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

[Krzysztof Kozlowski <krzk@kernel.org>]

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@kernel.org>
>>> ---
>>>  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.

Best regards,
Krzysztof