On Wed, 2009-11-18 at 15:38 +0100, Ralf Baechle wrote: > On Tue, Nov 17, 2009 at 11:03:47AM -0600, James Bottomley wrote: > > > On Virtually Indexed architectures (which don't do automatic alias > > resolution in their caches), we have to flush via the correct > > virtual address to prepare pages for DMA. On some architectures > > (like arm) we cannot prevent the CPU from doing data movein along > > the alias (and thus giving stale read data), so we not only have to > > introduce a flush API to push dirty cache lines out, but also an invalidate > > API to kill inconsistent cache lines that may have moved in before > > DMA changed the data > > The API looks right for MIPS and trivial to implement based on existing > code, so feel free to throw in my Ack on the generic parts. > > The new APIs deserve documentation in Documentation/cachetlb.txt. True (mutter, hate doing docs, mutter). How about this? James --- diff --git a/Documentation/cachetlb.txt b/Documentation/cachetlb.txt index da42ab4..7d1055c 100644 --- a/Documentation/cachetlb.txt +++ b/Documentation/cachetlb.txt @@ -377,3 +377,27 @@ maps this page at its virtual address. All the functionality of flush_icache_page can be implemented in flush_dcache_page and update_mmu_cache. In 2.7 the hope is to remove this interface completely. + +For machines where aliasing can be a problem, there exist two +additional APIs to handle I/O to vmap/vmalloc areas within the +kernel. These are areas that have two kernel mappings, one the regular +page offset map through which the page has likely been previously +accessed and the other, the new contiguous map in the kernel virtual +map area. This dual mapping sets up aliasing within the kernel and, +in particular since all kernel flushing goes through the offset map, +must be handled separately for I/O. to declare your architecture as +needing to use these functions, you must define +ARCH_HAS_FLUSH_KERNEL_DCACHE_PAGE in asm/cacheflush.h and add two API +helpers (usually as static inlines in cacheflush.h). The two new APIs +are: + + void flush_kernel_dcache_addr(void *addr) + Flush a single page through the vmap alias for addr. This is + usually executed prior to performing I/O on the page to make + sure the underlying physical page is up to date. + + void invalidate_kernel_dcache_addr(void *addr) + Invalidate the page after I/O has completed. This is necessary + on machines whose cache mechanisms might trigger cache movein + during I/O. If you can ensure architecturally that this movein + never occurs, this function can be empty on your architecture. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
