From: Stephen Hemminger <[EMAIL PROTECTED]> Date: Wed, 6 Dec 2006 10:16:44 -0800
> I think it is really only an issue for drivers that turn on HIGH_DMA > and have limited mask values. The majority of drivers either only handle > 32 bit (!HIGH_DMA) or do full 64 bit mapping. I don't know the details > of how we manage IOMMU, but doesn't mapping always work for those drivers. > > That just leaves devices with odd size mask values that need to be > handle mapping errors. Not true. On platforms such as sparc64 the IOMMU is used for all DMA mappings, no matter what, because only IOMMU based mappings can do prefetching and write-combining in the PCI controller. The problem with just silently dropping packets that can't get DMA mapped is that you're going to drop a very large sequence of these while the IOMMU is out of space, and that to me looks like a bad quality of implementation decision. The IOMMU layer really needs a way to callback the driver to tell it when space is available, or something similar. FWIW, Solaris handles this by blocking when the IOMMU is out of space since under Solaris even interrupt contexts can block (via interrupt threads). - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
