On Tue, Sep 21, 2021 at 10:20:07AM +0200, Christoph Hellwig wrote: > 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. But if the mapping request was rejected by devm_ioremap_resource() because of an attempt to map RAM, why we would get to dma_map_resource() at all? -- Sincerely yours, Mike.
