On Tue, 10 Aug 2021 at 18:46, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > On Mon, Aug 02, 2021 at 04:23:57PM +0100, Lorenzo Pieralisi wrote: > > Add a __force attribute to the void* cast in acpi_os_map_iomem() > > to prevent sparse warnings. > > Err, no. These annotation are there for a reason and need to > be propagated instead. And independent of that a __force cast > without a comment explaining it is a complete no-go. The whole problem we are solving here is that ACPI, being based on x86, conflates MMIO mappings with memory mappings, and has been using the same underlying infrastructure for either. On arm64, this is not sufficient, given that the semantics of uncached memory vs device are different (the former permits unaligned accesses and clear cacheline instructions, but the latter doesn't). A recent optimization applied to memcpy() on arm64 (which now relies more on unaligned accesses for performance) has uncovered an issue where firmware tables being mapped non-cacheable by the ACPI core will end up using device mappings, which causes memcpy() to choke on their contents. So propagating the annotation makes no sense, as we are creating a memory mapping using the iomem primitive. I wouldn't object to a comment being added, but I think the context should have been obvious to anyone who had bothered to look at the entire series.
