On Mon, Sep 20, 2021 at 11:57:58AM +0100, Catalin Marinas wrote: > > As this WARN_ON(pfn_valid()) is only present in dma_map_resource() it's > > probably safe to drop it entirely. > > I agree, we should drop it. IIUC dma_map_resource() does not create any > kernel mapping to cause problems with attribute aliasing. You'd need a > prior devm_ioremap_resource() if you want access to that range from the > CPU side. For arm64 at least, the latter ends up with a > pfn_is_map_memory() check. It doesn't create any new mappings. The only real issue is that it does the wrong thing for RAM in a way that might not be noticed on simple (x86/PC) platforms.
