Re: [PATCH 1/2] spi: dt-bindings: cdns,xspi: add sdma-io-width

[Mark Brown]

On Wed, May 20, 2026 at 02:16:21PM +0200, Krzysztof Kozlowski wrote:
> On 20/05/2026 13:48, Jisheng Zhang wrote:

> > If you mean "Why this cannot be deduced from the compatible?", I think
> > the slave dma port is part of the cdns xspi, so its io width belongs
> > to xSPI device property.
> > From another side, we have seen such property in other drivers such as
> > the reg-io-width for the dw spi DW_SPI_DR port io width.

> So you mean it depends on SPI device? Then why spi-peripheral-props is
> not applicable here?

That will be controller side, not device side.

> If this is not bus width, but DMA-something, is not really then SPI
> device dependent, but rather DMA controller limitation, so either
> deducible from compatible or something else is missing here.

My understanding is that this is a connection between the SPI and DMA
controllers so it's not as obvious as it could be which side of that
link should have the property, eg:

  https://www.cadence.com/content/dam/cadence-www/global/en_US/documents/tools/silicon-solutions/design-ip/controller-ip-qspi.pdf

shows a separate direct connection between the DMA controller and the
xSPI controller, the DMA controller isn't interacting with registers on
the CPU visible buses.  The width is probably a design time configurable
option on both sides of the link.

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