On 2/24/21 6:17 PM, Kai Vehmanen wrote:
Hey,
On Wed, 24 Feb 2021, Hui Wang wrote:
On 2/24/21 1:51 AM, Kai Vehmanen wrote:
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.
DP-MST is is reported per-pin, so basicly the interface can report display
connection status for "numpins*3" endpoints so that would be 9*3 on
Intel TGL systems.
However, this doesn't affect the converters. There is still four
converters, so 4 PCMs are enough to cover all possible combination of
plain DP/HDMI and DP-MST. User-space can query the ELD information to
learn the mapping from a PCM to a specific display (like e.g. Pulseaudio
does).
I sent a patch "ALSA: hda/proc - print DP-MST connections" to visualize
these a bit better in procfs output. I put example output in the commit:
https://lore.kernel.org/r/20201208185736.2877541-1-kai.vehmanen@xxxxxxxxxxxxxxx
Indeed, today I found a thunderbolt dock station which plays DP-MST hub
and I connected 2 monitors on it, they are 2 sub-devices belong to a
physical pin, and they are assigned different converters. And the procfs
output is very clear to show it.
Thanks,
Hui.
The existing driver provides a PCM for each pin, plus reserve two extra
PCMs for DP-MST. There's merit to this design as well, but arguably
the SOF approach is easier to understand on systems like TGL and ICL.
Br, Kai
