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

Arnd Bergmann
2025-06-12T15:40:55Z

On Thu, Jun 12, 2025, at 16:14, James Clark wrote:
> On 12/06/2025 12:15 pm, Vladimir Oltean wrote:
> 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

Ok, good. The improvement from the patch is less than I had hoped
for, but it does sound like at least it doesn't get worse for
small transfers.

Arnd