Hi Reinhard, On 05/08/2011 13:23, Reinhard Meyer wrote: > 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.
Fully agreed. > My 2.7 cents... > Reinhard Amicalement, -- Albert. _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
