powerpc: Set crashkernel offset to mid of RMA region

[Hari Bathini]

On 28/01/22 3:34 pm, Sourabh Jain wrote:
> On large config LPARs (having 192 and more cores), Linux fails to boot
> due to insufficient memory in the first memblock. It is due to the
> memory reservation for the crash kernel which starts at 128MB offset of
> the first memblock. This memory reservation for the crash kernel doesn't
> leave enough space in the first memblock to accommodate other essential
> system resources.
> 
> The crash kernel start address was set to 128MB offset by default to
> ensure that the crash kernel get some memory below the RMA region which
> is used to be of size 256MB. But given that the RMA region size can be
> 512MB or more, setting the crash kernel offset to mid of RMA size will
> leave enough space for kernel to allocate memory for other system
> resources.
> 
> Since the above crash kernel offset change is only applicable to the LPAR
> platform, the LPAR feature detection is pushed before the crash kernel
> reservation. The rest of LPAR specific initialization will still
> be done during pseries_probe_fw_features as usual.
> 
> Signed-off-by: Sourabh Jain<sourabhjain at linux.ibm.com>
> Reported-and-tested-by: Abdul haleem<abdhalee at linux.vnet.ibm.com>
> 
> ---
>   arch/powerpc/kernel/rtas.c |  4 ++++
>   arch/powerpc/kexec/core.c  | 15 +++++++++++----
>   2 files changed, 15 insertions(+), 4 deletions(-)
> 
>   ---
>   Change in v3:
> 	Dropped 1st and 2nd patch from v2. 1st and 2nd patch from v2 patch
> 	series [1] try to discover 1T segment MMU feature support
> 	BEFORE boot CPU paca allocation ([1] describes why it is needed).
> 	MPE has posted a patch [2] that archives a similar objective by moving
> 	boot CPU paca allocation after mmu_early_init_devtree().
> 

> NOTE: This patch is dependent on the patch [2].
> 
> [1]https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20211018084434.217772-3-sourabhjain@linux.ibm.com/
> [2]https://lists.ozlabs.org/pipermail/linuxppc-dev/2022-January/239175.html

This dependency info must be captured somewhere within the changelog to
be useful.