HDMI Audio on Optimus system

Question

I have an Asus G46vw (specs below) running Ubuntu 14.04 build 05/05/14 and this laptop has Intel Card and a discrete 660M. I am very excited to have HDMI working with Optimus. But I have one last thing that is driving me nuts. Audio over HDMI.

I have tried googled the crap out of this issue and I am pretty good at figuring things out for myself through forum reading but I have had no luck so far. Pulseaudio does not list my HDMI output. Maybe I need to update Pulse Audio? Below is more info.

List of PLAYBACK Hardware Devices

# aplay -l
card 0: PCH [HDA Intel PCH], device 0: VT1802 Analog [VT1802 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 1: VT1802 Digital [VT1802 Digital]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 2: VT1802 Alt Analog [VT1802 Alt Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0


# cat /proc/asound/cards 
 0 [PCH            ]: HDA-Intel - HDA Intel PCH
                      HDA Intel PCH at 0xf7a10000 irq 46

Answer 1

I managed to get HDMI audio output working on my laptop with "NVIDIA Corporation GF116M [GeForce GT 555M/635M]" GPU, using the nvidia driver and nvidia-prime. The process is rather convoluted and you have to perform it after every reboot. I've written a script that automates the process as much as possible. Its comments explain what it does. (Edit: If you don't like running the script, you can also follow the procedure described here: https://askubuntu.com/a/660910/73753)

#!/bin/bash

# Check if we are executing as root
if [ $UID != 0 ]; then
    echo "This script must be run as root."; exit
fi

# The nvidia driver cannot be loaded while we are configuring the GPU.
# Check whether the nvidia kernel is loaded:
if grep nvidia /proc/modules; then
    # It is. Check if we have HDMI audio
    if lspci | grep 01:00.1; then
        # Yes, so we are already done.
        echo "The following list should contain HDMI audio devices"
        aplay -l
        alsa reload
        echo "--> You are done!"; exit
    else
        # No, disable output through nvidia:
        prime-select intel
        echo "Please reboot. Afterwards rerun this script."; exit
    fi
fi

# Make sure that the GPU is powered
if ! lspci -H1 | grep 01:00.0; then
    if ! grep OFF /proc/acpi/bbswitch; then
        echo "ERROR: GPU is listed in lspci -H1, but bbswitch thinks it is off"; exit 1
    fi
    # Turn on the discrete GPU (to get it listed in `lspci -H1`)
    echo ON > /proc/acpi/bbswitch
    if ! grep ON /proc/acpi/bbswitch; then
        echo "ERROR: Failed to turn on the GPU"; exit 1
    fi
fi

# Check if the GPU's audio chip is powered
if ! lspci -H1 | grep 01:00.1; then
    echo "Suspend the pc and resume it again. This will turn on the audio chip on the discrete GPU. Afterwards rerun this script."; exit
fi

# The output of 'lscpi -H1' should now contain 2 lines similar to:
# 01:00.0 VGA compatible controller: NVIDIA Corporation GF116M [GeForce GT 555M/635M] (rev a1)
# 01:00.1 Audio device: NVIDIA Corporation GF116 High Definition Audio Controller (rev a1)

# Now we need to rescan for the GPU such that the audio chip is found as well
if lspci | grep 01:00.0; then
    # Now we 'unmount' the GPU
    # the nvidia driver is not loaded, otherwise this step would eventualy cause your computer to freeze/hang
    echo 1 > /sys/bus/pci/devices/0000\:01\:00.0/remove
    # Wait a bit
    sleep 1
    # Check if this succeeded
    if ! lspci | grep 01:00.0; then
        echo "ERROR: Failed to remove the GPU (or so it seems, you can try again)"; exit 1
    fi
fi

if ! lspci | grep 01:00.0; then
    # Rescan
    echo 1 > /sys/bus/pci/rescan
    if ! lspci | grep 01:00.1; then
        echo "ERROR: Rescan did not find the audio chip"; exit 1
    fi

    # The output of 'lspci' should now contain 2 lines similar to:
    # 01:00.0 VGA compatible controller: NVIDIA Corporation GF116M [GeForce GT 555M/635M] (rev a1)
    # 01:00.1 Audio device: NVIDIA Corporation GF116 High Definition Audio Controller (rev a1)

    # Now we are ready to restart X11 using the nvidia driver
    prime-select nvidia
    echo "Please log out and in again. Afterwards rerun this script."; exit
fi

echo "ERROR: Something went wrong"; exit 1

Answer 2

OK, so the following works for nvidia-384 proprietary driver, installed with nvidia-prime on Ubuntu Gnome 16.04.3. Theoratically it should work for all Nvidia optimus chipsets.

$ sudo prime-select intel
$ sudo reboot
// After the reboot and login
$ sudo lspci -H1 | grep -i nvidia

This would show you only the VGA controller, not the audio chip. To enable the audio chip, execute the following commands.

$ sudo su
# setpci -s 01:00.0 0x488.l=0x2000000:0x2000000
# echo 1 > /sys/bus/pci/devices/0000\:01\:00.0/remove
// where 0000:01:00.0 is your VGA device in sysfs PCI heirarchy.
# echo "1" > /sys/bus/pci/rescan
# lspci -H1 | grep -i nvidia

This time it would show you the audio chip as well. e.g. for me, the last command shows:

01:00.0 VGA compatible controller: NVIDIA Corporation GK107GLM [Quadro K1100M] (rev a1) 01:00.1 Audio device: NVIDIA Corporation GK107 HDMI Audio Controller (rev a1)

Now you need to get the environment setup and load Nvidia drivers. For that purpose, exit root shell, set nvidia as prime device and restart the display manager i.e.

# exit
$ sudo prime-select nvidia
$ sudo service gdm restart

After login, the driver registers the audio controller with Alsa and hence you can select HDMI audio in sound settings now. Hope this helps someone.