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    [POWERPC] DMA 4GB boundary protection · 56997559
    Jake Moilanen 提交于
    There are many adapters which cannot handle DMAing across any 4 GB
    boundary.  For instance, the latest Emulex adapters.
    
    This normally is not an issue as firmware gives dma-windows under
    4gigs.  However, some of the new System-P boxes have dma-windows above
    4gigs, and this present a problem.
    
    During initialization of the IOMMU tables, the last entry at each 4GB
    boundary is marked as used.  Thus no mappings can cross the boundary.
    If a table ends at a 4GB boundary, the entry is not marked as used.
    
    A boot option to remove this 4GB protection is given w/ protect4gb=off.
    This exposes the potential issue for driver and hardware development
    purposes.
    Signed-off-by: NJake Moilanen <moilanen@austin.ibm.com>
    Acked-by: NOlof Johansson <olof@lixom.net>
    Signed-off-by: NPaul Mackerras <paulus@samba.org>
    56997559
iommu.c 17.4 KB