The ELD Port_ID field (bytes 8..15 of the baseline block) is typically zero on Linux today: drm_edid_to_eld() leaves it empty and no in-tree driver fills it in. amdgpu, radeon and nouveau pass the raw connector->eld to the audio component. On the amdgpu DC Azalia register path the value is a hardcoded constant, the same for every port. Only closed display drivers fill the value.
Pipewire added support for "Port_ID" in merge request: https://gitlab.freedesktop.org/pipewire/pipewire/-/merge_requests/3025 As a result, when two identical monitors are connected their ELDs are byte-identical, and userspace (e.g. PipeWire/WirePlumber) cannot passively tell which HDMI/DP PCM belongs to which DRM connector. This series adds a DRM helper that fills Port_ID with a common layout, and uses it in i915: bits 63:48 - PCI domain of the DRM device bits 47:32 - PCI bus/device/function of the DRM device bits 31:0 - DRM connector object ID The upper half follows the layout documented for the AMD Azalia sink info registers (dce_audio.c: "PORT_ID1 = 16bit BDF"). The aim is for this to become a convention other drivers can opt into. For drivers that copy connector->eld to the audio component (amdgpu DM, radeon, nouveau), adopting it would be a one-line change. Comments from the AMD and nouveau folks on whether the layout works for them are very welcome. An alternative would be to fill Port_ID directly in drm_edid_to_eld(), so every driver gets it without changes. I went with an opt-in helper to avoid changing the ELD contents seen by all drivers and existing userspace at once. The value is exposed to userspace via the ALSA ELD control and /proc/asound/cardX/eld#Y. Kai Vehmanen (2): drm/eld: Add drm_eld_set_port_id() helper drm/i915/audio: Populate ELD Port_ID drivers/gpu/drm/drm_eld.c | 42 ++++++++++++++++++++++ drivers/gpu/drm/i915/display/intel_audio.c | 2 ++ include/drm/drm_eld.h | 3 ++ 3 files changed, 47 insertions(+) -- 2.43.0
