On Fri, 2008-10-10 at 14:46 +1100, Benjamin Herrenschmidt wrote: > > > A virtual address will typically be needed to perform the flush; why > > > pass the bus address? > > > Because it is a sync API. You want to make sure that a physical memory > > area is in sync with the caches, not the virtual address. This > > distinction can become important in the event where the page is mapped > > multiple times in the memory and the architecture does not take care of > > synchronizing the multiple mapping, the dma_mapping_ops code should be > > able to synchronize the multiple mapping. In most case it would be easy > > of course to go from virtual address to the page address, but not if the > > page is in high memory ... > > Well, not really. IE, you are right that a dma_addr_t or a struct page > is the way to go but for the wrong reasons :-) > > All mappings should be coherent. The powerpc architecture is pretty > strict with that. The only known violation is the instruction cache on > 44x but that's irrelevant to your problem. > > Thus, -any- virtual address will do. Good! That certainly simplify the code.
> However, you may not have a virtual address. You may get into a > situation where the page isn't in the linear mapping and needs to be > kmap'ed for the sync to happen. > > Now, using PCI_DRAM_OFFSET in bus_to_page() is incorrect here with > Becky's new set of changes. You need to get the offset properly using > the accessor she provides (I don't have the name off the top of my > head). > Totally agree with that. In the last set of patch I committed (which I need to re-commit because I need to use vmalloc in dma-noncoherent.c) I removed most of the reference to PCI_DRAM_OFFSET. The only reference to it remaining is in virt_to_bus which is called by dma_cache_sync. I did not see an accessor that can be used in dma-mapping.h (the accessor API I have seen is private to dma.c and dma-noncoherent.c), I would be happy to use it if there really is one though. I could add another 2 APIs to dma_mapping_ops which converts a page to/from its bus address, what do you think? Remi _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
