[PATCH v2 4/5] arm64: mm: Dynamically resize zone_dma_bits based on system's constraints

[Nicolas Saenz Julienne]

With the help of of_dma_safe_phys_limit() we can get the topmost
physical address accessible for DMA to the whole system and use that
information to properly setup zone_dma_bits.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
---
 arch/arm64/include/asm/processor.h | 1 +
 arch/arm64/mm/init.c               | 5 ++---
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index fce8cbecd6bc..c09d3f1a9a6b 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -97,6 +97,7 @@
 
 extern phys_addr_t arm64_dma_phys_limit;
 #define ARCH_LOW_ADDRESS_LIMIT	(arm64_dma_phys_limit - 1)
+#define ZONE_DMA_BITS_DEFAULT	32
 
 struct debug_info {
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 0eca5865dcb1..5934df93bf4d 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -42,8 +42,6 @@
 #include <asm/tlb.h>
 #include <asm/alternative.h>
 
-#define ARM64_ZONE_DMA_BITS	30
-
 /*
  * We need to be able to catch inadvertent references to memstart_addr
  * that occur (potentially in generic code) before arm64_memblock_init()
@@ -196,7 +194,8 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
 	unsigned long max_zone_pfns[MAX_NR_ZONES]  = {0};
 
 #ifdef CONFIG_ZONE_DMA
-	zone_dma_bits = ARM64_ZONE_DMA_BITS;
+	zone_dma_bits = min(zone_dma_bits,
+			    (unsigned int)ilog2(of_dma_safe_phys_limit()));
 
 	if (IS_ENABLED(CONFIG_ACPI)) {
 		extern unsigned int acpi_iort_get_zone_dma_size(void);
-- 
2.28.0