Subject: [PATCH v4 2/2] powerpc/mm: Add memory_block_size as a kernel parameter

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Tue, 1 Aug 2023 10:14:47 +0530

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.

Reviewed-by: Reza Arbab <[email-masked]>
Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 .../admin-guide/kernel-parameters.txt         |  3 +++
 arch/powerpc/kernel/setup_64.c                | 23 +++++++++++++++++++
 arch/powerpc/mm/init_64.c                     | 17 ++++++++++----
 3 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a1457995fd41..4e49696e0976 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3201,6 +3201,9 @@
 			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..cbdb924462c7 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -892,6 +892,29 @@ unsigned long memory_block_size_bytes(void)
 
 	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;
+
+	memory_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)
diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
index d74d4a441616..fcda46c2b8df 100644
--- a/arch/powerpc/mm/init_64.c
+++ b/arch/powerpc/mm/init_64.c
@@ -566,13 +566,20 @@ static int __init probe_memory_block_size(unsigned long node, const char *uname,
 	return 0;
 }
 
-/*
- * start with 1G memory block size. Early init will
- * fix this with correct value.
- */
-unsigned long memory_block_size __ro_after_init = 1UL << 30;
+unsigned long memory_block_size __ro_after_init;
 static void __init early_init_memory_block_size(void)
 {
+	/*
+	 * if it is set via early param just return.
+	 */
+	if (memory_block_size)
+		return;
+
+	/*
+	 * start with 1G memory block size. update_memory_block_size()
+	 * will derive the right value based on device tree details.
+	 */
+	memory_block_size = SZ_1G;
 	/*
 	 * We need to do memory_block_size probe early so that
 	 * radix__early_init_mmu() can use this as limit for
-- 
2.41.0