On Wed, Aug 11, 2021 at 12:40:28PM +0200, Ard Biesheuvel wrote: > 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. I can add a comment and respin. Basically a __force attribute is added to ignore a sparse warning that's been ignored for aeons anyway - I will add the rationale above. drivers/acpi/osl.c:379:17: warning: cast removes address space '__iomem' of expression
