[alsa-devel] DP MST audio support

[Dave Airlie]

Just to fill in the info on this one.

> We don't have Haswell Lenovo t440s atm, so could you share more info?
> - Dell U2410 should support both HDMI and DP input. But I guess it cannot
>  support DP MST, right?
> - Are you connecting this monitor a DP cable?
>  Which DDI port is used? DDI B, C or D?
> - Does audio fail after i915 enables DP MST?
> - Is patch "snd/hdmi: hack out haswell codec workaround" the only change
>  on audio driver side?

Yes its a DP SST input on the U2410, and I'm using that for the audio.

It's connected to the Lenovo dock with DP cable. The dock is an MST device.

The dock is connected to DDI C I think, and if the dock is operated in SST
mode audio works, but in MST mode audio fails. (operating the dock in SST
mode isn't useful though since only one of the multiple outputs works then).

>> > The graphics side patches are fairly trivial, also it would be good to
>> > get a good explaination of how the hw works,
>> >
>> > from what I can see devices get connections not pins on this hw, and I
>> > notice that I don't always get 3 devices, so I'm not sure if devices
>> > are a dynamic thing we should be reprobing on some signal.
>
> Do you mean 3 PCM devices here, like pcmC0D3p, pcmC0D7p, pcmC0D8p?
> Now the devices are not dynamic, a PCM device is created on each pin.
> It seems we need to revise this for DP MST, since a pin can be used to send
> up to 3 independent streams on Intel GPU which has 3 display pipelines.
>

No I mean the "Devices" from snd_hda_get_devices.

Dave.