Hello everyone,
I have pushed a PipeWire / WirePlumber update in gerrit [1] to be
included in master for the next AGL release (LL). In this email I want
to give an overview of what has changed, so that you have a starting
point to work with it until the documentation is fully up-to-date (WIP).
PipeWire
---
PipeWire has been updated to version 0.3.25+. I plan to update it again
to a release version (perhaps .26 or .27) before the final freeze for LL.
Support for embedded devices has been improved in this release. Devices
like the ones found in the iMX family of SoCs should now work well
without additional patches. For some devices, though, there may be a
need for tweaking things. Many configuration options exist and are
documented in
https://gitlab.freedesktop.org/pipewire/pipewire/-/wikis/Config-ALSA
However, bear in mind that this wiki page applies to pipewire's default
session manager and NOT to wireplumber. The equivalent file for tweaking
these options in wireplumber is
/etc/wireplumber/config.lua.d/30-alsa-monitor.lua
I will provide further documentation on this topic as soon as possible.
WirePlumber
---
WirePlumber has been updated to the git master version (0.3.70+, to be
released as 0.4.0)
Among other things, this version introduces Lua-based configuration and
scripting.
The default configuration file is now /etc/wireplumber/config.lua,
which can be split into several files in /etc/wireplumber/config.lua.d/
All files are interpreted in the same context (so variables from one
file are accessible in the next ones) and so it is possible to override
options in other files without touching the default ones.
The purpose of this configuration file is to load modules and scripts in
wireplumber and activate them. It cannot do anything else, as it does
not have access to the full lua API that wireplumber implements.
Apart from configuration, there are also scripts. Scripts have access to
the full API and implement the logic of wireplumber (policy, device
loading, etc...). The upstream scripts are installed in
/usr/share/wireplumber/scripts and it is possible to override them by
installing equivalents in /etc/wireplumber/scripts/. Scripts in /etc
will shadow the scripts in /usr that have the same name, so if you wish
to experiment changing a script, it is advised that you copy it first to
/etc and modify it there.
Additionally, it is possible to execute scripts standalone on the
command line in order to test them or to implement tools to do things
with pipewire. These scripts are executed with /usr/bin/wpexec. You can
see examples of such standalone scripts in
https://gitlab.freedesktop.org/pipewire/wireplumber/-/tree/master/tests/examples
Tools
---
PipeWire tools are now named differently and they all have the 'pw-'
prefix in their names. All of these tools are now packaged in a separate
package and are only available in the image if you build with the
'agl-devel' feature.
pw-cli is the main tool for interacting with pipewire.
There is also pw-dump, which dumps all objects in a big JSON. The output
of this tool is very useful to include in bug reports. It is also
suitable for implementing scripts that parse information with jq.
pw-dot is another useful debug tool that dumps the objects in a dot
graph for easy visualization
pw-cat / pw-play / pw-record: This is a set of tools similar to
aplay/arecord, for simple audio operations
pw-top: This is a performance measurement tool that shows realtime
timing information about the audio pipeline. Before running this tool,
you will need to uncomment the loading of "libpipewire-module-profiler"
in /etc/pipewire/pipewire.conf and restart pipewire.
Wireplumber also has a tool called wpctl. This is available always (not
only on 'agl-devel') and replaces the old wireplumber-cli. It allows
inspecting the devices, choosing which source & sink are the default
ones and provides the equivalent of the mixer on the command line.
Try "wpctl status" and "wpctl help" to get started with it.
Mixer
---
The mixer app has been updated to work with the latest underlying APIs.
It also now exposes a "Master Capture" volume, that controls the
microphone volume, and it also exposes again all the role-specific volumes.
Bluetooth
---
Bluetooth audio using bluez and ofono is now provided by PipeWire
natively instead of relying on bluez-alsa hacks. Audio from a mobile
phone is also now properly routed through the "Communication" role
endpoint and adheres to the policy.
bluez-alsa should no longer be present in the images.
Policy
---
WirePlumber policy is now fully scripted in lua and can be more easily
adapted to suit your needs.
For AGL, wireplumber exposes a set of "Endpoints" that correspond to
media roles, like before. When playing audio, clients are routed through
those endpoints and adhere to rules, based on the configured priority of
the roles. The configuration for this is in
/etc/wireplumber/config.lua.d/10-default-policy.lua
In order for clients to be considered for this policy, they must have
the "media.role" property set on them. In gstreamer this is done by
adding "stream-properties=p,media.role=<role>" to the properties of
pipewiresink. In pw-play, there is the --media-role command line option.
If the media.role is not set, the client is considered for linking with
the standard desktop policy, which is also enabled. This will link the
client directly to the device and it will not be subject to the rules. I
plan to make this configurable in another update, so that such usage can
be prohibited.
Unlike before, with this update it is possible to have different actions
per role. For instance, for the Multimedia role, it is not allowed to
have more than one client playing at a time, so only the last one is
linked and the others are corked. For other roles, it is allowed to mix
sounds of the same role while sounds of lower priority roles are corked.
In another update I am also planning to add the option to "duck" the
volume of another role instead of corking it.
Security
---
Both PipeWire and WirePlumber are now executed as a separate 'pipewire'
user. The socket for pipewire is placed in /run/pipewire/ and is
accessible by all other users.
For use with AGL's current app framework, there is a pipewire module
that allows by default full access to clients that have the "System"
SMACK label and restricts all other clients.
Then, there is a wireplumber access policy script that grants full
access again to clients that have a SMACK label starting with
"User::App::". This will be changed in another update. The plan is to
keep such clients still restricted, based on what their role is, and
only allow them to use specific pipewire objects.
Known Issues
---
At the time of writing, I am aware of 3 issues so far.
1. An unresolved issue from the past: When corking clients, these
clients are not fully aware about the fact that they have been corked.
Also, when the clients are paused, the session manager is not fully
aware about the fact that they are paused. This can lead to bad behavior
if clients are paused instead of stopped. This is discussed in [2]
2. When pausing a gstreamer pipewiresink for too long and then resuming
it again, it may end up in a situation where it doesn't play. This is
reported in [3].
3. On the H3 reference hardware board, a microphone connected on the
'mic' port does not sound right. The audio is garbled. This seems to be
some strange driver configuration / latency issue. It works under
certain conditions with plain alsa (tried with gstreamer alsasrc), but
not with pipewire. I will investigate this further.
Best regards,
George
[1]. https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/26094
[2]. https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/205
[3]. https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/1048
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