On 17. 04. 24 13:07, Pavel Hofman wrote: > I am considering implementation of multiple altsettings to f_uac2, so > that multiple combinations of channels and samplesizes can be offered to > the host. > > Configuration: > -------------- > * each altsetting for each direction should define > * channel mask > * samplesize > * hs_bint bInterval > * c_sync type (for capture only) > > > Perhaps the easiest config would be allowing lists for the existing > parameters (like the multiple samplerates were implemented). All the > list params would have to have the same number of items - initial check. > First values in the list would apply to altsetting 1, second to > altsetting 2 etc. > > Or the altsetting could be some structured configfs param - please is > there any recommended standard for structured configfs params? > > > Should the config also adjust the list of allowed samplerates for each > altsetting? Technically it makes sense as higher number of channels can > decrease the max samplerate, e.g. for via a TDM interface. If so, it > would need either the structured configuration or some "list of lists" > format. > > > Implementation: > --------------- > > Parameters could be turned to arrays of fixed predefined sizes, like the > p/s_srates. E.g. 5 max. altsettings in each direction would consume only > 4 * (5-1) + 3* (5-1) = 28 extra ints (excluding the samplerates config). > > Currently all descriptor structs are statically pre-allocated as there > are only two hard-coded altsettings. IMO the descriptors specific for > each altsetting could be allocated dynamically in a loop over all > none-zero alsettings. > > Please may I ask UAC2 gadget "stakeholders" for comments, suggestions, > recommendations, so that my eventual initial version was in some > generally acceptable direction? > This feature has coincidentally arisen in recent commits by Chris https://lore.kernel.org/lkml/c9928edb-8b2d-1948-40b8-c16e34cea3e2@xxxxxxxxxxx/T/ Maybe Takashi's commits to the midi gadget could be a way https://patchwork.kernel.org/project/alsa-devel/list/?series=769151&state=%2A&archive=both The midi gadget allows multiple configurations now, where configs are placed into a separate block.X configfs directory. That way the configfs recommendation to keep one value per item is adhered to and the configuration is nice and clean. This method would nicely allow various samplerate lists for each altsetting, without having to use some obscure list of lists. The f_uac2 tree config could have e.g. alt.1-X subdirs, to fit the altsetting ID. I am not sure the dot index not starting with 0 would be an issue. Now the question would be what to do with the existing (and the new params added by Chris) flat-structure parameters which apply to (the only one) altsetting 1. Maybe they could be used as defaults for the other altsettings for unspecified parameters? I very much appreciate any input, thank you all in advance. With regards, Pavel.
