No audio with successful iGPU HDMI passthrough any ideas?

[privatesam]

I've successfully passed through iGPU to an Ubuntu VM I've built using the instructions on Proxmox 8. The motherboard I'm using is E3C246D4U2-2T with a Intel Core i5-8500 CPU but I'm not getting any audio.
Here is the VM conf:

Everything is working except audio. Audio issues are discussed here: #1 and @LongQT-sea suggested the following:

You also need to passthrough the PCH audio controller to the VM.
On my PC, the PCH audio controller looks like this:
00:1f.3 Audio device [0403]: Intel Corporation 200 Series PCH HD Audio [8086:a2f0]

However on my Proxmox host I don't have any PCH audio controllers listed:

root@husk:~# lspci
00:00.0 Host bridge: Intel Corporation 8th Gen Core Processor Host Bridge/DRAM Registers (rev 07)
00:01.0 PCI bridge: Intel Corporation 6th-10th Gen Core Processor PCIe Controller (x16) (rev 07)
00:02.0 Display controller: Intel Corporation CoffeeLake-S GT2 [UHD Graphics 630]
00:08.0 System peripheral: Intel Corporation Xeon E3-1200 v5/v6 / E3-1500 v5 / 6th/7th/8th Gen Core Processor Gaussian Mixture Model
00:12.0 Signal processing controller: Intel Corporation Cannon Lake PCH Thermal Controller (rev 10)
00:14.0 USB controller: Intel Corporation Cannon Lake PCH USB 3.1 xHCI Host Controller (rev 10)
00:14.2 RAM memory: Intel Corporation Cannon Lake PCH Shared SRAM (rev 10)
00:15.0 Serial bus controller: Intel Corporation Cannon Lake PCH Serial IO I2C Controller #0 (rev 10)
00:15.1 Serial bus controller: Intel Corporation Cannon Lake PCH Serial IO I2C Controller #1 (rev 10)
00:16.0 Communication controller: Intel Corporation Cannon Lake PCH HECI Controller (rev 10)
00:16.1 Communication controller: Intel Corporation Device a361 (rev 10)
00:16.4 Communication controller: Intel Corporation Cannon Lake PCH HECI Controller #2 (rev 10)
00:17.0 SATA controller: Intel Corporation Cannon Lake PCH SATA AHCI Controller (rev 10)
00:1b.0 PCI bridge: Intel Corporation Cannon Lake PCH PCI Express Root Port #17 (rev f0)
00:1b.4 PCI bridge: Intel Corporation Cannon Lake PCH PCI Express Root Port #21 (rev f0)
00:1c.0 PCI bridge: Intel Corporation Cannon Lake PCH PCI Express Root Port #1 (rev f0)
00:1d.0 PCI bridge: Intel Corporation Cannon Lake PCH PCI Express Root Port #9 (rev f0)
00:1e.0 Communication controller: Intel Corporation Cannon Lake PCH Serial IO UART Host Controller (rev 10)
00:1f.0 ISA bridge: Intel Corporation Cannon Point-LP LPC Controller (rev 10)
00:1f.4 SMBus: Intel Corporation Cannon Lake PCH SMBus Controller (rev 10)
00:1f.5 Serial bus controller: Intel Corporation Cannon Lake PCH SPI Controller (rev 10)
01:00.0 VGA compatible controller: NVIDIA Corporation GA104 [GeForce RTX 3070] (rev a1)
01:00.1 Audio device: NVIDIA Corporation GA104 High Definition Audio Controller (rev a1)
03:00.0 Ethernet controller: Intel Corporation Ethernet Controller X550 (rev 01)
03:00.1 Ethernet controller: Intel Corporation Ethernet Controller X550 (rev 01)
04:00.0 PCI bridge: ASPEED Technology, Inc. AST1150 PCI-to-PCI Bridge (rev 04)
05:00.0 VGA compatible controller: ASPEED Technology, Inc. ASPEED Graphics Family (rev 41)
06:00.0 Non-Volatile memory controller: Micron/Crucial Technology P310 NVMe PCIe SSD (DRAM-less) (rev 01)

(obviously except for the Nvidia one but thats passed through to a different VM as part of a RTX3070)

Would anyone know if I'm just missing the architecture on this board (Intel C246) to do this? @logan893 would you know anything about this as you're using the same chipset?

Thanks for any help.

[LongQT-sea]

According to the C246 chipset page on Intel.com, your chipset does include an audio controller. I suggest checking the Audio Controller option in your BIOS/UEFI settings.

[LongQT-sea]

Oops, looks like your BIOS has the audio controller hidden.
https://download.asrock.com/Manual/E3C246D4U2-2T.pdf

In this case you need to somehow change the hidden option using grub-mod-setup_var or the EFI shell (or go advanced with RU.efi from https://ruexe.blogspot.com/).
Be careful when using RU.efi, because if you mess something up, you’ll need to clear CMOS to recover.

[privatesam]

I had a good look through the BIOS, even the hidden menu settings but as you suggest it appears to have been disabled on this board. I'm trying to see if a later BIOS maybe has a setting for it but I don't think so. I suspect editing things using RU.efi etc is beyond me. Maybe someone will find this thread at some point and be able to suggest something. Thanks for your help though.
I tested a USB sound card passed through to the VM and it worked. But would make life easier if it went via HDMI - I wonder if theres a device that can inject sound from a sound card into the HDMI or something.

[logan893]

@privatesam I can get audio out via HDMI if I also passthrough the audio device (00:1f.3).

However, the audio device shares the same IOMMU group with adjacent devices (00:1f.*) and they all switch to the vfio-pci driver.

This may or may not be desirable for you. In my case, it's grouped with one of my on-board NICs, so I have a choice to make.

I have not yet tried the "pcie_acs_override=downstream" kernel command line option, to see if this changes anything.

More info about IOMMU:
https://pve.proxmox.com/wiki/PCI_Passthrough
https://vfio.blogspot.com/2014/08/iommu-groups-inside-and-out.html

# lspci -s 00:1f.3 -vvv
00:1f.3 Audio device: Intel Corporation Cannon Lake PCH cAVS (rev 10)
        DeviceName: Onboard - Sound
        Subsystem: ASRock Incorporation Device 5892
        Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 32, Cache Line Size: 64 bytes
        Interrupt: pin A routed to IRQ 170
        IOMMU group: 14
        Region 0: Memory at a2330000 (64-bit, non-prefetchable) [size=16K]
        Region 4: Memory at a2000000 (64-bit, non-prefetchable) [size=1M]
        Capabilities: [50] Power Management version 3
                Flags: PMEClk- DSI- D1- D2- AuxCurrent=55mA PME(D0-,D1-,D2-,D3hot+,D3cold+)
                Status: D0 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME-
        Capabilities: [80] Vendor Specific Information: Len=14 <?>
        Capabilities: [60] MSI: Enable+ Count=1/1 Maskable- 64bit+
                Address: 00000000fee00318  Data: 0000
        Kernel driver in use: snd_hda_intel
        Kernel modules: snd_hda_intel, snd_soc_avs, snd_sof_pci_intel_cnl

Add device, no special flags needed in my case.

# qm shutdown 100
# qm set 100 -hostpci1 0000:00:1f.3
# qm start 100

Result: all devices sharing the same IOMMU group need to swap driver. If I use this on-board NIC to access the system, I may be locked out (both console gone, and no network access) when I start this VM.

# lspci -s 00:1f -vv
00:1f.0 ISA bridge: Intel Corporation C246 Chipset LPC/eSPI Controller (rev 10)
        DeviceName: Onboard - Other
        Subsystem: ASRock Incorporation Device a309
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
        Status: Cap- 66MHz- UDF- FastB2B- ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 0
        IOMMU group: 14
        Kernel driver in use: vfio-pci

00:1f.3 Audio device: Intel Corporation Cannon Lake PCH cAVS (rev 10)
        DeviceName: Onboard - Sound
        Subsystem: ASRock Incorporation Device 5892
        Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 32, Cache Line Size: 64 bytes
        Interrupt: pin A routed to IRQ 170
        IOMMU group: 14
        Region 0: Memory at a2330000 (64-bit, non-prefetchable) [size=16K]
        Region 4: Memory at a2000000 (64-bit, non-prefetchable) [size=1M]
        Capabilities: [50] Power Management version 3
                Flags: PMEClk- DSI- D1- D2- AuxCurrent=55mA PME(D0-,D1-,D2-,D3hot+,D3cold+)
                Status: D0 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME-
        Capabilities: [80] Vendor Specific Information: Len=14 <?>
        Capabilities: [60] MSI: Enable+ Count=1/1 Maskable- 64bit+
                Address: 00000000fee00318  Data: 0000
        Kernel driver in use: vfio-pci
        Kernel modules: snd_hda_intel, snd_soc_avs, snd_sof_pci_intel_cnl

00:1f.4 SMBus: Intel Corporation Cannon Lake PCH SMBus Controller (rev 10)
        DeviceName: Onboard - Other
        Subsystem: ASRock Incorporation Device a323
        Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
        Status: Cap- 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Interrupt: pin A routed to IRQ 16
        IOMMU group: 14
        Region 0: Memory at a2338000 (64-bit, non-prefetchable) [size=256]
        Region 4: I/O ports at efa0 [size=32]
        Kernel driver in use: vfio-pci
        Kernel modules: i2c_i801

00:1f.5 Serial bus controller: Intel Corporation Cannon Lake PCH SPI Controller (rev 10)
        DeviceName: Onboard - Other
        Subsystem: ASRock Incorporation Device a324
        Control: I/O- Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
        Status: Cap- 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        IOMMU group: 14
        Region 0: Memory at fe010000 (32-bit, non-prefetchable) [size=4K]
        Kernel driver in use: vfio-pci
        Kernel modules: spi_intel_pci

00:1f.6 Ethernet controller: Intel Corporation Ethernet Connection (7) I219-LM (rev 10)
        DeviceName: Onboard - Ethernet
        Subsystem: ASRock Incorporation Device 15bb
        Control: I/O- Mem- BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Interrupt: pin A routed to IRQ 16
        IOMMU group: 14
        Region 0: Memory at a2300000 (32-bit, non-prefetchable) [disabled] [size=128K]
        Capabilities: [c8] Power Management version 3
                Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA PME(D0+,D1-,D2-,D3hot+,D3cold+)
                Status: D3 NoSoftRst+ PME-Enable+ DSel=0 DScale=1 PME-
        Capabilities: [d0] MSI: Enable- Count=1/1 Maskable- 64bit+
                Address: 0000000000000000  Data: 0000
        Kernel driver in use: vfio-pci
        Kernel modules: e1000e

[LongQT-sea]

If you want to use that NIC, you need to passthrough it to the same VM as the audio controller. Then, in the VM’s Hardware tab, add another virtual NIC. Inside the VM:

• For Linux: create a bridge and add both NICs (the passthrough and the virtual one) to it.
• For Windows: Run ncpa.cpl then hold Ctrl, select both the passthrough NIC and the virtual NIC, right-click, and choose Bridge Connections.
• For macOS: open Settings >> Network >> Manage Virtual Interfaces >> add New bridge >> select both the virtual NIC and the passthrough NIC then Create.

No Layer 3 (IP address) configuration is needed. This effectively turns your real NIC into a switch.

[logan893]

I just tried adding "pcie_acs_override=downstream" to the kernel command line, but unfortunately it does not split this group into separate IOMMUs.

I am personally not going to bridge a network device via a VM this way, but it might be an option for some.

[codyrocco]

Here, with a NUC 9 Extreme...
Video passtrough worked perfectly, as long as I don't try to use "select all functions" or "primary gpu" options - this will trigger error 43, requiring removing and adding again the video card.
Audio, not so. This one has a cAVS, in the same IOMMU group with SMBus controller, SPI controller and one of ethernets (219LM). ACS override doesn't have effect here (although I obtained excellent results for CPU PCIE x16 splitting!). Shortly after entering the Windows GUI, the screen will flicker a bit, then no more signal for HDMI. Somehow I obtained a DP signal, over Thundebolt, but unusable. Using a remote desktop solution (Dameware), I was able to see both devices installed correctly, only no video signal.
I should specify that I tried with both 9 and 9.1 versions of ROM.