[Bug 101900] No HDMI HBR audio on Polaris (no TrueHD, no Atmos, no Neo:X, no HD Master audio)

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Wed Aug 9 19:29:14 UTC 2017


https://bugs.freedesktop.org/show_bug.cgi?id=101900

--- Comment #6 from Alex Deucher <alexdeucher at gmail.com> ---
Here's the relevant ALSA code:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/sound/pci/hda/hda_eld.c
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/sound/pci/hda/patch_hdmi.c
The display driver parses the audio capabilities of the monitor and then passes
that information to the audio driver via a shared structure called the ELD. 
AMD hardware doeswn't use an ELD directly since display audio support on AMD
hardware pre-dated ELD.  Instead, the display driver writes fills in the audio
descriptors from the monitor into registers that are shared between the audio
hardware and the display hardware.  The audio driver then parses these
registers and generated and ELD which is used by the audio driver to determine
what audio modes are supported by the display.  See snd_hdmi_get_eld_ati(). 
See patch_atihdmi() for how the streams are set up on the audio side.

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