Re: [PATCH 1/2] firmware: cs_dsp: Remove async regmap writes

[Mark Brown]

On Tue, Feb 25, 2025 at 01:18:42PM +0000, Richard Fitzgerald wrote:

> The async writes are a 12-year-old workaround for inefficiency of
> synchronous writes in the SPI subsystem. The SPI subsystem has since
> been changed to avoid the overheads, so this workaround should not be
> necessary.

That wasn't really the issue, it was that on systems with low numbers of
slower cores (especially single core but there were some dual core
systems too) there was a surprisingly low threashold where it was useful
to overlap the marshalling of data to send to the device with
transmitting already marshalled data.  SMP adds locking requirements
which loose a lot of the gains, and it's controller dependent where the
cuttoff points for interrupts and/or DMA are.

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