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

[Christoph Hellwig]

On Thu, Jan 16, 2025 at 08:29:35PM +0300, Sergey Matyukevich wrote:
> Select DMA_DIRECT_REMAP for the RISC-V extensions that allow to set
> page-based memory types in PTEs according to the requested DMA
> attributes. This is the purpose of Svpbmt or XTheadMae extensions.
> Zicbom or XTheadCmo serve a different purpose, providing instructions
> to flush/invalidate cache blocks.

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.