Re: [PATCH 0/2] ASoC: cs35l56/57/62/63: Use the correct SoundWire DP for feedback

[Richard Fitzgerald <rf@opensource.cirrus.com>]

On 05/10/2026 7:33 pm, Pierre-Louis Bossart wrote:
> On 10/5/26 17:52, Richard Fitzgerald wrote:
>> The amp feedback path (AEC) was incorrectly using SoundWire DP3.
>> The firmware outputs SDCA OT25 feedback on DP4. DP3 is reserved for
>> SDCA companion amp.
>>
>> This series adds a DAI for OT25 and switches the sdw machine driver
>> to use the new DAI for the feedback path.
> 
> Is there any merit in keeping this DP3 exposed as a capture DAI, if
> indeed it's intended to be a side connection for a companion chip?

I kept this patch to a minimum because it is a Fixes: so it must apply
to older kernels.

However, you are correct. DP3 isn't used now. Not even on companion amp. 
DP3 is a companion output from the amp (SDCA OT127), but Cirrus
companion amp goes codec->amp so uses DP1 on the amp.

When the driver was being written the SDCA spec and firmware behavior
were not fully defined so pairing of the symmetrical DP1+DP3
(for play+capture) was carried forward from previous amps. But SDCA
doesn't provide any sort of UCM capability - widgets on the device have
defined, fixed functionality that has to be preconfigured by the
firmware to match what SDCA needs. Ultimately DP4 was more suitable for
OT25. DP4 also works for loopback testing.

Removing DP3 would also solve some other problems that the driver and
firmware are both "owning" the registers. We originally attempted to
sync this up, then gave up on that complexity and overwrite the register
settings the firmware made.