Re: [PATCH 2/4] spi: spi-fsl-dspi: Use non-coherent memory for DMA

James Clark
2025-06-12T15:36:38Z

On 12/06/2025 3:36 pm, Vladimir Oltean wrote:
> On Thu, Jun 12, 2025 at 03:14:32PM +0100, James Clark wrote:
>>> FWIW, the XSPI FIFO performance should be higher.
>>
>> This leads me to realise a mistake in my original figures. My head was stuck
>> in target mode where we use DMA so I forgot to force DMA in host mode to run
>> the performance tests. The previous figures were all XSPI mode and the small
>> difference in performance could have been just down to the layout of the
>> code changing?
>>
>> Changing it to DMA mode gives figures that make much more sense:
>>
>> Coherent (4096 byte transfers): 6534 kbps
>> Non-coherent: 7347 kbps
>>
>> Coherent (16 byte transfers): 447 kbps
>> Non-coherent: 448 kbps
>>
>>
>> Just for comparison running the same test in XSPI mode:
>>
>> 4096 byte transfers: 2143 kbps
>> 16 byte transfers: 637 kbps
>
> So to be clear, the 'non-coherent' test was done just with patch 2
> applied, or also with 3?

The whole set, and then the non-coherent patch reverted.