Re: [PATCH 0/8] dma-mapping: migrate to physical address-based API

Marek Szyprowski
2025-06-27T13:44:18Z

On 25.06.2025 15:18, Leon Romanovsky wrote:
> This series refactors the DMA mapping to use physical addresses
> as the primary interface instead of page+offset parameters. This
> change aligns the DMA API with the underlying hardware reality where
> DMA operations work with physical addresses, not page structures.
>
> The series consists of 8 patches that progressively convert the DMA
> mapping infrastructure from page-based to physical address-based APIs:
>
> The series maintains backward compatibility by keeping the old
> page-based API as wrapper functions around the new physical
> address-based implementations.

Thanks for this rework! I assume that the next step is to add map_phys
callback also to the dma_map_ops and teach various dma-mapping providers
to use it to avoid more phys-to-page-to-phys conversions.

I only wonder if this newly introduced dma_map_phys()/dma_unmap_phys()
API is also suitable for the recently discussed PCI P2P DMA? While
adding a new API maybe we should take this into account? My main concern
is the lack of the source phys addr passed to the dma_unmap_phys()
function and I'm aware that this might complicate a bit code conversion
from old dma_map/unmap_page() API.

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland