[PATCH] powerpc: kdump: Reserve the existing TCE mappings left by the first kernel

Olof,
    Posting the modified patch based on your suggestion of reserving 
in-use TCE entries and use only available ones in the kdump boot. Please 
let me know your comments.

Thanks
Haren

During kdump boot, noticed some machines checkstop on dma protection 
fault for ongoing DMA left in the first kernel. Instead of initializing 
TCE entries in iommu_init() for the kdump boot, this patch fixes this 
issue by walking through the each TCE table and checks whether the 
entries are in use by the first kernel. If so, reserve those entries by 
setting the corresponding bit in tbl->it_map such that these entries 
will not be available for the kdump boot.

However it could be possible that all TCE entries might be used up due 
to the driver bug that does continuous mapping. This patch will make 
sure that minimum of 10 entries will be available such that kdump boot 
could be successful in some cases.

Signed-off-by: Haren Myneni <haren@us.ibm.com>