[PATCH v3 4/4] Documentation/powerpc/fadump: add additional parameter feature details

[Sourabh Jain]

Update the fadump document to include details about the fadump
additional parameter feature.

The document includes the following:
- Significance of the feature
- How to use it
- Feature restrictions

No functional changes are introduced.

Cc: Avnish Chouhan <avnish at linux.ibm.com>
Cc: Brian King <brking at linux.ibm.com>
Cc: Hari Bathini <hbathini at linux.ibm.com>
Cc: Madhavan Srinivasan <maddy at linux.ibm.com>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Mahesh Salgaonkar <mahesh at linux.ibm.com>
Signed-off-by: Sourabh Jain <sourabhjain at linux.ibm.com>
---
 Documentation/ABI/testing/sysfs-kernel-fadump |  3 ++-
 .../arch/powerpc/firmware-assisted-dump.rst   | 22 +++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-kernel-fadump b/Documentation/ABI/testing/sysfs-kernel-fadump
index 2f9daa7ca55b..b64b7622e6fc 100644
--- a/Documentation/ABI/testing/sysfs-kernel-fadump
+++ b/Documentation/ABI/testing/sysfs-kernel-fadump
@@ -55,4 +55,5 @@ Date:		May 2024
 Contact:	linuxppc-dev at lists.ozlabs.org
 Description:	read/write
 		This is a special sysfs file available to setup additional
-		parameters to be passed to capture kernel.
+		parameters to be passed to capture kernel. For HASH MMU it
+		is exported only if RMA size higher than 768MB.
diff --git a/Documentation/arch/powerpc/firmware-assisted-dump.rst b/Documentation/arch/powerpc/firmware-assisted-dump.rst
index 7e37aadd1f77..7e266e749cd5 100644
--- a/Documentation/arch/powerpc/firmware-assisted-dump.rst
+++ b/Documentation/arch/powerpc/firmware-assisted-dump.rst
@@ -120,6 +120,28 @@ to ensure that crash data is preserved to process later.
    e.g.
      # echo 1 > /sys/firmware/opal/mpipl/release_core
 
+-- Support for Additional Kernel Arguments in Fadump
+   Fadump has a feature that allows passing additional kernel arguments
+   to the fadump kernel. This feature was primarily designed to disable
+   kernel functionalities that are not required for the fadump kernel
+   and to reduce its memory footprint while collecting the dump.
+
+  Command to Add Additional Kernel Parameters to Fadump:
+  e.g.
+  # echo "nr_cpus=16" > /sys/kernel/fadump/bootargs_append
+
+  The above command is sufficient to add additional arguments to fadump.
+  An explicit service restart is not required.
+
+  Command to Retrieve the Additional Fadump Arguments:
+  e.g.
+  # cat /sys/kernel/fadump/bootargs_append
+
+Note: Additional kernel arguments for fadump with HASH MMU is only
+      supported if the RMA size is greater than 768 MB. If the RMA
+      size is less than 768 MB, the kernel does not export the
+      /sys/kernel/fadump/bootargs_append sysfs node.
+
 Implementation details:
 -----------------------
 
-- 
2.48.1