On Tue, Mar 04, 2003 at 06:11:48PM -0500, Dan Malek wrote: > Matt Porter wrote: > > > That means the ARM and MIPS implementations that use a > > bus_to_virt() on the dma_handle in *dma_sync_single are > > correct and our (performance killing) call to flush_dcache_all > > is unnecessary. > > Well, to be fair it seems this code has gone through a couple > of revisions since it was originally written. I suspect a "better > safe than sorry" approach was taken when changes were made. :-)
I figured that. :) > > If there are no objections, then I will commit to following > > patch to 2_4_devel and 2.5. The 2.5 pci_map_single/sync_single > > are horked up anyway for 4xx so that will get fixed too. > > OK, go for it. A couple of comments though......... > > > > #define CACHE_NWAYS 64 > > #define CACHE_NLINES 16 > > I made these #defines in the original code and I believe they were > set to values based upon the processor selection. When did they > change to 'worst case' and the most popular and most performance > challenged processors are paying the price for unnecessary cache > operations? I don't know the answer that. It happened before I first touched it. I simply upped the worst case to cover the larger 440 core dcache. > > -#ifdef CONFIG_NOT_COHERENT_CACHE > > - /* The bus_to_virt() can't be used here, in case dma_handle > > - * points to something that doesn't have the same cache attributes > > - * as the 1:1 mapped kernel memory. > > Ummm....this is a very important comment (not because I wrote it) :-) > On the 4xx and 8xx processors you can't use bus_to_virt() (unless we > are still calling iopa() and properly tracking all of the pages that > may be part of the DMA). Are we _sure_ we aren't using consistent_alloc()'ed > memory with these APIs? Yes, I completely understand the comment. :) As I said, the DMA API explicitly lists what memory can be passed to this family of API's. Memory allocated from pci_alloc_consistent cannot be passed in. Nor can ioremapped addresses. DaveM suggests another API be created to handle device to device transfers for 2.5+ for that specific case. I listed the types of allocated addresses that the API documentation explicitly mentions in the previous mail. Memory allocated via those methods will always be able to be converted back to a virtual address via bus_to_virt() because the allocations come from 1:1 kernel lowmem and are guaranteed to be contiguous. highmem is not a consideration since the *_single() family of calls is only usable on lowmem...*_page() would be used for highmem. Regards, -- Matt Porter porter at cox.net This is Linux Country. On a quiet night, you can hear Windows reboot. ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
