Hi

I have a Dell XPS 15 laptop with Optimus.
It has the following NVIDIA card:
01:00.0 VGA compatible controller: NVIDIA Corporation GF108M [GeForce GT 540M]
(rev a1)

The HDMI output is working fine since some time now.
Only there is still an issue with the HDMI audio.

On Windows, and with `lspci -H1` it shows the following devices:
01:00.0 VGA compatible controller: NVIDIA Corporation GF108M [GeForce GT 540M]
(rev a1)
01:00.1 Audio device: NVIDIA Corporation GF108 High Definition Audio Controller
(rev a1)

But by default, the audio device isn't visible after a clean boot. So the HDMI
audio ain't working.

Now I've found some workaround to get it working.

- Start the system, and stop the display manager (lightdm/gdm)
- Load the nouveau module
- Remove the Nvidia card from the PCI bus (echo 1 >
/sys/bus/pci/devices/0000\:01\:00.0/remove)
- Rescan the PCI bus (echo "1" > /sys/bus/pci/rescan)

And there it is, the Audio device is visible now:
01:00.0 VGA compatible controller: NVIDIA Corporation GF108M [GeForce GT 540M]
(rev a1)
01:00.1 Audio device: NVIDIA Corporation GF108 High Definition Audio Controller
(rev a1)

Also dmesg shows the following:
[  152.360864] input: HDA NVidia HDMI/DP,pcm=9 as
/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1/input18
[  152.361210] input: HDA NVidia HDMI/DP,pcm=8 as
/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1/input17
[  152.361415] input: HDA NVidia HDMI/DP,pcm=7 as
/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1/input16
[  152.361592] input: HDA NVidia HDMI/DP,pcm=3 as
/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1/input15

So the device is loaded correctly.
Now if we start lightdm/gdm/whatever again, and login (which also starts
PulseAudio), the HDMI audio works correctly like it should :)

Some note:
If we do the rescan without nouveau module loaded, the workaround does not
work. So we need to have nouveau loaded to make the Audio device visible.

On first boot I get the following error:
[  121.872253] nouveau 0000:01:00.0: enabling device (0006 -> 0007)
[  121.872554] [drm] hdmi device  not found 1 0 1

This might be related?
After the rescan, it shows the following:
[  151.557038] [drm] Initialized nouveau 1.1.1 20120801 for 0000:01:00.0 on
minor 1
[  151.557186] snd_hda_intel 0000:01:00.1: enabling device (0000 -> 0002)
[  151.557253] hda_intel: Disabling MSI
[  151.557274] hda-intel 0000:01:00.1: Handle VGA-switcheroo audio client
[  151.557349] hda-intel 0000:01:00.1: Disabling 64bit DMA
[  151.560778] hda-intel 0000:01:00.1: Enable delay in RIRB handling
[  152.360864] input: HDA NVidia HDMI/DP,pcm=9 as
/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1/input18
[  152.361210] input: HDA NVidia HDMI/DP,pcm=8 as
/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1/input17
[  152.361415] input: HDA NVidia HDMI/DP,pcm=7 as
/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1/input16
[  152.361592] input: HDA NVidia HDMI/DP,pcm=3 as
/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1/input15
[  156.801404] hda-intel 0000:01:00.1: Disabling via VGA-switcheroo

Hopefully this can help getting the issue fixed completely :)

Thanks!
Jean-Louis