enable ASYNC_COMMIT on planes

[henkwiedig]

The MR enables rockchip's vendor specific ASYNC_COMMIT on the drm planes.
Should improve latency a bit.

[qodo-free-for-open-source-projects]

PR Summary by Qodo

Add opt-in asynchronous DRM plane commits

✨ Enhancement 🕐 10-20 Minutes

AI Description

• Adds an opt-in CLI flag for lower-latency Rockchip plane updates.
• Enables vendor ASYNC_COMMIT on supported video and OSD planes.
• Preserves compatibility by silently skipping drivers without the property.

Diagram

graph TD
  CLI["CLI option"] --> Flag["Runtime flag"] --> Video["Video modeset"] --> Prepare["Atomic request"] --> Plane[("DRM plane")]
  Flag --> OSD["OSD modeset"] --> Prepare
  Flag --> Restore["Plane restore"] --> Prepare

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High-Level Assessment

The opt-in, capability-probed plane property is the appropriate approach because ASYNC_COMMIT is vendor-specific and may permit tearing. DRM_MODE_ATOMIC_NONBLOCK was reasonably dismissed because it only makes the ioctl return early rather than applying the plane update immediately.

Files changed (4) +47 / -13

Enhancement (4) +47 / -13

drm.cConditionally enable ASYNC_COMMIT during atomic preparation +28/-7

Conditionally enable ASYNC_COMMIT during atomic preparation

• Adds a silent plane-property capability check and sets Rockchip's ASYNC_COMMIT when requested. Propagates the option through initial modesets and plane restoration while retaining compatibility with drivers that lack the property.

src/drm.c

drm.hExpose asynchronous commit parameters in DRM APIs +3/-3

Expose asynchronous commit parameters in DRM APIs

• Extends the modeset, atomic preparation, and plane restoration declarations with an async-commit argument.

src/drm.h

main.cppAdd the asynchronous plane commit CLI option +14/-2

Add the asynchronous plane commit CLI option

• Introduces --async-commit-planes, documents its latency and tearing tradeoff, logs its state, and passes it into video initialization and cleanup restoration.

src/main.cpp

osd.cppApply asynchronous commit selection to OSD setup +2/-1

Apply asynchronous commit selection to OSD setup

• Passes the shared async-commit setting into the OSD plane's initial modeset.

src/osd.cpp

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Code Review by Qodo

🐞 Bugs (3) 📘 Rule violations (0) 📜 Skill insights (0)

1. Async state survives shutdown 🐞 Bug ≡ Correctness

Description

ASYNC_COMMIT is documented as persistent, but shutdown passes async_commit_planes into both
restore commits, reasserting 1 instead of restoring the planes' prior values. After one enabled
run exits, a later default run skips the setter and can therefore keep performing asynchronous,
tearing plane updates despite --async-commit-planes being absent.

Code

src/main.cpp[2019]

+	restore_planes_zpos(drm_fd, output_list, async_commit_planes);

Evidence

The new code itself states that ASYNC_COMMIT is persistent, only writes it when the option is true,
and then passes that same true value through cleanup immediately before destroying the DRM objects
and closing the fd. There is no commit that writes the property back to zero or to its startup
value.

src/drm.c[955-963]
src/drm.c[968-990]
src/main.cpp[2018-2033]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
`ASYNC_COMMIT` is persistent plane state, but cleanup reasserts the enabled value and leaves it active for subsequent DRM users and later runs.

## Issue Context
Capture each selected plane's original `ASYNC_COMMIT` value before changing it. Apply the requested runtime value explicitly and restore the captured values during shutdown rather than passing the runtime enable flag through the z-position restore path.

## Fix Focus Areas
- src/drm.c[955-968]
- src/drm.c[973-990]
- src/main.cpp[2018-2033]
- src/drm.h[135-149]

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

---

2. Async setter failure ignored 🐞 Bug ☼ Reliability

Description

modeset_atomic_prepare_commit() ignores the result of adding ASYNC_COMMIT to the atomic request
and returns success even when that addition fails. Callers then report preparation as successful and
proceed without the requested behavior or encounter a less-specific commit failure.

Code

src/drm.c[R962-963]

+	if (async_commit && drm_object_has_property(plane, "ASYNC_COMMIT"))
+		set_drm_object_property(req, plane, "ASYNC_COMMIT", 1);

Evidence

The wrapper returns the result of drmModeAtomicAddProperty; all required properties in this
preparation routine check for a negative result, while the newly added async setter discards it and
the routine unconditionally returns zero.

src/drm.c[121-139]
src/drm.c[907-942]
src/drm.c[962-965]
src/drm.c[846-866]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
Failure to add `ASYNC_COMMIT` to the atomic request is discarded, so preparation can falsely report success.

## Issue Context
The required setters in the same function return immediately on failure. Preserve the optional behavior for an absent property, but once the property has been found, propagate or clearly handle a failed `set_drm_object_property()` call.

## Fix Focus Areas
- src/drm.c[962-965]

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

---

3. Packaged option documentation missing 🐞 Bug ⚙ Maintainability

Description

The new --async-commit-planes switch is parsed and shown in built-in help but is absent from the
maintained Debian manpage. Users of the packaged manual cannot discover the latency/tearing option
or its vendor-kernel restriction there.

Code

src/main.cpp[R1568-1571]

+	__OnArgument("--async-commit-planes") {
+		async_commit_planes = true;
+		continue;
+	}

Evidence

The parser and built-in help define the new option, while the manpage's option list proceeds
directly from --disable-vsync to --screen-mode-list.

src/main.cpp[1300-1303]
src/main.cpp[1568-1571]
debian/manpage.md[80-90]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
The new command-line option is missing from the packaged Debian manual.

## Issue Context
Mirror the built-in help text, including the Rockchip BSP requirement, silent unsupported-driver behavior, latency benefit, and tearing tradeoff.

## Fix Focus Areas
- debian/manpage.md[80-90]
- src/main.cpp[1300-1303]

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

---

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1. Async state survives shutdown 🐞 Bug ≡ Correctness

ASYNC_COMMIT is documented as persistent, but shutdown passes async_commit_planes into both
restore commits, reasserting 1 instead of restoring the planes' prior values. After one enabled
run exits, a later default run skips the setter and can therefore keep performing asynchronous,
tearing plane updates despite --async-commit-planes being absent.

Agent Prompt

## Issue description
`ASYNC_COMMIT` is persistent plane state, but cleanup reasserts the enabled value and leaves it active for subsequent DRM users and later runs.

## Issue Context
Capture each selected plane's original `ASYNC_COMMIT` value before changing it. Apply the requested runtime value explicitly and restore the captured values during shutdown rather than passing the runtime enable flag through the z-position restore path.

## Fix Focus Areas
- src/drm.c[955-968]
- src/drm.c[973-990]
- src/main.cpp[2018-2033]
- src/drm.h[135-149]

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

[qodo-free-for-open-source-projects]

2. Async setter failure ignored 🐞 Bug ☼ Reliability

modeset_atomic_prepare_commit() ignores the result of adding ASYNC_COMMIT to the atomic request
and returns success even when that addition fails. Callers then report preparation as successful and
proceed without the requested behavior or encounter a less-specific commit failure.

Agent Prompt

## Issue description
Failure to add `ASYNC_COMMIT` to the atomic request is discarded, so preparation can falsely report success.

## Issue Context
The required setters in the same function return immediately on failure. Preserve the optional behavior for an absent property, but once the property has been found, propagate or clearly handle a failed `set_drm_object_property()` call.

## Fix Focus Areas
- src/drm.c[962-965]

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

[qodo-free-for-open-source-projects]

3. Packaged option documentation missing 🐞 Bug ⚙ Maintainability

The new --async-commit-planes switch is parsed and shown in built-in help but is absent from the
maintained Debian manpage. Users of the packaged manual cannot discover the latency/tearing option
or its vendor-kernel restriction there.

Agent Prompt

## Issue description
The new command-line option is missing from the packaged Debian manual.

## Issue Context
Mirror the built-in help text, including the Rockchip BSP requirement, silent unsupported-driver behavior, latency benefit, and tearing tradeoff.

## Fix Focus Areas
- debian/manpage.md[80-90]
- src/main.cpp[1300-1303]

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools