[PATCH v4 2/7] powerpc/fadump: Update documentation to reflect the metadata region movement.

[Mahesh J Salgaonkar]

From: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>

Metadata region that holds fadump header and ELF header is now placed at
the start of reserved memory area. Update the documentation accordingly

Signed-off-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
---
 Documentation/powerpc/firmware-assisted-dump.txt |   33 ++++++++++++++--------
 1 file changed, 21 insertions(+), 12 deletions(-)

diff --git a/Documentation/powerpc/firmware-assisted-dump.txt b/Documentation/powerpc/firmware-assisted-dump.txt
index bdd344aa18d9..30b32f879219 100644
--- a/Documentation/powerpc/firmware-assisted-dump.txt
+++ b/Documentation/powerpc/firmware-assisted-dump.txt
@@ -115,17 +115,26 @@ be kept permanently reserved, so that it can act as a receptacle
 for a copy of the boot memory content in addition to CPU state
 and HPTE region, in the case a crash does occur.
 
+The first kernel, during fadump registration, prepares ELF core header
+that contains necessary information for the coredump of the 1st kernel
+which includes its physical memory layout. This ELF header and some more
+additional data is stored in the area called metadata region at the start
+of the reserved memory area. The implementation maintains the compatibility
+between production/capture kernels irrespective of their kernel versions.
+Both combination older/newer and newer/older works fine.
+
   o Memory Reservation during first kernel
 
   Low memory                                         Top of memory
   0      boot memory size                                       |
   |           |                |<--Reserved dump area -->|      |
   V           V                |   Permanent Reservation |      V
-  +-----------+----------/ /---+---+----+-----------+----+------+
-  |           |                |CPU|HPTE|  DUMP     |ELF |      |
-  +-----------+----------/ /---+---+----+-----------+----+------+
-        |                                           ^
-        |                                           |
+  +-----------+----------/ /---+----+---+----+-----------+------+
+  |           |                |ELF |CPU|HPTE|  DUMP     |      |
+  +-----------+---------/ /----+----+---+----+-----------+------+
+        |                        ^                  ^
+        |                        |                  |
+        |                metadata region            |
         \                                           /
          -------------------------------------------
           Boot memory content gets transferred to
@@ -137,14 +146,14 @@ and HPTE region, in the case a crash does occur.
 
   Low memory                                        Top of memory
   0      boot memory size                                       |
-  |           |<------------- Reserved dump area ----------- -->|
+  |           |<------------- Reserved dump area -------------->|
   V           V                                                 V
-  +-----------+----------/ /---+---+----+-----------+----+------+
-  |           |                |CPU|HPTE|  DUMP     |ELF |      |
-  +-----------+----------/ /---+---+----+-----------+----+------+
-        |                                              |
-        V                                              V
-   Used by second                                /proc/vmcore
+  +-----------+----------/ /---+----+----+---------------+------+
+  |           |                |ELF |CPU|HPTE|  DUMP     |      |
+  +-----------+----------/ /---+----+----+---------------+------+
+        |                         |
+        V                         V
+   Used by second             /proc/vmcore
    kernel to boot
                    Fig. 2