[PATCH] [PATCH] ARM64: Setup DMA32 zone size by bootargs

[Phil Chang]

this patch allowing the DMA32 zone be configurable in ARM64.
For some devices, the main memory split into 2 part due to the memory
architecture, the efficient and less inefficient part.
One of the use case is fine-tune the dma32 size to contain all the
efficient part of memory block on this kind of architecture

Signed-off-by: Alix Wu <alix.wu@xxxxxxxxxxxx>
Signed-off-by: YJ Chiang <yj.chiang@xxxxxxxxxxxx>
Signed-off-by: Phil Chang <phil.chang@xxxxxxxxxxxx>
---
Hi

supplement the reason of this usage.

Thanks.

 .../admin-guide/kernel-parameters.txt         |  3 +++
 arch/arm64/include/asm/memory.h               |  2 ++
 arch/arm64/mm/init.c                          | 26 ++++++++++++++++++-
 3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index bdc1f33fd3d1..ef3bc3d4931a 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -980,6 +980,9 @@
 			The filter can be disabled or changed to another
 			driver later using sysfs.
 
+	dma32_size=nn[KMG]  [KNL,BOOT,ARM64]
+			Forces the DMA32 zone size of <nn> in MB.
+
 	driver_async_probe=  [KNL]
 			List of driver names to be probed asynchronously.
 			Format: <driver_name1>,<driver_name2>...
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index afa722504bfd..710de08ae8ae 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -175,6 +175,8 @@ extern u64			kimage_vaddr;
 /* the offset between the kernel virtual and physical mappings */
 extern u64			kimage_voffset;
 
+extern phys_addr_t		dma32_zone_size;
+
 static inline unsigned long kaslr_offset(void)
 {
 	return kimage_vaddr - KIMAGE_VADDR;
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 481d22c32a2e..fd1b85e131cc 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -60,6 +60,9 @@ EXPORT_SYMBOL(physvirt_offset);
 struct page *vmemmap __ro_after_init;
 EXPORT_SYMBOL(vmemmap);
 
+phys_addr_t dma32_zone_size __ro_after_init;
+EXPORT_SYMBOL(dma32_zone_size);
+
 /*
  * We create both ZONE_DMA and ZONE_DMA32. ZONE_DMA covers the first 1G of
  * memory as some devices, namely the Raspberry Pi 4, have peripherals with
@@ -189,7 +192,12 @@ static void __init reserve_elfcorehdr(void)
 static phys_addr_t __init max_zone_phys(unsigned int zone_bits)
 {
 	phys_addr_t offset = memblock_start_of_DRAM() & GENMASK_ULL(63, zone_bits);
-	return min(offset + (1ULL << zone_bits), memblock_end_of_DRAM());
+	phys_addr_t zone_size = (1ULL << zone_bits);
+
+	if (IS_ENABLED(CONFIG_ZONE_DMA32) && zone_bits == 32 && dma32_zone_size)
+		zone_size = min(zone_size, dma32_zone_size);
+
+	return min(offset + zone_size, memblock_end_of_DRAM());
 }
 
 static void __init zone_sizes_init(unsigned long min, unsigned long max)
@@ -242,6 +250,22 @@ static int __init early_mem(char *p)
 }
 early_param("mem", early_mem);
 
+static int __init setup_dma32_zone(char *p)
+{
+	unsigned long long size = memparse(p, NULL);
+
+	/* DMA32 zone size should never grater than 4G */
+	if (size > SZ_4G)
+		return -EINVAL;
+
+	pr_notice("Setup dma32 zone size to %llu Mb\n", size >> 20);
+	dma32_zone_size = size;
+
+	return 0;
+}
+
+early_param("dma32_size", setup_dma32_zone);
+
 static int __init early_init_dt_scan_usablemem(unsigned long node,
 		const char *uname, int depth, void *data)
 {
-- 
2.18.0