Re: [PATCH 7/7] ASoC: SDCA: Add lock to serialise the Function initialisation

[Charles Keepax <ckeepax@opensource.cirrus.com>]

On Tue, Dec 09, 2025 at 12:20:41PM +0000, Pierre-Louis Bossart wrote:
> On 11/25/25 15:21, Charles Keepax wrote:
> > To avoid issues on some devices serialise the boot of each SDCA Function
> > from the others.
> 
> In theory all SDCA functions are independent, can you elaborate
> on what the problems might be?

How do I put this... hardware and firmware teams are really good
at always considering all the implications of the spec.

> I can certainly see that it's not efficient to try and
> download multiple firmware blobs over the same limited command
> or BPT/BRA channels, but I am not sure I see the dependencies
> between functions?

Generally the dependencies tend to come in from the implementation
not the specification. Whilst logically the functions are all
entirely independent, that is not necessarily how the hardware
will be implemented. I would guess it will be quite common for
the functions to be implemented on a shared back end.

We could implement this as a quirk instead and only apply the
lock for parts that require it, or we could force parts that need
it to use a customer driver. But, it seemed like a) others might
end up with similar requirements, b) the detriment of implementing
it for everyone is quite low, as you observe it's probably better
not to trying to kick off 4 BRA's at one time anyway.

So basically some parts will need it, a fully spec compliant part
would not. But as it has some practical benefits even for spec
compliant parts it seemed better to just add it and see where
that takes us.

Thanks,
Charles