On Thu, 2015-02-19 at 21:45 -0800, James Bottomley wrote: > Ben, this is legal by design. It was specifically designed for the > aic79xx SCSI card, but can be used for a variety of other reasons. The > aic79xx hardware problem was that the DMA engine could address the whole > of memory (it had two address modes, a 39 bit one and a 64 bit one) but > the script engine that runs the mailboxes only had a 32 bit activation > register (the activating write points at the physical address of the > script to begin executing). This meant that the scripts that run in > memory had to be in the first 4GB of physical memory, hence the split > mask. The DMA mask specifies that the card can transfer from anywhere > in physical memory, but the consistent_dma_mask says that the consistent > allocation used to get scripts memory must come from the lower 4GB.
Right, ok, it looks like it's easy enough to support with ZONE_DMA32, I'm testing patches to create it unconditionally on ppc64 (it used to depend on us using swiotlb on embedded platforms) and I'll shoot that upstream if it passes. Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
