Documentation/powerpc/fadump: add additional parameter feature details

JIRA: https://issues.redhat.com/browse/RHEL-70827

commit 61c403b
Author: Sourabh Jain <sourabhjain@linux.ibm.com>
Date:   Thu Jan 23 17:12:54 2025 +0530

    Documentation/powerpc/fadump: add additional parameter feature details

    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.

    Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
    Reviewed-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
    Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
    Link: https://patch.msgid.link/20250123114254.200527-5-sourabhjain@linux.ibm.com

Signed-off-by: Mamatha Inamdar <minamdar@redhat.com>

Author: Mamatha Inamdar

Documentation/ABI/testing/sysfs-kernel-fadump

@@ -55,4 +55,5 @@ Date:		May 2024
 Contact:	linuxppc-dev@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.

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:
 -----------------------