[PATCH 5/8] arm64: use ZONE_DMA on DMA addressing limited devices

[Nicolas Saenz Julienne <nsaenzjulienne@suse.de>]

So far all arm64 devices have supported 32 bit DMA masks for their
peripherals. This is not true anymore for the Raspberry Pi 4. Most of
it's peripherals can only address the first GB or memory of a total of
up to 4 GB.

This goes against ZONE_DMA32's original intent, and breaks other
subsystems as it's expected for ZONE_DMA32 to be addressable with a 32
bit mask. So it was decided to use ZONE_DMA for this specific case.

Devices with with 32 bit DMA addressing support will still bypass
ZONE_DMA but those who don't will create both zones. ZONE_DMA will
contain the memory addressable by all the SoC's devices and ZONE_DMA32
the rest of the 32 bit addressable memory.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
---

 arch/arm64/Kconfig   |  4 ++++
 arch/arm64/mm/init.c | 38 ++++++++++++++++++++++++++++++++------
 2 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 3adcec05b1f6..a9fd71d3bc8e 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -266,6 +266,10 @@ config GENERIC_CSUM
 config GENERIC_CALIBRATE_DELAY
 	def_bool y
 
+config ZONE_DMA
+	bool "Support DMA zone" if EXPERT
+	default y
+
 config ZONE_DMA32
 	bool "Support DMA32 zone" if EXPERT
 	default y
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 1c4ffabbe1cb..f5279ef85756 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -50,6 +50,13 @@
 s64 memstart_addr __ro_after_init = -1;
 EXPORT_SYMBOL(memstart_addr);
 
+/*
+ * We might create both a ZONE_DMA and ZONE_DMA32. ZONE_DMA is needed if there
+ * are periferals unable to address the first naturally aligned 4GB of ram.
+ * ZONE_DMA32 will be expanded to cover the rest of that memory. If such
+ * limitations doesn't exist only ZONE_DMA32 is created.
+ */
+phys_addr_t arm64_dma_phys_limit __ro_after_init;
 phys_addr_t arm64_dma32_phys_limit __ro_after_init;
 
 #ifdef CONFIG_KEXEC_CORE
@@ -193,6 +200,9 @@ 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
+	max_zone_pfns[ZONE_DMA] = PFN_DOWN(arm64_dma_phys_limit);
+#endif
 #ifdef CONFIG_ZONE_DMA32
 	max_zone_pfns[ZONE_DMA32] = PFN_DOWN(arm64_dma32_phys_limit);
 #endif
@@ -207,14 +217,19 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
 {
 	struct memblock_region *reg;
 	unsigned long zone_size[MAX_NR_ZONES], zhole_size[MAX_NR_ZONES];
+	unsigned long max_dma = PFN_DOWN(arm64_dma_phys_limit);
 	unsigned long max_dma32 = min;
 
 	memset(zone_size, 0, sizeof(zone_size));
 
+#ifdef CONFIG_ZONE_DMA
+	if (max_dma)
+		zone_size[ZONE_DMA] = max_dma - min;
+#endif
 	/* 4GB maximum for 32-bit only capable devices */
 #ifdef CONFIG_ZONE_DMA32
 	max_dma32 = PFN_DOWN(arm64_dma32_phys_limit);
-	zone_size[ZONE_DMA32] = max_dma32 - min;
+	zone_size[ZONE_DMA32] = max_dma32 - max_dma - min;
 #endif
 	zone_size[ZONE_NORMAL] = max - max_dma32;
 
@@ -226,11 +241,17 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
 
 		if (start >= max)
 			continue;
-
+#ifdef CONFIG_ZONE_DMA
+		if (start < max_dma) {
+			unsigned long dma_end = min_not_zero(end, max_dma);
+			zhole_size[ZONE_DMA] -= dma_end - start;
+		}
+#endif
 #ifdef CONFIG_ZONE_DMA32
 		if (start < max_dma32) {
-			unsigned long dma_end = min(end, max_dma32);
-			zhole_size[ZONE_DMA32] -= dma_end - start;
+			unsigned long dma32_end = min(end, max_dma32);
+			unsigned long dma32_start = max(start, max_dma);
+			zhole_size[ZONE_DMA32] -= dma32_end - dma32_start;
 		}
 #endif
 		if (end > max_dma32) {
@@ -418,6 +439,11 @@ void __init arm64_memblock_init(void)
 
 	early_init_fdt_scan_reserved_mem();
 
+	if (IS_ENABLED(CONFIG_ZONE_DMA))
+		arm64_dma_phys_limit = max_zone_dma_phys();
+	else
+		arm64_dma_phys_limit = 0;
+
 	/* 4GB maximum for 32-bit only capable devices */
 	if (IS_ENABLED(CONFIG_ZONE_DMA32))
 		arm64_dma32_phys_limit = max_zone_dma32_phys();
@@ -430,7 +456,7 @@ void __init arm64_memblock_init(void)
 
 	high_memory = __va(memblock_end_of_DRAM() - 1) + 1;
 
-	dma_contiguous_reserve(arm64_dma32_phys_limit);
+	dma_contiguous_reserve(arm64_dma_phys_limit ? : arm64_dma32_phys_limit);
 }
 
 void __init bootmem_init(void)
@@ -533,7 +559,7 @@ static void __init free_unused_memmap(void)
  */
 void __init mem_init(void)
 {
-	if (swiotlb_force == SWIOTLB_FORCE ||
+	if (swiotlb_force == SWIOTLB_FORCE || arm64_dma_phys_limit ||
 	    max_pfn > (arm64_dma32_phys_limit >> PAGE_SHIFT))
 		swiotlb_init(1);
 	else
-- 
2.22.0

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