On Fri, 2012-07-20 at 20:21 +0800, Shaohui Xie wrote: > PowerPC platform only supports ZONE_DMA zone for 64bit kernel, so all the > memory will be put into this zone. If the memory size is greater than > the device's DMA capability and device uses dma_alloc_coherent to allocate > memory, it will get an address which is over the device's DMA addressing, > the device will fail. > > So we split the memory to two zones by adding a zone ZONE_NORMAL, since > we already allocate PCICSRBAR/PEXCSRBAR right below the 4G boundary (if the > lowest PCI address is above 4G), so we constrain the DMA zone ZONE_DMA > to 2GB, also, we clear the flag __GFP_DMA and set it only if the device's > dma_mask < total memory size. By doing this, devices which cannot DMA all > the memory will be limited to ZONE_DMA, but devices which can DMA all the > memory will not be affected by this limitation.
This is wrong. Don't you have an iommu do deal with those devices anyway ? What about swiotlb ? If you *really* need to honor 32 (or 31 even) bit DMAs, what you -may- want to do is create a ZONE_DMA32 like other architectures, do not hijack the historical ZONE_DMA. But even then, I'm dubious this is really needed. Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
