[PATCH v1 2/2] powerpc: add support for Kexec HandOver (KHO)

[Sourabh Jain <sourabhjain@linux.ibm.com>]

Add the architecture bits needed to enable CONFIG_KEXEC_HANDOVER on
powerpc.

Set ARCH_SUPPORTS_KEXEC_HANDOVER for PPC64.

On the boot path, check for KHO information in the device tree before
unflatten_device_tree(). This allows a kernel booted via KHO kexec to
recover the FDT and scratch region left by the previous kernel.

Move early_init_dt_check_kho() out of the device tree implementation
and call it from setup_arch() before the device tree is unflattened.

Note:
Crashkernel reservation impacts KHO scratch reservation. Crashkernel
memory is reserved first using memblock, and this memory is included
when calculating the KHO scratch size. As a result, a large crashkernel
reservation can increase the KHO scratch size and may cause the KHO
scratch reservation to fail.

This issue also exists on other architectures and will be handled
separately.

Cc: Aditya Gupta <adityag@linux.ibm.com>
Cc: Alexander Graf <graf@amazon.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Pratyush Yadav <pratyush@kernel.org>
Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: Shivang Upadhyay <shivangu@linux.ibm.com>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: linux-kernel@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
---
 arch/powerpc/Kconfig               | 3 +++
 arch/powerpc/kernel/setup-common.c | 2 ++
 drivers/of/fdt.c                   | 2 +-
 include/linux/of_fdt.h             | 1 +
 4 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 2580e27e4328..3517d74949d0 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -716,6 +716,9 @@ config ARCH_SELECTS_CRASH_DUMP
 	depends on CRASH_DUMP
 	select RELOCATABLE if PPC64 || 44x || PPC_85xx
 
+config ARCH_SUPPORTS_KEXEC_HANDOVER
+	def_bool PPC64
+
 config ARCH_SUPPORTS_CRASH_HOTPLUG
 	def_bool y
 	depends on PPC64
diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
index 4afaba19b586..53c2f1897bfe 100644
--- a/arch/powerpc/kernel/setup-common.c
+++ b/arch/powerpc/kernel/setup-common.c
@@ -923,6 +923,8 @@ void __init setup_arch(char **cmdline_p)
 	/* Set a half-reasonable default so udelay does something sensible */
 	loops_per_jiffy = 500000000 / HZ;
 
+	early_init_dt_check_kho();
+
 	/* Unflatten the device-tree passed by prom_init or kexec */
 	unflatten_device_tree();
 
diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index a64afc3ded3d..69e6ad868fa3 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -926,7 +926,7 @@ void __init early_init_dt_check_for_usable_mem_range(void)
 /**
  * early_init_dt_check_kho - Decode info required for kexec handover from DT
  */
-static void __init early_init_dt_check_kho(void)
+void __init early_init_dt_check_kho(void)
 {
 	unsigned long node = chosen_node_offset;
 	u64 fdt_start, fdt_size, scratch_start, scratch_size;
diff --git a/include/linux/of_fdt.h b/include/linux/of_fdt.h
index 51dadbaa3d63..5e9d6af0c7dd 100644
--- a/include/linux/of_fdt.h
+++ b/include/linux/of_fdt.h
@@ -83,6 +83,7 @@ extern int early_init_dt_scan_root(void);
 extern bool early_init_dt_scan(void *dt_virt, phys_addr_t dt_phys);
 extern bool early_init_dt_verify(void *dt_virt, phys_addr_t dt_phys);
 extern void early_init_dt_scan_nodes(void);
+extern void early_init_dt_check_kho(void);
 
 extern const char *of_flat_dt_get_machine_name(void);
 extern const void *of_flat_dt_match_machine(const void *default_match,
-- 
2.55.0