Corrupt vblank timestamps on HDMI 2.1 DSC output (4K@240) — frame scheduling breaks under niri

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评估

难度
5/5
预计耗时
一周以上
新手友好度
30/100
Issue 类型
缺陷
描述清晰度
基本清楚
活跃度
活跃
技术栈
c, linux

调研方向

Start by locating the driver's vblank timestamp generation paths for HDMI 2.1 DSC and non-standard display timings; the issue does not name specific files or tests. Compare reported vblank intervals with the expected refresh intervals for the affected outputs, then check whether the eDP control case remains unaffected. Done means timestamps match the refresh interval and the reported tearing and scheduling warnings no longer occur.

由索引模型根据 Issue 内容生成。

描述

System

  • GPU: RTX 4080 Laptop (open kernel modules 595.104.02)
  • Machine: MSI Vector 16 HX A13VHG
  • OS: NixOS, kernel 6.18.57
  • Compositor: niri 26.04 / niri-unstable-20261022 (both reproduce)

Symptom

On HDMI-A-3 (Microstep MPG272UX OLED, 3840x2160@240, DSC dual-slice), vblank timestamps reported to userspace are wildly incorrect — compositor observes vblank deltas of 1-4ms against an expected 4.166ms interval. Visual result: bottom half of screen shows stale/torn frames (scanline flicker).

Reproduction

  1. Connect 4K OLED via HDMI 2.1 at 240Hz (DSC engaged)
  2. Launch niri → niri::utils::vblank_throttle warnings appear within seconds:
    HDMI-A-3: expected refresh 4.166ms, got vblank after 1.562ms
    DP-4 ([email protected], non-standard timing): expected 8.333ms, got vblank after 2.713ms
    
  3. Drop HDMI-A-3 to [email protected] → warnings stop, picture clean

Notes

  • Same class of corruption on a [email protected] (non-standard CVT timing) DisplayPort output — expected 8.33ms, got 2.7ms.
  • Internal eDP-1 2560x1600@240 never affected.
  • Suspect DSC and/or non-standard timing paths in the driver's vblank timestamp generation.

Cross-filed at niri-wm/niri#4724 for compositor-side handling.

主要语言
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环境准备

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  • 没有 Pull Request 模板
  • 阅读贡献指南

从这里开始

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  2. 在 Issue 下留言说明你要接手 —— 这能避免两个人做同样的事。
  3. Fork 仓库,在一个分支上完成修改。
  4. 提交 Pull Request,并在描述里引用这个 Issue 编号。

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