[alsa-devel] i915, HDMI/DP audio with multiple monitors

[Ville Syrjälä]

On Tue, Sep 11, 2018 at 03:50:13PM +0200, Bruno Prémont wrote:
> Hi,
> 
> I have a system with multiple monitors and would like to send
> notification sounds to the monitor on which corresponding
> window is visible.
> 
> For a workstation and a tiny computer things look different:
> - workstation (Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz):
>  00:02.0 VGA compatible controller [0300]: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controller [8086:0412] (rev 06)
>  00:03.0 Audio device [0403]: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor HD Audio Controller [8086:0c0c] (rev 06)
>  00:1b.0 Audio device [0403]: Intel Corporation 8 Series/C220 Series Chipset High Definition Audio Controller [8086:8c20] (rev 04)
> 
>  Here alsa show me two cards:
>  - HDA Intel PCH (Realtek ALC671)
>  - HDA Intel HDMI (Intel Generic)
> 
>  **** List of PLAYBACK Hardware Devices ****
>  card 0: HDMI [HDA Intel HDMI], device 3: Generic Digital [Generic Digital]
>    Subdevices: 1/1
>    Subdevice #0: subdevice #0

There should normally be multiple HDMI devices (one for each HDMI/DP
connector more or less). Eg. my hsw shows:

card 0: HDMI [HDA Intel HDMI], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: HDMI [HDA Intel HDMI], device 7: HDMI 1 [HDMI 1]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Looking at the hda_codec.c we see:
 static int audio_idx[HDA_PCM_NTYPES][5] = {
...
        [HDA_PCM_TYPE_HDMI]  = { 3, 7, 8, 9, -1 },

So you always get those device numbers, but I don't see an immediate
relationship between those and the pin numbers (which do have some
kind of relationship with the HDMI/DP port). I guess if they always
get registered in order of the pin numbers then those would translate
to 3 == port B, 7 == port C, etc. And after that the problem is figuring
out which port is related to which connector, for which we have nothing
at the moment.

I suppose the ideal solution might be to have a sysfs symlink (or
something) to connect the two together.

But then there's MST where I think the pcm device correlates with the
crtc rather than the connector. Maybe. I can't remember anymore, and
I'm not sure it even works (I've recently heard people saying it
doesn't).

>  card 1: PCH [HDA Intel PCH], device 0: ALC671 Analog [ALC671 Analog]
>    Subdevices: 1/1
>    Subdevice #0: subdevice #0
> 
> 
> - tiny computer (Intel(R) Core(TM) i5-6500T CPU @ 2.50GHz):
>  00:02.0 VGA compatible controller [0300]: Intel Corporation HD Graphics 530 [8086:1912] (rev 06)
>  00:1f.3 Audio device [0403]: Intel Corporation Sunrise Point-H HD Audio [8086:a170] (rev 31)
> 
>  Here alsa shows a single card:
>  - HDA Intel PCH (Realtek ALC671)
> 
>  **** List of PLAYBACK Hardware Devices ****
>  card 0: PCH [HDA Intel PCH], device 0: ALC671 Analog [ALC671 Analog]
>    Subdevices: 1/1
>    Subdevice #0: subdevice #0
>  card 0: PCH [HDA Intel PCH], device 3: Generic Digital [Generic Digital]
>    Subdevices: 1/1
>    Subdevice #0: subdevice #0
> 
> 
> How can I determine/set to which monitor the sound should go, and preferably send
> different sounds to both monitors at same time?
> 
> 
> Cheers,
> Bruno
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-- 
Ville Syrjälä
Intel