I would triple this for the steamOS case, which has an inversion of this problem (a playback device that has a coupled capture device for speaker management). Coupling PCM devices statically in the UCM file avoids a class of side effects that could occur if one tried to implement the same behavior with exec calls in Enable/DisableSequence. On Mon, Aug 28, 2023 at 11:35 AM Pierre-Louis Bossart < pierre-louis.bossart@xxxxxxxxxxxxxxx> wrote: > > > On 8/28/23 12:59, Curtis Malainey wrote: > > On Sat, Aug 26, 2023 at 4:28 AM Jaroslav Kysela <perex@xxxxxxxx> wrote: > >> > >> On 24. 08. 23 23:33, cujomalainey@xxxxxxxxxxxx wrote: > >>> From: Curtis Malainey <cujomalainey@xxxxxxxxxxxx> > >>> > >>> Sometimes userspace may want to use a reference channel to cancel echos > >>> when using video chat, this value identifies the device which carries > >>> that channel. > >> > >> The UCM modifier should be used for this - see "Echo Reference" > comments in > >> use-case.h. > >> > >> Note that this allows additional setup (in Sequences) for this stream. > >> > >> Jaroslav > > > > I was under the impression modifiers were state manipulators that > > acted upon existing devices/pcms and did not designate their own PCM. > > That is at least how we use them in CRAS. > > > > Are there any examples of how to designate a PCM? I don't see any > > modifiers at all in ucm-conf repo. > > I will second Curtis' request for clarifications. > > I naively thought that modifiers would be used to e.g. select a 'Deep > Buffer' output for low-power playback, or different capture streams > based on the needs of the applications. It's not uncommon for capture > applications to request different PCM streams for raw, AEC processed, > AEC+NS processed data. > > Echo reference is not really something that varies based on any > qualifiers. And specifically in the Chrome case we want userspace to > open the PCM echo reference device whenever the playback is used. So > it's not really a use-case dependent thing but more a way to express a > dependency between PCM devices. > -- Sincerely, Ethan Geller <http://ethangeller.com> LinkedIn <http://www.linkedin.com/pub/ethan-geller/3a/413/768>
