powerpc: export MIN RMA size

Commit 683eab9 ("powerpc/fadump: setup additional parameters for
dump capture kernel") introduced the additional parameter feature in
fadump for HASH MMU with the understanding that GRUB does not use the
memory area between 640MB and 768MB for its operation.

However, the third patch ("powerpc: increase MIN RMA size for CAS
negotiation") in this series is changing the MIN RMA size to 768MB,
allowing GRUB to use memory up to 768MB. This makes the fadump
reservation for the additional parameter feature for HASH MMU
unreliable.

To address this, export the MIN_RMA so that the next patch
("powerpc/fadump: fix additional param memory reservation for HASH MMU")
can identify the correct memory range for the additional parameter
feature in fadump for HASH MMU.

Reviewed-by: Mahesh Salgaonkar <[email protected]>
Signed-off-by: Sourabh Jain <[email protected]>
Signed-off-by: Madhavan Srinivasan <[email protected]>
Link: https://patch.msgid.link/[email protected]

Author: sourabhjains

arch/powerpc/include/asm/prom.h

@@ -17,6 +17,8 @@
 struct device_node;
 struct property;
 
+#define MIN_RMA			512		/* Minimum RMA (in MB) for CAS negotiation */
+
 #define OF_DT_BEGIN_NODE	0x1		/* Start of node, full name */
 #define OF_DT_END_NODE		0x2		/* End node */
 #define OF_DT_PROP		0x3		/* Property: name off, size,

arch/powerpc/kernel/prom_init.c

@@ -1061,7 +1061,7 @@ static const struct ibm_arch_vec ibm_architecture_vec_template __initconst = {
 		.virt_base = cpu_to_be32(0xffffffff),
 		.virt_size = cpu_to_be32(0xffffffff),
 		.load_base = cpu_to_be32(0xffffffff),
-		.min_rma = cpu_to_be32(512),		/* 512MB min RMA */
+		.min_rma = cpu_to_be32(MIN_RMA),
 		.min_load = cpu_to_be32(0xffffffff),	/* full client load */
 		.min_rma_percent = 0,	/* min RMA percentage of total RAM */
 		.max_pft_size = 48,	/* max log_2(hash table size) */