Re: [PATCH 2/3] spi: dt-bindings: cdns,xspi: add ACMD and internal DMA properties

[Conor Dooley <conor@kernel.org>]

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On Fri, Oct 30, 2026 at 09:57:36AM +0000, Nuno Sá wrote:
> On Thu, Oct 29, 2026 at 06:31:00PM +0000, Conor Dooley wrote:
> > On Thu, Oct 29, 2026 at 04:03:17PM +0000, Nuno Sá wrote:
> > > The Cadence xSPI controller supports an auto command (ACMD) mode where
> > > high level sequences (read, program, erase) are handled by the
> > > controller and data can be moved by its internal DMA. Whether ACMD can
> > > be used, and whether the internal DMA bus requester interface is wired,
> > > depends on how the IP is integrated (e.g. external SRAM, interconnect
> > > wiring) and cannot be discovered from the controller.
> > > 
> > > Add the cdns,has-acmd and cdns,has-internal-dma boolean properties to
> > > describe that. The internal DMA is only used by ACMD, so properly
> > > reflect that.
> > 
> > Why would these properties be needed? What the controller support surely
> > can be determined from the specific compatible for the SoC integration?
> 
> Alright, I'm more used to describe peripherals than this kind of IPs but
> I imagined that these being properties of the IP that would make sense
> to describe them in binding. Ok, but I sees this leaves the door

Basically the "rule" is "if it can be determined from the compatible, it
should be". Adding properties ends up with people having to figure out
exactly which features/quirks etc that their device needs and if things
are discovered after the fact it requires updating devicetrees that may
be bundled with firmware etc. Properties that are used to say that
something can do a feature should really only be used when the board
layout etc is what determines if the feature is available. That's much
more common for ADCs or w/e that are off-chip devices.

> open to just add properties in integrations that would not make sense
> and if we're going to have any compatible conditional kind of handling,
> I guess it makes them pointless.

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