hi, >> >> so,the problem is,can we use wback_inv instead of inv in pci_dma_sync_single >> when the direction is FROMDEVICE? I don't think so,but that would mean many >> current drivers are broken... > >If I understand this correctly, a writeback means only modified >cachelines (i.e. data cache lines with a dirty bit, like 'W', set) will >be written back to main memory. Since the driver never actually writes >to any of these buffers (and their contents are invalidated on the >pci_map_single()), nothing should ever be written back to main memory. >If this were not the case, you would surely see packet corruption as the >stale cachelines from a re-used buffer would be written back. I tend not >to think that it's just coincidence and that MIPS caches tend to be >small... Oh,yes,thank you. > >So, writeback-invalidate is not incorrect, but it's not efficient for >all platforms. Ralf explained to me that some CPUs cannot do indexed >invalidates separately from writebacks. > >I think all three (dma_cache_wback, dma_cache_wback_inv, >dma_cache_inv) of these calls should be implemented for all CPUs and >default to dma_cache_wback_inv() if not available. I can come up with a >patch if people agree (that wback_inv is a suitable replacement for >either _inv or _wback; MIPS-specific code than can be written to use >whatever is most optimal if present on that architecture... Why not? We have many different c-xxx.c for caches anyway. > >Thanks, >Will = = = = = = = = = = = = = = = = = = = = Best Regards --------------------------------------- Zhang Fuxin System Architecture Lab Institute of Computing Technology Chinese Academy of Sciences,China http://www.ict.ac.cn 2002-05-31
