On Thu, Jun 16, 2022 at 11:46:45AM +0200, Heiko Stübner wrote: > Without CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE and friends > dev_is_dma_coherent() will always return true otherwise the dma_coherent > attribute. Hence the "coherent" value for every system not managing things > will suddenly show as non-coherent where it showed as coherent before. Yes. > As we already have detection-points for non-coherent systems (zicbom > detection, t-head errata detection) No, we don't. There are plenty of reasons to support Zicbom without every having any non-coherent DMA periphals. Or just some non-coherent ones. So that alone is not a good indicator at all. The proper interface for that in DT-based setups i of_dma_is_coherent(), which looks at the dma-coherent DT property. And given that RISC-V started out as all coherent we need to follow the powerpc way (CONFIG_OF_DMA_DEFAULT_COHERENT) and default to coherent with an explcit propery for non-coherent devices, and not the arm/arm64 way where non-coherent is the default and coherent devices need the property.
