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

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

Hi Sourabh,

Thanks for updating the documentation..

On 23/01/25 5:12 pm, Sourabh Jain wrote:
> 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@linux.ibm.com>
> Cc: Brian King <brking@linux.ibm.com>
> Cc: Hari Bathini <hbathini@linux.ibm.com>
> Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
> Signed-off-by: Sourabh Jain <sourabhjain@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@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

"Support to add additional kernel parameters to FADump capture kernel" ?

> +   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.

The below details are more appropriate in "Sysfs/debugfs files:" section
with the details going under /sys/kernel/fadump/bootargs_append:

> +
> +  Command to Add Additional Kernel Parameters to Fadump:

Do those words really need to start with Uppercase?

> +  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.
> +

- Hari