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

[Lukas Wunner <lukas-JFq808J9C/izQB+pC5nmwQ@public.gmane.org>]

On Mon, Jul 09, 2018 at 05:52:49PM +0200, Takashi Iwai wrote:
> On Mon, 09 Jul 2018 17:47:34 +0200, Lukas Wunner wrote:
> > 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.
> 
> It's not about the PCI power state, but the problem is that the
> detection of the HDMI and its ELD read is somewhat asynchronous.
> Basically it's handled via the hardware unsolicited event emitted over
> HD-audio bus, which was originally generated by GPU at dealing with
> the hotplug/unplug.  So, this part is racy and not 100% reliable --
> although usually it shouldn't be a big problem.
> 
> That said, it's not the exact "need" but it would make things more
> reliable and accurate (even consumes less power as we don't need to
> power up/down just for the HDMI detection).

Okay.  If amdgpu triggers the event on the HDA bus, it should call
pm_runtime_get_sync() on the HDA device beforehand.  Which device
needs to be resumed exactly to ensure ELD reception, the PCI one
or the codec?

Thanks,

Lukas
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