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

David Laight
2025-06-13T15:56:42Z

On Tue, 10 Jun 2025 16:46:36 +0100
James Clark <james.clark@linaro.org> wrote:

> On 10/06/2025 4:15 pm, Frank Li wrote:
> > On Mon, Jun 09, 2025 at 04:32:39PM +0100, James Clark wrote:
> >> Using coherent memory here isn't functionally necessary.
> >> Because the
> >> change to use non-coherent memory isn't overly complex and only a few
> >> synchronization points are required, we might as well do it while fixing
> >> up some other DMA issues.
> >
> > Any beanfit by use on-coherent memory here?
> >
> > Frank
> >
>
> Presumably less cache maintenance traffic?

I bet it only helps when cache-coherent memory has to be uncached.
Otherwise the software cache operations are pretty much guaranteed
to be more expensive than the hardware ones.

David