[PATCH v11 4/5] arm64: kdump: add memory for devices by DT property linux,usable-memory-range

[Chen Zhou]

When reserving crashkernel in high memory, some low memory is reserved
for crash dump kernel devices and never mapped by the first kernel.
This memory range is advertised to crash dump kernel via DT property
under /chosen,
	linux,usable-memory-range = <BASE1 SIZE1 [BASE2 SIZE2]>

We reused the DT property linux,usable-memory-range and made the low
memory region as the second range "BASE2 SIZE2", which keeps compatibility
with existing user-space and older kdump kernels.

Crash dump kernel reads this property at boot time and call memblock_add()
to add the low memory region after memblock_cap_memory_range() has been
called.

Signed-off-by: Chen Zhou <chenzhou10@xxxxxxxxxx>
---
 arch/arm64/mm/init.c | 44 ++++++++++++++++++++++++++++++++++----------
 1 file changed, 34 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 53c8916fd32f..f385a8281d1b 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -69,6 +69,16 @@ EXPORT_SYMBOL(vmemmap);
 phys_addr_t arm64_dma_phys_limit __ro_after_init;
 phys_addr_t arm64_dma32_phys_limit __ro_after_init;
 
+/*
+ * The main usage of linux,usable-memory-range is for crash dump kernel.
+ * Originally, the number of usable-memory regions is one. Now there may
+ * be two regions, low region and high region.
+ * To make compatibility with existing user-space and older kdump, the low
+ * region is always the last range of linux,usable-memory-range if exist.
+ */
+#define MAX_USABLE_RANGES	2
+
+
 #ifdef CONFIG_KEXEC_CORE
 
 /*
@@ -286,9 +296,9 @@ early_param("mem", early_mem);
 static int __init early_init_dt_scan_usablemem(unsigned long node,
 		const char *uname, int depth, void *data)
 {
-	struct memblock_region *usablemem = data;
-	const __be32 *reg;
-	int len;
+	struct memblock_region *usable_rgns = data;
+	const __be32 *reg, *endp;
+	int len, nr = 0;
 
 	if (depth != 1 || strcmp(uname, "chosen") != 0)
 		return 0;
@@ -297,22 +307,36 @@ static int __init early_init_dt_scan_usablemem(unsigned long node,
 	if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
 		return 1;
 
-	usablemem->base = dt_mem_next_cell(dt_root_addr_cells, &reg);
-	usablemem->size = dt_mem_next_cell(dt_root_size_cells, &reg);
+	endp = reg + (len / sizeof(__be32));
+	while ((endp - reg) >= (dt_root_addr_cells + dt_root_size_cells)) {
+		usable_rgns[nr].base = dt_mem_next_cell(dt_root_addr_cells, &reg);
+		usable_rgns[nr].size = dt_mem_next_cell(dt_root_size_cells, &reg);
+
+		if (++nr >= MAX_USABLE_RANGES)
+			break;
+	}
 
 	return 1;
 }
 
 static void __init fdt_enforce_memory_region(void)
 {
-	struct memblock_region reg = {
-		.size = 0,
+	struct memblock_region usable_rgns[MAX_USABLE_RANGES] = {
+		{ .size = 0 },
+		{ .size = 0 }
 	};
 
-	of_scan_flat_dt(early_init_dt_scan_usablemem, &reg);
+	of_scan_flat_dt(early_init_dt_scan_usablemem, &usable_rgns);
 
-	if (reg.size)
-		memblock_cap_memory_range(reg.base, reg.size);
+	/*
+	 * The first range of usable-memory regions is for crash dump
+	 * kernel with only one region or for high region with two regions,
+	 * the second range is dedicated for low region if exist.
+	 */
+	if (usable_rgns[0].size)
+		memblock_cap_memory_range(usable_rgns[0].base, usable_rgns[0].size);
+	if (usable_rgns[1].size)
+		memblock_add(usable_rgns[1].base, usable_rgns[1].size);
 }
 
 void __init arm64_memblock_init(void)
-- 
2.20.1