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.

StaticRocket · 2026-04-21T22:54:02Z

+       printf("QoS set to %s. Press Ctrl+C to exit.\n", LATENCY_VAL);
+
+       while (keep_running)
+           sleep(1);
+
+       close(fd);
+       printf("Released.\n");
+       return 0;


Why are we holding this process open with an aggressive loop? There's nothing in the kernel docs that says the value is dropped when the FD is released.

@StaticRocket kernel source code is the kernel documentation ;)
See kernel/power/qos.c: file_operations cpu_wakeup_latency_qos_fops --> cpu_wakeup_latency_qos_release

In that case, why not use pause instead of locking a thread at 100% or sleeping an arbitrary amount of time?

Actually you already setup part of your signal handler. Might as well go all the way.
https://sourceware.org/glibc/manual/latest/html_mono/libc.html#Sigsuspend

@StaticRocket Can we revisit this improvement in future? Right now the focus was on the rest of the docs introducing s2idle based mode selection. How we do it can always be in multiple ways.
However I completely appreciate the input, I need to read up a bit on sigsuspend to understand it's benefit.

Sure. Just seen too many people take the examples at face value.

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.

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?

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.

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

		How It Sets QoS Constraints:

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