Re: [RFC PATCH 01/16] Documentation: driver: add SoundWire BRA description

[Charles Keepax <ckeepax@xxxxxxxxxxxxxxxxxxxxx>]

On Tue, Dec 19, 2023 at 06:08:15PM +0100, Pierre-Louis Bossart wrote:
> On 12/19/23 17:53, Mark Brown wrote:
> > On Tue, Dec 19, 2023 at 05:50:30PM +0100, Pierre-Louis Bossart wrote:
> >>> grep for regmap_.*async - cs_dsp.c is the upstream example in a driver,
> >>> or there's the rbtree cache sync code which uses a back door to go into
> >>> an async mode.  Basically just variants of all the normal regmap I/O
> >>> calls with a _complete() call you can use to wait for everything to
> >>> happen.  The implementation is a bit heavyweight since it was written to
> >>> work with fairly slow buses.
> > 
> >> I spent a fair amount of time this afternoon trying to understand the
> >> regmap_async parts, and I am not following where in the code there is an
> >> ordering requirement/enforcement between async and sync usages.
> > 
> > The only actual async implementation is SPI which processes things in
> > order of submission, the sync API wraps the async API.
> > 
> >> Also is this just me spacing out or there is no regmap_raw_read_async()?
> > 
> > Right, there was never any need.
> 
> ok. I am starting to think that we could have a new type of regmap, say
> "regmap-sdw-bra", where the use of write_raw_async() would rely on the
> send/wait bus primitives, and write_raw() would fallback to the regular
> read/write commands. We'd need a mutual exclusion to prevent parallel
> async/sync access to the same regmap.
> 
> In other words, "memory" areas that are used for firmware downloads
> would be moved to a different regmap with async capabilities and no
> caching support.

I would be a little inclined to say leave adding a regmap for a
follow up series, whether we add it to the existing regmap or add
a new one, or whatever, it should all sit happily on top of the
API being added in this series. Makes it a little more contained
to focus on one area at a time, and leave this series as adding
core support for BRA. But that said, if we really want to I don't
feel mega strongly on this one.

Thanks,
Charles