[PATCH] ARM64: Setup DMA32 zone size by bootargs

[Phil Chang]

this patch allowing the arm64 DMA zone be configurable.

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

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,
but in general, the DMA32 zone size is hardcode to 4G.

 .../admin-guide/kernel-parameters.txt         |  3 ++
 arch/arm64/include/asm/memory.h               |  2 ++
 arch/arm64/mm/init.c                          | 33 +++++++++++++++++--
 3 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index fb95fad81c79..441ad3cb8ee8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -956,6 +956,9 @@
 			The filter can be disabled or changed to another
 			driver later using sysfs.
 
+	dma32_zone=nn	[KMG] [KNL,BOOT]
+			Forces the DMA32 zone size of <nn> in mb, arm64 only.
+
 	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 a1871bb32bb1..377f2252618a 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -174,6 +174,8 @@ extern u64			kimage_vaddr;
 /* the offset between the kernel virtual and physical mappings */
 extern u64			kimage_voffset;
 
+extern phys_addr_t		arm_dma_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 1e93cfc7c47a..642ab323392c 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 arm_dma_zone_size __ro_after_init;
+EXPORT_SYMBOL(arm_dma_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
@@ -242,6 +245,25 @@ static int __init early_mem(char *p)
 }
 early_param("mem", early_mem);
 
+/*
+ * Setup the dma32 zone size
+ */
+static int __init setup_dma32_zone(char *p)
+{
+	if (!p)
+		return -EINVAL;
+
+	if (kstrtoull(p, 0, &arm_dma_zone_size))
+		return -EINVAL;
+
+	arm_dma_zone_size *= SZ_1M;
+	pr_notice("Setup dma32 zone size to %llu Mb\n", arm_dma_zone_size);
+
+	return 0;
+}
+
+early_param("dma32_zone", setup_dma32_zone);
+
 static int __init early_init_dt_scan_usablemem(unsigned long node,
 		const char *uname, int depth, void *data)
 {
@@ -392,10 +414,15 @@ void __init arm64_memblock_init(void)
 		arm64_dma_phys_limit = max_zone_phys(ARM64_ZONE_DMA_BITS);
 	}
 
-	if (IS_ENABLED(CONFIG_ZONE_DMA32))
-		arm64_dma32_phys_limit = max_zone_phys(32);
-	else
+	if (IS_ENABLED(CONFIG_ZONE_DMA32)) {
+		if (arm_dma_zone_size)
+			arm64_dma32_phys_limit = arm_dma_zone_size +
+						memblock_start_of_DRAM();
+		else
+			arm64_dma32_phys_limit = max_zone_phys(32);
+	} else {
 		arm64_dma32_phys_limit = PHYS_MASK + 1;
+	}
 
 	reserve_crashkernel();
 
-- 
2.18.0