[Nouveau] [PATCH] PCI: Expose hidden NVIDIA HDA controllers

[Ilia Mirkin]

On Thu, Jun 13, 2019 at 9:15 AM Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>
> On Thu, Jun 13, 2019 at 2:35 AM Daniel Drake <drake at endlessm.com> wrote:
> >
> > From: Lukas Wunner <lukas at wunner.de>
> >
> > The integrated HDA controller on Nvidia GPUs can be hidden with a bit in
> > the GPU's config space. Information about this scheme was provided by
> > NVIDIA on their forums.
> >
> > Many laptops now ship with this device hidden, meaning that Linux users
> > of affected platforms (where the HDMI connector comes off the NVIDIA GPU)
> > cannot use HDMI audio functionality.
> >
> > Avoid this issue by exposing the HDMI audio device on device enumeration
> > and resume.
> >
> > The GPU and HDA controller are two functions of the same PCI device
> > (VGA class device on function 0 and audio device on function 1).
> > The multifunction flag in the GPU's Header Type register is cleared when
> > the HDA controller is hidden and set if it's exposed, so reread the flag
> > after exposing the HDA.
> >
> > According to Ilia Mirkin, the HDA controller is only present from MCP89
> > onward, so do not touch config space on older GPUs.
>
> Actually GF100 also has it, and has a lower PCI ID than MCP89. But I
> don't think it really matters - I can't imagine anyone played HDA
> hiding tricks on that power-hungry monster. I'd appreciate it if you
> could reword this sentence to imply that it's on PCI IDs >= MCP89's
> rather than GPUs newer than MCP89. GT215 was released before MCP89,
> I'm fairly sure, but its PCI ID comes later, for example. [Wikipedia
> says November 17, 2009 for GT215 vs some point in 2010 for MCP89.]
> Maybe like
>
> "..., the HDA controller is only present on GPUs with PCI IDs values
> from MCP89's and onward, so ..."
>
> >
> > This quirk is limited to NVIDIA PCI devices with the VGA Controller
> > device class. This is expected to correspond to product configurations
> > where the NVIDIA GPU has connectors attached. Other products where the
> > device class is 3D Controller are expected to correspond to configurations
> > where the NVIDIA GPU is dedicated (dGPU) and has no connectors.
> >
> > It's sensible to avoid exposing the HDA controller on dGPU setups,
> > especially because we've seen cases where the PCI BARs are not set
> > up correctly by the platform in this case, causing Linux to log
> > errors if the device is visible. This assumption of device class
> > accurately corresponding to product configuration is true for 6 of 6
> > laptops recently checked at the Endless lab, and there are also signs of
> > agreement checking the data from 74 previously tested products, however
> > Ilia Mirkin comments that he's seen cases where it is not true. Anyway, it
> > looks like this quirk should fix audio support for the majority of
> > affected users.
>
> Yeah, this is fine. We used to have code which prevented enabling the
> display portion when 3d class != VGA. We had to change it :) So I'm
> definitely not making things up... However whether any of those people
> *also* had HDA hiding issues -- unknown. And it wouldn't make things
> any worse for them.

FTR, this is where it was enabled:

commit fc1620883af8cbc10bfb1a4ef2eb4e8113243012
Author: Ben Skeggs <bskeggs at redhat.com>
Date:   Tue Sep 10 13:20:34 2013 +1000

    drm/nouveau/kms: enable for non-vga pci classes

    Signed-off-by: Ben Skeggs <bskeggs at redhat.com>

Unfortunately no bug id included.