[PATCH] ALSA: hda/hdmi: let new platforms assign the pcm slot dynamically

[Hui Wang]

On 2/24/21 1:51 AM, Kai Vehmanen wrote:
> Hi,
>
> On Tue, 23 Feb 2021, Takashi Iwai wrote:
>
>> On Tue, 23 Feb 2021 17:25:23 +0100, Jaroslav Kysela wrote:
>>> A dumb question: Does TGL really support up to 11 separate displays or it's
>>> just to handle 11 connections and the number of maximal simultanenous
>>> connected displays is lower? In the later case, the dynamic allocation makes
>> That's the latter.  And, the fixed assignment was merely for
>> compatibility with legacy usage, and supposed to be 3 fixed ones or
>> so.  Extending to that high number wasn't intended when the mechanism
>> was introduced.  We should have noticed it at ICL support (which has
>> up to 6 devices).
> yes, exactly. The pins relate to physical ports. There are more pins now
> to cater for various DP-over-USB-C topologies (versus just native HDMI and
> DP ports). Most product have less physical ports connected, but on the HDA
> interface all pins are exposed. Each pin does provide functionality to
> query whether a display is connected to it, and whether the connected
> display has audio capability.
>
> The maximum number of concurrent displays is described as converters.
> On TGL this is 4.
If a physical port supports DP-MST, does the 3 connections on this 
physical port share a single converter? And each connection has an 
independent pcm,  maybe the driver should create pcm pool according to 
num_converter * 3.
>
> With SOF, we didn't have legacy userspace, so the HDMI/DP PCMs are already
> exposed differently and only a small number (3 or 4) of PCMs are created
> depending on hardware generation. Now the question is how we move
> snd-hda-intel to similar model with minimal distraction to existing
> user-space.

Let's do some change on TGL first, let us see if it will break some 
user-space apps, then we could evaluate how to handle it.

Thanks,

Hui.

> Br, Kai