[alsa-devel] ??????: [PATCH] vgaswitchroo: set audio client id according to bound gpu client id

[Lukas Wunner]

On Mon, Jul 09, 2018 at 05:04:22PM +0200, Takashi Iwai wrote:
> On Mon, 09 Jul 2018 15:58:51 +0200, Alex Deucher wrote:
> > On Mon, Jul 9, 2018 at 6:16 AM, Qu, Jim <Jim.Qu at amd.com> wrote:
> > > > You're saying above that the HDA controller isn't runtime resumed on
> > > > hotplug of a display.  Is that necessary to retrieve ELD or something?
> > > > I'm not sure if there's code in the HDA driver to acquire a runtime PM
> > > > ref on HPD, but maybe it's necessary.  Or maybe the code is there but
> > > > somehow no HPD interrupt is received by the HDA driver?
> > >
> > > So far, I do not find any code about audio response HPD in kernel.
> > > the HPD interrupt will sent to user mode via uevent, not sure whether
> > > audio user mode driver can receive the event or not.
> > 
> > On the gfx side at least, we can get a hotplug event via ACPI
> > (depending on the OEM design) if displays are attached/detached while
> > the dGPU is powered down.  I suppose the gfx driver could call into
> > the audio driver during one of those events.  On the gfx side at least
> > we just generate the gfx hotplug event and let userspace deal with it.
> 
> IMO, a more proper way would be to have the direct communication
> between the graphics driver and the audio driver like i915 driver
> does.  Then the audio driver can get plug/unplug event at more
> accurate timing without races.

Since v4.17, every time the GPU is powered up, the HDA controller is
runtime resumed to PCI_D0.  (See the call to pci_wakeup_bus() in
vga_switcheroo_runtime_resume() added by dcac86b7d0.)

If the HDA controller can't detect presence of an HDMI display even
if it's in PCI_D0, then I suppose that needs to be adressed in the HDA
driver.  Thus so far I don't see the need to call from amdgpu into the
HDA driver.

Thanks,

Lukas