On Thu, 2012-08-30 at 15:49 -0500, Kumar Gala wrote: > On Aug 24, 2012, at 5:50 AM, 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: zone ZONE_DMA32 & 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_DMA32 > > to 2GB, also, we clear flag __GFP_DMA & __GFP_DMA32 and set __GFP_DMA32 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_DMA32, but devices which > > can DMA all the memory will not be affected by this limitation. > > > > Signed-off-by: Shaohui Xie <shaohui....@freescale.com> > > Signed-off-by: Mingkai Hu <mingkai...@freescale.com> > > Signed-off-by: Chen Yuanquan <b41...@freescale.com> > > --- > > changes for v2: > > 1. use a config option for using two zones (ZONE_DMA32 & ZONE_NORMAL) in > > freescale 64 bit kernel. > >
There must have been a misunderstanding. I think this should be a runtime choice, possibly by the platform code. Any reason that can't be done ? Also how does Intel do it ? Do they have iommu and ZONE_DMA32 co-exist ? Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev