[PATCH 2/2] powerpc/mm: Add memory_block_size as a kernel parameter

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

Certain devices can possess non-standard memory capacities, not constrained
to multiples of 1GB. Provide a kernel parameter so that we can map the
device memory completely on memory hotplug.

Restrict memory_block_size value to a power of 2 value similar to LMB size.
The memory block size should also be more than the section size.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 .../admin-guide/kernel-parameters.txt         |  3 +++
 arch/powerpc/kernel/setup_64.c                | 27 +++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9e5bab29685f..833b8c5b4b4c 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3190,6 +3190,9 @@
 			Note that even when enabled, there are a few cases where
 			the feature is not effective.
 
+	memory_block_size=size [PPC]
+			 Use this parameter to configure the memory block size value.
+
 	memtest=	[KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest
 			Format: <integer>
 			default : 0 <disable>
diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 246201d0d879..54ce748a340d 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -885,13 +885,40 @@ void __init setup_per_cpu_areas(void)
 #endif
 
 #ifdef CONFIG_MEMORY_HOTPLUG
+static unsigned long set_mem_block_size;
 unsigned long memory_block_size_bytes(void)
 {
+	if (set_mem_block_size)
+		return set_mem_block_size;
+
 	if (ppc_md.memory_block_size)
 		return ppc_md.memory_block_size();
 
 	return MIN_MEMORY_BLOCK_SIZE;
 }
+
+/*
+ * Restrict to a power of 2 value for memblock which is larger than
+ * section size
+ */
+static int __init parse_mem_block_size(char *ptr)
+{
+	unsigned int order;
+	unsigned long size = memparse(ptr, NULL);
+
+	order = fls64(size);
+	if (!order)
+		return 0;
+
+	order--;
+	if (order < SECTION_SIZE_BITS)
+		return 0;
+
+	set_mem_block_size = 1UL << order;
+
+	return 0;
+}
+early_param("memory_block_size", parse_mem_block_size);
 #endif
 
 #if defined(CONFIG_PPC_INDIRECT_PIO) || defined(CONFIG_PPC_INDIRECT_MMIO)
-- 
2.40.1