[alsa-devel] DP1.2 MST audio support discussion

[Lin, Mengdong]

> -----Original Message-----
> From: David Henningsson [mailto:david.henningsson at canonical.com]
> Sent: Thursday, October 22, 2015 4:53 PM

[snip] 

> I'll try to explain my suggestion (which I believe Takashi's buying too) one
> more time then:
> 
> First, when a monitor is plugged in, we need to dynamically assign this
> monitor to five PCM devices. I believe this scheme will be best:
> 
> For a monitor at pin nid 0x05, dev index 0, it will prefer PCM 3.
> For a monitor at pin nid 0x06, dev index 0, it will prefer PCM 7.
> For a monitor at pin nid 0x07, dev index 0, it will prefer PCM 8.
> For a monitor at dev index 1 (any pin), it will prefer PCM 9.
> For a monitor at dev index 2 (any pin), it will prefer PCM 10.
> 
> For monitors at dev indices > 2 (can that happen?), or if the PCM is already
> assigned to something else, try PCMs in this order: 9, 10, 3, 7, 8.
> (Subject to discussion perhaps, I don't think the order matters too much,
> because conflicts will be rare in practice.)

Hi David,

Would you please clarify why PA needs such a fixed binding between PCM 3,7, 8 and pin 0x05,6,7?

And how will PA handle PCM 9,10 in a different way?
They are not bound to pins, and even not able to dev indexes. 
In practice, a platform will usually support either a DP port or a HDMI port from the Intel integrated GPU for cost consideration.
But theoretically i915 can use same device index on two different pins to connect monitors, e.g. pin 0x05, dev index 2 for one monitor and pin 0x06, dev index 2 for the other.

On Intel platforms, the max dev indices is 2. Not sure about Nvidia and AMD.

Thanks
Mengdong