Re: [PATCH] drm/connector: add CRTC state change callback to HDMI audio helpers

[Maxime Ripard]

Hi,

On Wed, May 27, 2026 at 04:53:29PM +0800, wangdich9700@xxxxxxx wrote:
> From: wangdicheng <wangdicheng@xxxxxxxxxx>
> 
> The DRM HDMI audio helper framework notifies the audio codec about
> physical connection changes via drm_connector_hdmi_audio_plugged_notify(),
> but has no mechanism to notify when the CRTC state changes while the
> connector remains physically connected.
> 
> This is a real problem on platforms with DP/HDMI audio. When a CRTC is
> disabled while the sink remains connected (e.g. user switches to
> "internal display only" mode but still wants audio from the external
> monitor), the audio path silently breaks because:
> 
> 1. The video stream is disabled, so there are no blanking intervals
>    for audio Secondary Data Packets (SDP) to be transported.
> 
> 2. The audio codec still believes the jack is present because
>    plugged_notify() was not called (the connector is still physically
>    connected).
> 
> 3. Userspace (PulseAudio/PipeWire) continues routing audio to the
>    external display, but no sound is actually output.
> 
> Without a framework-level notification, vendors who need to support
> "audio output to external display while CRTC is inactive" are forced
> to scatter condition checks across CRTC disable, encoder disable,
> suspend, and resume paths. This pattern is fragile: any change in
> the display pipeline can break the audio path, and the same condition
> ("connector connected but CRTC inactive, and audio is in use") must
> be duplicated in multiple locations.
> 
> The root cause is architectural: the audio codec has no visibility
> into CRTC state changes, so there is no clean way to implement
> policies like:
> 
> - Mute audio output when CRTC is disabled (instead of silent breakage)
> - Keep the video stream alive for audio transport
> - Switch to DP Audio Only mode (hardware-supported on some platforms,
>   e.g. Intel TRANS_DP_AUDIO_ONLY, but never used in i915 driver)
> 
> The HDA HDMI silent stream / KAE mechanism partially addresses this on
> Intel platforms, but it operates only on the audio codec side and does
> not coordinate with the DRM side. It also cannot work on platforms
> without HDA codec support (e.g. ASoC-based designs).
> 
> Add an optional callback crtc_state_change() to
> drm_connector_hdmi_audio_funcs, and a corresponding notification
> function drm_connector_hdmi_audio_crtc_notify(). DRM drivers should
> call this when the CRTC state changes on a connector with audio
> capability, allowing audio codec implementations to react to display
> pipeline state changes rather than only physical connection changes.
> 
> This provides a framework-level mechanism to implement "audio without
> active display" policies cleanly, instead of scattering condition
> checks across the display pipeline.
> 
> Signed-off-by: wangdicheng <wangdicheng@xxxxxxxxxx>

I'm not saying this is right or wrong, but I'd like to see what it looks
like from a driver point of view before merging anything in the
framework.

Maxime

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