fix(asusd): re-apply fan curves after every platform profile write

[ElXreno]

Description

I went digging into why my custom fan curves kept quietly reverting to the factory curve, and it turns out that any write to the platform profile makes the kernel disable all of them. fan_curve_enable_store() in asus-wmi.c takes the disable path into throttle_thermal_policy_write(), which clears enabled on every fan curve device at once. That is what the "the kernel currently resets all if one is" comment over in rog-profiles is talking about. asusd only re-applies the curves in the AC/DC handler and in the platform profile watcher, so every other profile write leaves them disabled while the config still reports them as enabled.

The practical result is that the curves get dropped on every daemon start. start_tasks() calls CtrlPlatform::reload(), which calls update_policy_ac_or_bat() and writes the profile a couple of milliseconds after CtrlFanCurveZbus::reload() had just enabled them. Nothing puts them back afterwards, and since asusd set the profile itself there is no change event for the watcher to pick up. Here is an unpatched start on 6.4.0, timestamps trimmed to the fractional part:

.336844  write_profile_curve_to_platform  CPU
.337258  write_profile_curve_to_platform  GPU
.337681  FanCurves: initialized
.339480  CtrlPlatform: initialized
.342134  ThrottlePolicy setting EPP
.346891  CtrlPlatform: tasks started

Note the empty gap between the policy write and tasks started. After that pwm1_enable and pwm2_enable both read 2, the EC is back on its factory curve, and asusctl fan-curve --mod-profile performance still cheerfully reports enabled: true. One detail that cost me a while during debugging: the curve point read-back keeps showing the custom curve because that is the driver's cached copy, so pwm*_enable is the only thing worth trusting there.

enable_ppt_group() runs into the same problem from a different direction. It rewrites the same profile value on purpose so that ACPI resets PPT to defaults, which disables the curves, and because the value did not actually change there is nothing for the watcher to notice either.

There are four set_platform_profile() call sites in ctrl_platform.rs and only one of them was paired with a re-apply, so rather than adding a fourth pairing I pulled the curve half of apply_fan_curves_and_ppt() out into reapply_fan_curves() and added write_platform_profile(), which writes the profile and then restores the curves. All four sites go through it now, which leaves exactly one direct self.platform.set_platform_profile() call in the file and makes the invariant harder to lose by accident later.

I deliberately left the existing apply_fan_curves_and_ppt() calls alone, even though two of them now end up writing the curve twice in a row. That bundle carries the ordering constraint described in its own doc comment, since PPT writes need Manual fan mode and a curve write is what establishes it, and update_policy_ac_or_bat() can return early without writing anything at all when change_platform_profile_on_ac or _on_battery is false, which would leave a bare PPT write with no curve write ahead of it. The watcher call is not duplication in the first place: it covers profile writes made by other processes such as power-profiles-daemon or a desktop power applet, which asusd has no way to intercept.

#136 and #196 look like the same behaviour seen from the user side, and both were closed as duplicates of #162, which may well be hitting this too. No Fixes line since I cannot test that hardware.

Tested Hardware & Environment

• ASUS Laptop Model: TUF Gaming A15 FA507UV
• Linux Distribution: NixOS unstable
• Kernel Version: 7.1.8-xanmod1

Verification and testing:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My code follows the style guidelines of this project (cargo fmt --all -- --check)
• My changes generate no new warnings (cargo clippy --all -- -D warnings/cargo check --all-targets)
• New and existing unit tests pass locally with my changes (cargo test --all)
• Cranky with 0 warning (cargo cranky)

[coderabbitai]

📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes
  • Improved consistency when switching performance profiles by ensuring custom fan curves are reapplied.
  • Fan-curve settings now remain active across AC/battery profile changes, profile updates, and PPT disablement.

Walkthrough

Platform profile writes now use one centralized path. The path reapplies custom fan curves after kernel profile writes. AC/battery updates, D-Bus profile changes, and PPT disablement use this path.

Changes

Platform profile fan-curve restoration

Layer / File(s)	Summary
Centralized profile write path asusd/src/ctrl_platform.rs	Adds reapply_fan_curves and write_platform_profile. The centralized writer reapplies custom fan curves after a successful kernel write.
Profile update integration asusd/src/ctrl_platform.rs	Routes AC/battery updates, D-Bus profile changes, and PPT disablement through the centralized writer. Existing error handling remains in place.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: 🟡 Moderate · up to 3ff14

Platform profile changes can still report success while custom fan curves remain disabled when restoration fails, leaving users with ineffective fan settings and an inaccurate enabled state. This bounded correctness issue should be addressed before merging.

Suggested labels: asusd, rog-profiles, fix

Suggested reviewers: neroreflex, ghoul4500, luytan

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely states that fan curves are re-applied after every platform profile write.
Description check	✅ Passed	The description provides detailed context, implementation details, tested hardware, environment, verification results, and testing status.

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[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In `@asusd/src/ctrl_platform.rs`:
- Around line 198-200: Update write_platform_profile and reapply_fan_curves to
propagate node-lookup and curve-write failures instead of discarding them, so
D-Bus setters report failure when custom fan curves cannot be restored after
set_platform_profile. Ensure fc.current reflects only the curve state actually
applied.

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• asusd/src/ctrl_platform.rs

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[scardracs]

Ok so, my comment about missing .requires_fan_curve = true, is not totally true anymore, as this value will be dropped as deprecated in the future (we can expect that almost every asus laptops have at least one fan so it's not that useful having a line that specifically says the fan is present when you can simply assume it is). Also, I found later that Armory Crate, for these models, doesn't provide much informations (only PL1/PL2 min/max) like in almost every old intel platforms so don't be bothered by the comments I left under #162

[ElXreno]

#136 is on 6.3.8, so it already has d47b2ea and still shows the boot desync this PR fixes. #162 predates that commit (6.3.7) and was likely fixed by it, so #136 does not look like a duplicate of it.

[scardracs]

#162 was decided to remain as open issue because it contains more infos compared to #136. The problem still remains even with d47b2ea applied so indeed they fall in the same family issues, hence the one with fewer infos will be closed as duplicate

[Ghoul4500]

Thank you for your contribution!