Dear Albert, Aneesh, Eric, > > We have a fundamental problem when it comes to invalidating an > > un-aligned buffer. Either you flush the boundary lines and corrupt your > > buffer at boundaries OR you invalidate without flushing and corrupt > > memory around your buffer. Both are not good! The only real solution is > > to have aligned buffers, if you want to have D-cache enabled and do DMA > > at the same time. > > Plus, there should not be *heavy* modifications; DMA engines tend to use > essentially two types of memory-resident objects: data buffers and > buffer descriptors. There's only a small handful of places in the driver > code to look at to find where these objects are allocated and how. > > So I stand by my opinion: since the cache invalidation routine should > only be called with cache-aligned objects, there is no requirement to > flush the first (resp. last) cache line in case of unaligned start > (resp.stop), and I don't want cache operations performed when they are > not required.
After considering all issues, any driver that does flush OR invalidate a cache line that it does not fully "own" is prone to cause problems. At flushing: some DMA might just have put data into the partial line. At invalidating: some Software might have put data, but the writeback had not occured. So both flush AND invalidate functions should check for this event and emit a proper warning on the console. My 2.7 cents... Reinhard _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
