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

[Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>]

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.