On Sun, Sep 22, 2024 at 10:06:59AM +0000, Vladimir Kondratiev wrote: > This is the whole point - there are platforms where you can't allocate 32-bit > dma-able memory. Ugg. They will be broke for all kinds of devices (plug in PCIe devices IP IP blocks). > Unless there's IOMMU or some platform specific tricks, > DMA address is same as physical address. Well, that's where the usual platform specific trick is, as the platforms with high DRAM either have a mapping between physical and DMA range (see the dma_ranges concept in the DMA and OF code) or a mirror of the higher addresses. Or very rarely (e.g. sparc) a required IOMMU that is always used.
