Re: [PATCH] riscv: select DMA_DIRECT_REMAP by RISCV_ISA_SVPBMT and ERRATA_THEAD_MAE

Christoph Hellwig
2025-01-17T09:58:45Z

On Fri, Jan 17, 2025 at 11:38:47AM +0300, Sergey Matyukevich wrote:
> > Please explain what this is supposed to solve, because the above
> > explanation dosn't make any sense. DMA_DIRECT_REMAP is one
> > of the implementations supporting dma coherent allocatiosn for
> > non-coherent devices. So selecting it from something that
> > just keyes off support for an extension, but not the dma
> > implementation is wrong.
>
> Now DMA_DIRECT_REMAP is selected either by Zicbom (standard) or XTheadCmo
> (vendor) RISC-V extensions.

Because they need DMA_DIRECT_REMAP to implement DMA coherent.

> However neither of them can help to implement
> DMA_DIRECT_REMAP on RISC-V. So selection of DMA_DIRECT_REMAP has been
> moved in Kconfigs to Svpbmt and XTheadMae extensions.

But Svpbmt does not imply that you even need DMA_DIRECT_REMAP.

Are you tying to solve a problem here? If so can you explain it?