Re: [PATCH v2 4/4] crypto: starfive - Add hash and HMAC support

[Christoph Hellwig]

On Thu, Feb 09, 2023 at 05:43:34PM +0800, Herbert Xu wrote:
> On Thu, Feb 09, 2023 at 09:33:06AM +0000, JiaJie Ho wrote:
> >
> > The DMA can only support 32-bit addressing.
> > So, I am copying everything in case kernel allocated memory region >32-bit for a user app.
> 
> Does your hardware support scatter-and-gather? If so you should
> at least allocate individual pages rather than one contiguous buffer.
> 
> Then you can allocate them on-demand rather than before-hand.
> 
> It would also be nice to not do the copy if the input you were
> given was in low memory (and contiguous if your hardware doesn't
> do SG).

All of that is done by the DMA API, or more specifically swiotlb and
does not need to be duplicated in individual drivers.