Re: [PATCH v5 5/6] ASoC: codecs: wcd938x: add mux control support for hp audio mux

[Srinivas Kandagatla]

Thanks Peter,

On 25/03/2025 20:13, Peter Rosin wrote:
> Hi!
>
> 2025-03-25 at 19:04, Srinivas Kandagatla wrote:
> > I wish we could be taken care in mux-core or even in the deselect api
>
> It is not easily done. A mux is a shared resource. How can the mux core
> know if it is consumer A or consumer B that deselects the mux if both
> ignore failures when calling select? Mux select is backed by a semaphore
> and there is no guarantee that a consumer selects/deselects from the
> same thread or anything like that. The onus is on the consumer to get
> this right and only deselect when select is successful.

Should deselect fail if there was no previous mux selected?

> I believe the documentation is clear on this topic: "do not call
> mux_control_deselect() if mux_control_select() fails".

True, the documentation is pretty clear about this behavior.
> One thing can be done from the mux core, and that is to provide a new
> API where consumers get a mux that is exclusive so that the consumer
> can call select/deselect without involving a lock in the core. There
> need not even be a requirement to call deselect between selects in that
> case. Such an API is what many consumers want, I think, but it is of
> course not really compatible with the existing API, which is totally
> focused on the need to share a mux among multiple consumers.
exclusive apis would simplify the consumer side of code for sure.

> And, of course, someone has to do it.

Yes, I can give it a go and see how it will turn out.

--srini
> Cheers,
> Peter