nvidia-drm: Skip empty atomic commit in nv_drm_revoke_modeset_permission

[Himesh-Kundal]

Description

When any process holding an open DRM file descriptor closes it (such as client utilities, browsers, or Wayland sub-processes), nv_drm_revoke_modeset_permission() is called to revoke modeset permissions and disable associated connectors.

In the current implementation, if the closing file descriptor did not hold modesetting permissions on any connector, drm_atomic_commit(state) is still unconditionally called with an empty atomic state transaction.

Submitting an empty atomic commit:

1. Incurs unnecessary hardware and modeset lock contention with active page flips and compositors.
2. Triggers redundant DRM atomic check/commit pipeline execution.

Proposed Change

Introduce a flag (need_commit) during the connector iteration. Only invoke drm_atomic_commit(state) if at least one connector was actually modified/revoked. If no connector state was altered, the allocated state is simply freed via nv_drm_atomic_state_base_put(state).

This mirrors the existing conditional commit pattern used in nv_drm_plane_reset_input_colorspace() in the same file and follows NVIDIA's convention of using braces around single-statement control blocks in this driver.

Testing & Validation

Tested on a hybrid Intel UHD + NVIDIA GeForce RTX 4050 Mobile system driving an external 1440p display over direct HDMI under Wayland (Hyprland / Aquamarine):

1. Non-modeset client teardown (need_commit == false):

   • Repeatedly opened and closed DRM file handles from non-modeset clients (monitoring utilities, hardware-accelerated browsers, and Vulkan compute clients).
   • Confirmed that nv_drm_revoke_modeset_permission() exits without submitting an empty atomic commit, freeing state cleanly with zero lock contention on active compositor page flips.

2. Legitimate modeset revocation (need_commit == true):

   • Executed VT switches (chvt 1 / chvt 2) and compositor exits where DRM master permissions are actively relinquished.
   • Confirmed nv_drm_atomic_disable_connector() sets need_commit = true, and drm_atomic_commit(state) executes normally without regressions or connector state leaks.

3. Selective revocation (dpyId != 0):

   • Verified that selective display revocation only marks need_commit = true when the specific display ID matches the closing file descriptor.

[CLAassistant]

All committers have signed the CLA.