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

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. My observation is around
1700 TCE  entries are used on some systems (Ex: P4) at some point of
time during kdump boot and saving dump (either write into the disk or
sending to remote machine). Hence, this patch will make sure that
minimum of 2048 entries will be available such that kdump boot could be
successful in some cases.

Signed-off-by: Haren Myneni <haren@us.ibm.com>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/asm-powerpc/kdump.h b/include/asm-powerpc/kdump.h
index 5a5c3b5ab1e0..dc1574c945f8 100644
--- a/include/asm-powerpc/kdump.h
+++ b/include/asm-powerpc/kdump.h
@@ -15,6 +15,8 @@
 #define KDUMP_TRAMPOLINE_START  0x0100
 #define KDUMP_TRAMPOLINE_END    0x3000
 
+#define KDUMP_MIN_TCE_ENTRIES   2048
+
 #else /* !CONFIG_CRASH_DUMP */
 
 #define PHYSICAL_START  0x0