Andi Kleen wrote: > Larry Finger <[EMAIL PROTECTED]> writes: > >> For those variants of BCM43xx cards that use 64-bit DMA, there is a >> requirement that all descriptor >> rings must be aligned on an 8K boundary and must fit within an 8K page. On >> the x86_64 architecture >> where the page size is 4K, I was getting addresses like 0x67AF000 when using >> dma_alloc_coherent >> calls. > > Normally x86-64 dma_alloc_coherent calls the buddy allocator which gives > you always naturally aligned blocks. But there is a fallback calling > into swiotlb and swiotlb uses best fit allocation which only guarantees > single page alignment. That is probably what you're seeing. > > My dma zone rework would remove that fallback case and should make it work. > >> From the description of the dma_pool_create and dma_pool_allocate routines, >> I thought they >> would fix my problems; however, even with a dma_pool_create(name, dev, 8192, >> 8192, 8192) call, I'm >> still getting 4K rather than 8K alignment, which results in DMA errors. > > They cannot give you more alignment than the underlying allocator. > >> Is there a bug in these routines, am I using them incorrectly, or do I have >> a misunderstanding of >> what it takes to get this kind of alignment? > > My suggestion as a short term workaround would be to first allocate > 8K using dma_alloc_coherent and if that has the wrong alignment get 16K > and align yourself. When the driver is loaded later that might be unreliable, > but near boot or with enough free memory using order 2 should usually work. > > With the dma zone rework that could be removed later.
I will be most interested in the dma zone rework; however, I now have the descriptors properly allocated merely by asking for 8K, just as I had thought it should work. I'm not quite sure what was wrong before, but I added a test to make certain that the alignment is OK just in case the problem comes back. Thanks for your response, Larry - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
