39

DhruvaG2000 requested a review from cshilwant as a code owner April 24, 2026 12:39

DhruvaG2000 requested review from VeeruPrudhvi and jeevantelukula as code owners April 24, 2026 12:39

kwillis01 suggested changes Apr 24, 2026

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ti-scaria reviewed Apr 27, 2026

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		Execute this in a subshell to avoid accidentally keeping it open indefinitely.

		How It Sets QoS Constraints:


		.. code-block:: bash

		exec 4<>/dev/cpu_wakeup_latency; echo 0x3e8 >&4

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kwillis01 commented Apr 15, 2026

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cshilwant commented Apr 30, 2026

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