[PATCH 9/9] powerpc/fadump: Update documentation about OPAL platform support

[Hari Bathini <hbathini@linux.ibm.com>]

With FADump support now available on both pseries and OPAL platforms,
update FADump documentation with these details. Also, update about
backup area and why it is used.

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
---
 Documentation/powerpc/firmware-assisted-dump.txt |  102 ++++++++++++++--------
 1 file changed, 64 insertions(+), 38 deletions(-)

diff --git a/Documentation/powerpc/firmware-assisted-dump.txt b/Documentation/powerpc/firmware-assisted-dump.txt
index 326f89c..eff9f38 100644
--- a/Documentation/powerpc/firmware-assisted-dump.txt
+++ b/Documentation/powerpc/firmware-assisted-dump.txt
@@ -70,7 +70,8 @@ as follows:
    normal.
 
 -- The freshly booted kernel will notice that there is a new
-   node (ibm,dump-kernel) in the device tree, indicating that
+   node (ibm,dump-kernel on PSeries or ibm,opal/dump/result-table
+   on OPAL platform) in the device tree, indicating that
    there is crash data available from a previous boot. During
    the early boot OS will reserve rest of the memory above
    boot memory size effectively booting with restricted memory
@@ -92,7 +93,20 @@ as follows:
 
 Please note that the firmware-assisted dump feature
 is only available on Power6 and above systems with recent
-firmware versions.
+firmware versions on PSeries (PowerVM) platform and Power9
+and above systems with recent firmware versions on PowerNV
+(OPAL) platform.
+
+To process dump on OPAL platform, additional meta data (PIR to
+Logical CPU map) from the crashing kernel is required. This info
+has to be backed up by the crashing kernel for capture kernel to
+use it in making sense of the register state data provided by the
+F/W. The start address of the area where this info is backed up
+is stored at the tail end of FADump crash info header. To indicate
+the presence of this additional meta data (backup info), the magic
+number field in FADump crash info header is overloaded as version
+identifier.
+
 
 Implementation details:
 ----------------------
@@ -108,56 +122,65 @@ that are run. If there is dump data, then the
 memory is held.
 
 If there is no waiting dump data, then only the memory required
-to hold CPU state, HPTE region, boot memory dump and elfcore
-header, is usually reserved at an offset greater than boot memory
-size (see Fig. 1). This area is *not* released: this region will
-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. Since this reserved
-memory area is used only after the system crash, there is no point in
-blocking this significant chunk of memory from production kernel.
-Hence, the implementation uses the Linux kernel's Contiguous Memory
-Allocator (CMA) for memory reservation if CMA is configured for kernel.
-With CMA reservation this memory will be available for applications to
-use it, while kernel is prevented from using it. With this FADump will
-still be able to capture all of the kernel memory and most of the user
-space memory except the user pages that were present in CMA region.
+to hold CPU state, HPTE region, boot memory dump, FADump header,
+elfcore header and backup area, is usually reserved at an offset
+greater than boot memory size (see Fig. 1). This area is *not*
+released: this region will 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.
+Since this reserved memory area is used only after the system crash,
+there is no point in blocking this significant chunk of memory from
+production kernel. Hence, the implementation uses the Linux kernel's
+Contiguous Memory Allocator (CMA) for memory reservation if CMA is
+configured for kernel. With CMA reservation this memory will be
+available for applications to use it, while kernel is prevented from
+using it. With this FADump will still be able to capture all of the
+kernel memory and most of the user space memory except the user pages
+that were present in CMA region.
 
   o Memory Reservation during first kernel
 
-  Low memory                                                Top of memory
-  0      boot memory size      |<--Reserved dump area --->|      |
-  |           |                |   Permanent Reservation  |      |
-  V           V                |   (Preserve area)        |      V
-  +-----------+----------/ /---+---+----+--------+---+----+------+
-  |           |                |CPU|HPTE|  DUMP  |HDR|ELF |      |
-  +-----------+----------/ /---+---+----+--------+---+----+------+
-        |                                   ^      ^
-        |                                   |      |
-        \                                   /      |
-         -----------------------------------     FADump Header
-          Boot memory content gets transferred   (meta area)
-          to reserved area by firmware at the
-          time of crash
-
+  Low memory                                                  Top of memory
+  0      boot memory size    |<---- Reserved dump area ---->|       |
+  |           |              |     Permanent Reservation    |       |
+  V           V              |       (Preserve area)        |       V
+  +-----------+--------/ /---+---+----+-------+-----+----+--+-------+
+  |           |              |///|////|  DUMP |HDR|/|ELF |//|       |
+  +-----------+--------/ /---+---+----+-------+-----+----+--+-------+
+        |                      ^    ^     ^      ^ |      ^^
+        |                      |    |     |      | |      ||
+        \                     CPU  HPTE   /      |  \    / Backup Info
+         ---------------------------------       |   ----
+      Boot memory content gets transferred       | Start address of
+      to reserved area by firmware at the        | Backup Info.
+      time of crash.                             |
+                                             FADump Header
+                                              (meta area)
                    Fig. 1
 
 
   o Memory Reservation during second kernel after crash
 
-  Low memory                                                Top of memory
-  0      boot memory size                                        |
-  |           |<------------- Reserved dump area --------------->|
-  V           V                |<---- Preserve area ----->|      V
-  +-----------+----------/ /---+---+----+--------+---+----+------+
-  |           |                |CPU|HPTE|  DUMP  |HDR|ELF |      |
-  +-----------+----------/ /---+---+----+--------+---+----+------+
+  Low memory                                                  Top of memory
+  0      boot memory size                                           |
+  |           |<--------------- Reserved dump area ---------------->|
+  V           V              |<----- Preserve area -------->|       |
+  +-----------+--------/ /---+---+----+-------+-----+----+--+-------+
+  |           |              |///|////|  DUMP |HDR|/|ELF |//|       |
+  +-----------+--------/ /---+---+----+-------+-----+----+--+-------+
         |                                              |
         V                                              V
    Used by second                                /proc/vmcore
    kernel to boot
                    Fig. 2
 
+        +---+
+        |///| -> Regions (CPU, HPTE, HDR extension & Backup area) marked
+        +---+    like this in the above figures are not always present
+                 For example, OPAL platform does not have CPU & HPTE regions
+                 while PSeries platform doesn't use Backup area currently.
+
+
 Currently the dump will be copied from /proc/vmcore to a new file upon
 user intervention. The dump data available through /proc/vmcore will be
 in ELF format. Hence the existing kdump infrastructure (kdump scripts)
@@ -289,7 +312,10 @@ TODO:
 	2. Reserve the area of predefined size (say PAGE_SIZE) for this
 	structure and have unused area as reserved (initialized to zero)
 	for future field additions.
+
    The advantage of approach 1 over 2 is we don't need to reserve extra space.
+   Using approach 1 to provide additional meta data on OPAL platform while
+   overloading magic number field as version identifier for version tracking.
 ---
 Author: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
 This document is based on the original documentation written for phyp