[Nouveau] [Bug 75985] [NVC1] HDMI audio device only visible after rescan

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=75985

--- Comment #70 from Aaron Plattner <aplattner at nvidia.com> ---
How the audio and video drivers interact is described a bit in [1]: The audio
function and the graphics function work hand-in-hand to provide audio support.
At modeset time, the graphics driver extracts information from the display's
EDID and the mode timings and sticks it into registers in the graphics
function. These get processed by the hardware and spit out the other side via
the "EDID-Like Data" fields in the audio function, described in [2].

I'm not completely sure how this works on Windows, but my understanding is that
the display driver enables or disables the audio function at modeset time, and
Windows handles that as a PCI hot-plug or -unplug, loading or unloading the
audio driver as necessary. On Linux, I think the nouveau and nvidia-modeset
drivers would need to call into some hypothetical new audio power module to
coordinate that, so the kernel can know when to rescan or remove the audio
device.

[1]
https://download.nvidia.com/XFree86/gpu-hdmi-audio-document/#_driver_architecture
[2]
https://www.intel.com/content/www/us/en/standards/high-definition-audio-specification.html

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