Hi,
((Sorry, re-sending because the first was rejected for not being plain
text))
(First up this is the first time I'm participating on a mailing list,
so sorry in advance if I'm doing something wrong).
Add support for Multi-stream transport for MSM chipsets that allow > a single instance of DP controller to send multiple streams. > >
This series has been validated on sa8775p ride platform using multiple >
MST dongles and also daisy chain method on both DP0 and DP1 upto 1080P.
> > With 4x4K monitors, due to lack of layer mixers that combination
will > not > work but this can be supported as well after some rework on
the DPU > side. > > In addition, SST was re-validated with all these
changes to ensure > there > were no regressions.
I have applied this patch series onto a near mainline 7.3 tree for the
Xiaomi Pad 6s Pro ("Sheng"), with SM8550. But with these patches
applied I don't have working audio, over USB-C to my (DisplayPort)
monitor, anymore. If I disable MST support on the monitor audio works
again. Debugging (using AI) reveals that the DP0 Jack is not reported as
connected anymore when connected to the monitor, with these patches
applied and MST enabled on the monitor. As shown, for example, by
amixer:
$ amixer -c 0 contents | grep -i -A8 -B3 -E 'hdmi|displayport|jack'
numid=208,iface=CARD,name='DP0 Jack'
; type=BOOLEAN,access=r-------,values=1
: values=off
With MST on the monitor disabled this outputs "values=on". The same is
also reflected by "pactl list cards" and "pactl list sinks" where
HDMI/DisplayPort is reported as "not available" with MST enabled (and
"available" when disabling MST).
(Again, suggested by AI) I also checked the ELD, which in both
cases (MST on and off on the monitor) is identical, including audio
information (like "speakers [0x1] FL/FR"). (Also, audio works both using
an AMD and an Intel based laptop, in which case I can also choose
whether to use "HDMI" or "HDMI 2" to switch audio output between two
monitors, in daisy chain).
So my foremost question is: should audio be supported in case of MST,
after applying these patches? Or is this possibly out of scope?
For clarity I would also like to note that without these patches
applied audio over DP does work as well, irrespective of MST being
on or off on the monitor (obviously always running as SST because of
missing kernel support). Which would make me believe that no audio
support in the same setup might be considered a regression?
Note that I do understand that me running a forked kernel on a
(by upstream) unsupported device might also lead to issues or require
changes for the fork. And that if audio does work with MST then this is
something the maintainers of the fork should, most likely, fix. But
from the cover letter and commit messages it is unclear to me whether
audio support should work and/or has been tested when MST is in use.
Kind regards,
Robert
