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

[Jisheng Zhang]

On Wed, May 20, 2026 at 09:09:55AM +0200, Krzysztof Kozlowski wrote:
> On 20/05/2026 01:38, Jisheng Zhang wrote:
> > On Fri, May 15, 2026 at 10:00:50AM +0200, Krzysztof Kozlowski wrote:
> >> On Mon, May 11, 2026 at 11:17:31AM +0800, Jisheng Zhang wrote:
> >>> The cdns xspi controller SDMA data port may support wider I/O width.
> >>> Wider I/O width can benefit performance. A simple test with QSPI nor
> >>> flash on one arm64 platform:
> >>>
> >>> 1 byte io width (default):
> >>>  # dd if=/dev/mtdblock0 of=/dev/null bs=8192 count=1000
> >>>  1000+0 records in
> >>>  1000+0 records out
> >>>  8192000 bytes (7.8MB) copied, 1.368735 seconds, 5.7MB/s
> >>>
> >>> 4 bytes io width:
> >>>  # dd if=/dev/mtdblock0 of=/dev/null bs=8192 count=1000
> >>>  1000+0 records in
> >>>  1000+0 records out
> >>>  8192000 bytes (7.8MB) copied, 1.088787 seconds, 7.2MB/s
> >>>
> >>> Improved by 26.3%!
> >>>
> >>> Add dt binding for sdma-io-width.
> >>>
> >>> Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxx>
> >>> ---
> >>>  Documentation/devicetree/bindings/spi/cdns,xspi.yaml | 6 ++++++
> >>>  1 file changed, 6 insertions(+)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/spi/cdns,xspi.yaml b/Documentation/devicetree/bindings/spi/cdns,xspi.yaml
> >>> index 38a5795589de..1fd4b6dfd417 100644
> >>> --- a/Documentation/devicetree/bindings/spi/cdns,xspi.yaml
> >>> +++ b/Documentation/devicetree/bindings/spi/cdns,xspi.yaml
> >>> @@ -40,6 +40,12 @@ properties:
> >>>    interrupts:
> >>>      maxItems: 1
> >>>  
> >>> +  sdma-io-width:
> >>> +    description: Slave DMA data port I/O width (in bytes)
> >>
> >> Waht is SDMA? What is Slave DMA? The same?
> >>
> >> Why this cannot be deduced from the compatible? DMA is fixed per
> >> platform and SDMA do not sound like SPI device (so slave in older
> >> terminology) property.
> > 
> > in cdns xspi, sdma == slave dma. It can be read by any master, such
> > as DMA engine or CPU. Its purpose and usage is similar as the data
> > reg in other spi controllers, e.g the DW_SPI_DR in dw spi. 
> 
> You did not really answer the questions.
> 

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.

Thanks