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

[Krzysztof Kozlowski <krzk@kernel.org>]

On 20/05/2026 14:30, Mark Brown wrote:
> 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.

Yes and that sounds a lot specific to particular controller, thus should
be implied by / deducible from the compatible.

Best regards,
Krzysztof