Possible to modify Intel HDMI Audio registry settings to get HDMI audio working?

[richb93]

Given that HDMI audio works in Linux, I assume Linux is doing something when probing the HD audio side of things.

I've been poking around in the Intel HDMI audio driver, and notice that it puts various settings into the registry to configure the HDMI audio device, including the Pin config, as well as initialisation verbs.

I am not too well clued up with this kind of thing, but I do have memories of playing around with Pin configs to get optimal audio from the HD audio device on my hackintosh back in the day.

Could it be that the Intel HDMI audio needs to be modified in a suitable manner to initialise properly?

For what it's worth, I was playing around with the various registry keys (adding keys in as found in the IntcHdmi.sys file) and the display driver then crashed before the system rebooted, so I was definitely able to influence a change, albeit not successful.

Apologies that I can't offer any actual answer here, but hopefully someone with a bit more understanding with regards to how the HD audio standard works can figure out what needs changing to get this working.

Thanks!

[DistroHopper39B]

My theory as to why HDMI audio doesn't work is that it fails when the GPU driver isn't running. It's probably possible to get HDMI audio working if there is some way to stop that check from happening, but I wouldn't know where to start with that - static analysis in Ghidra or alike would probably be required.

[richb93]

That's understandable. I know in the past I've seen a lot of things get set by some low level hardware poking, so to that end, I guess something could be added to the boot loader to 'set up' the device to work as expected? To that end, I wonder if any poking can be done to the onboard audio to fix the output levels. Again, apologies for theorising stuff without any actual solutions to back it up!

Thank you so much for your amazing work on this - this thing makes an awesome little retro games box thanks to that surprisingly powerful GeForce they included.

[richb93]

I've dumped a number of bits and bobs from the system whilst running under Linux which may help. From what I can tell, HDMI audio is covered by the Silicon Image SiI1390 Sil1930 HDMI chip which has also been used on ATI and NVIDIA cards from around 2006. My understanding is that this chip can take in a digital video signal and also an audio stream in I2S, SPDIF or HDA format and mux them together. So with this information I'm hoping that there is no relation to initialising an Intel iGPU, and it's just the case of getting the HDA stuff in the chipset to initialise and play ball.

I wish I could provide some more input, but I hope this helps someone out who may be interested in taking this on.

dumps.tar.gz

EDIT: The thick plottens... So the chip is identified as a Sil1390 in Linux (because the PID of the device is 1390 for some reason), and in some historical documentation on how to run XBMC on the ATV it appears you had to select ATI HDMI for audio. But the Sil1390 is specifically for Intel GPUs, using SVDO to get the video stream instead of TDMS. The Sil1930 was used on ATI and NVIDIA graphics cards to get TDMS video and mux it with audio - on NVIDIA cards, this was done by means of requiring an SPDIF input on the graphics card (i.e. not handled at a driver level). On ATI cards, they actually provided an HD audio driver which send HDA compliant audio to the Sil1930.

I've tried the ATI driver to no success on my machine. The next steps I was tempted to try was to see what verbs Linux sends to the chip to set up audio - but to do HDA audio debug you need a kernel that is compiled with HDA debug support (at least as far as I can tell).

Basically, it's a very weird setup. I wonder if you could initialise it during the boot loader process by poking it?

[Piggyhero2006]

I don't know if this contributes to anything, but I was able to get the Nvidia HD audio driver to install that came with the newer Nvidia display driver. It gives error code 10 that the device cannot start. When I tried with other random realtek drivers it always gave a BSOD but somehow the nvidia one installed. I know nothing of how these audio drivers work so I'm just trying random different things.

[DistroHopper39B]

I don't know if this contributes to anything, but I was able to get the Nvidia HD audio driver to install that came with the newer Nvidia display driver. It gives error code 10 that the device cannot start. When I tried with other random realtek drivers it always gave a BSOD but somehow the nvidia one installed. I know nothing of how these audio drivers work so I'm just trying random different things.

The HDMI audio is run through the Intel chipset, not the NVIDIA card. For some reason.

[Piggyhero2006]

I was able to get a newer version of a realtek driver installed but it didn't change anything. I noticed that there is an unknown device for audio in the device manager. Is that used for anything or should it be left untouched?

[DistroHopper39B]

That's the Intel HDMI audio port. You can extract and install the driver from the Intel GMA 950 driver but it doesn't work (no audio devices show up)

[mantheman]

Was and is not always straightforward with HDMI Audio under Linux either:
HDMI Audio was borked under Linux for a long time. For many years only the V10x.x something driver worked. It wasn't until Nvidia fixed it later on it worked. If I remember correctly it was at the request of Davilla, who wrote the CrystalHD driver/ATV-bootloader.
Something has changed during the latest kernels as it no longer works under kernel 5.0+. (There are patches for the Nvidia 304.137 driver to build at least up to 6.12)

[DistroHopper39B]

Does HDMI audio really go through the NVIDIA card? Windows Device Manager seems to imply it goes through the Intel chipset, but that could be a device that has no actual output. OSMC (latest version) doesn't seem to support HDMI audio when I tested (could have tested wrong tho) and I think it's pretty likely that upstream Linux doesn't support RCA audio correctly but I haven't tested it (the patches that exist for Linux 2.6.whatever probably aren't too difficult to adapt to modern kernels).

[mantheman]

Does HDMI audio really go through the NVIDIA card? Windows Device Manager seems to imply it goes through the Intel chipset, but that could be a device that has no actual output. OSMC (latest version) doesn't seem to support HDMI audio when I tested (could have tested wrong tho) and I think it's pretty likely that upstream Linux doesn't support RCA audio correctly but I haven't tested it (the patches that exist for Linux 2.6.whatever probably aren't too difficult to adapt to modern kernels).

Yeah I think audio is passthrough the HDMI port, but actually comes from the Intel chip. In Linux it all comes from the same device. Analog is hw0,0 , toslink hw0,1, HDMI hw0,3.

RCA/Analog and optical works fine in Linux.