Re: [RFC PATCH 2/4] spi: cadence-xspi: add ACMD support for SPI NAND

[Miquel Raynal <miquel.raynal@bootlin.com>]

On 24/09/2026 at 19:55:58 +01, Mark Brown <broonie@kernel.org> wrote:

> On Wed, Sep 23, 2026 at 02:12:11PM +0800, Fei Xie wrote:
>
>> The difficulty is that the hardware ACMD sequencer needs the complete
>> multi-operation sequence to be described before it is started. For
>> example, the SPI NAND core currently submits PAGE READ, status polling
>> and READ CACHE as separate spi_mem_exec_op() calls. The STIG path can
>> execute those operations individually, while the ACMD hardware combines
>> them into one programmed sequence.
>
>> Would an SPI-mem operation-sequence interface be a reasonable direction
>> to explore? The NAND core could describe the ordered operations and
>> polling condition, and the controller could either execute the sequence
>> in hardware or fall back to the existing individual operations. This
>> would keep NAND-specific knowledge out of the controller driver.
>
> I think that makes sense, that mirrors some ideas people have had for
> optimising SPI mesages in general - submit the sequence to the driver to
> see if it can do it in one, falling back to just running individual
> operations if that doesn't work.  See spi_optimize_message().

The spi-mem operation-sequence interface seems very complex to handle
correctly IMHO. I fear such a solution would also require major rewrites
of the core. It is always hard to make fit hardware in code bases not
thought for them. Most of the time being spent in I/Os and wait states,
I am wondering how much would be saved by packing the commands. Do you
have benchmarks?

Thanks,
Miquèl