of: Improve compatibility with old Pi 5 firmware

arch/arm64/boot/dts/broadcom/bcm2712-ds.dtsi

@@ -60,6 +60,17 @@
 	};
 };
 
+/*
+ * With a #size-cells of 2, the 'size' property should be 2 cells long.
+ * Unfortunately the old firmware will only write the CMA value correctly
+ * if the property is 1 cell long. Fortunately the new firmware silently
+ * makes 'size' 2 cells long, so create what is actually an invalid DTS file
+ * on the understanding that it will be patched up as needed.
+ */
+&cma {
+	size = <0x4000000>; /* 64MB */
+};
+
 &soc {
 	system_timer: timer@7c003000 {
 		compatible = "brcm,bcm2835-system-timer";

drivers/of/fdt.c

@@ -1033,6 +1033,7 @@ int __init early_init_dt_scan_memory(void)
 
 	fdt_for_each_subnode(node, fdt, 0) {
 		const char *type = of_get_flat_dt_prop(node, "device_type", NULL);
+		int actual_size_cells = dt_root_size_cells;
 		const __be32 *reg, *endp;
 		int l;
 		bool hotpluggable;
@@ -1050,17 +1051,41 @@ int __init early_init_dt_scan_memory(void)
 		if (reg == NULL)
 			continue;
 
+		if (dt_root_size_cells == 2 &&
+		    l % ((dt_root_addr_cells + 1) * sizeof(__be32)) == 0) {
+			const int size_cells = 1;
+			const __be32 *r = reg;
+			bool ok = true;
+
+			/* Scan reg to see if the content makes sense with size-cells == 1 */
+			endp = reg + (l / sizeof(__be32));
+			while ((endp - r) >= (dt_root_addr_cells + size_cells)) {
+				const u64 megabyte = 1024 * 1024ull;
+				const u64 max_memory = 64 * 1024 * 1024 * 1024ull;
+				u64 base, size;
+
+				base = dt_mem_next_cell(dt_root_addr_cells, &r);
+				size = dt_mem_next_cell(size_cells, &r);
+				if (base % megabyte != 0 || base >= max_memory ||
+				    size % megabyte != 0 || size >= max_memory ||
+				    size == 0)
+					ok = false;
+			}
+			if (ok)
+				actual_size_cells = size_cells;
+		}
+
 		endp = reg + (l / sizeof(__be32));
 		hotpluggable = of_get_flat_dt_prop(node, "hotpluggable", NULL);
 
 		pr_debug("memory scan node %s, reg size %d,\n",
 			 fdt_get_name(fdt, node, NULL), l);
 
-		while ((endp - reg) >= (dt_root_addr_cells + dt_root_size_cells)) {
+		while ((endp - reg) >= (dt_root_addr_cells + actual_size_cells)) {
 			u64 base, size;
 
 			base = dt_mem_next_cell(dt_root_addr_cells, &reg);
-			size = dt_mem_next_cell(dt_root_size_cells, &reg);
+			size = dt_mem_next_cell(actual_size_cells, &reg);
 
 			if (size == 0)
 				continue;

drivers/of/of_reserved_mem.c

@@ -159,11 +159,25 @@ static int __init __reserved_mem_reserve_reg(unsigned long node,
 	int len;
 	const __be32 *prop;
 	bool nomap, default_cma;
+	int actual_size_cells = 0;
 
 	prop = of_get_flat_dt_prop(node, "reg", &len);
 	if (!prop)
 		return -ENOENT;
 
+	if (dt_root_addr_cells == 2 &&
+		dt_root_size_cells == 2 &&
+		len == (2 + 1) * sizeof(__be32)) {
+		pr_warn("invalid reg property size in '%s' - firmware out-of-date?\n",
+			uname);
+		actual_size_cells = 1;
+		t_len = (dt_root_addr_cells + actual_size_cells) * sizeof(__be32);
+	} else {
+		actual_size_cells = dt_root_size_cells;
+	}
+
+	t_len = (dt_root_addr_cells + actual_size_cells) * sizeof(__be32);
+
 	if (len && len % t_len != 0) {
 		pr_err("Reserved memory: invalid reg property in '%s', skipping node.\n",
 		       uname);
@@ -180,7 +194,7 @@ static int __init __reserved_mem_reserve_reg(unsigned long node,
 
 	while (len >= t_len) {
 		base = dt_mem_next_cell(dt_root_addr_cells, &prop);
-		size = dt_mem_next_cell(dt_root_size_cells, &prop);
+		size = dt_mem_next_cell(actual_size_cells, &prop);
 
 		if (size && early_init_dt_reserve_memory(base, size, nomap) == 0) {
 			/* Architecture specific contiguous memory fixup. */
@@ -267,8 +281,21 @@ void __init fdt_scan_reserved_mem_reg_nodes(void)
 		if (default_cma && cma_skip_dt_default_reserved_mem())
 			continue;
 
-		if (!of_flat_dt_get_addr_size(child, "reg", &b, &s))
-			continue;
+		if (!of_flat_dt_get_addr_size(child, "reg", &b, &s)) {
+			const __be32 *prop;
+			int size;
+
+			prop = of_get_flat_dt_prop(child, "reg", &size);
+			if (dt_root_addr_cells == 2 &&
+			    dt_root_size_cells == 2 &&
+			    size == 12) {
+				/* Handle this specific error case from old firmware */
+				b = of_read_number(prop, dt_root_addr_cells);
+				s = of_read_number(prop + 2, 1);
+			} else {
+				continue;
+			}
+		}
 
 		base = b;
 		size = s;
@@ -406,16 +433,24 @@ static int __init __reserved_mem_alloc_size(unsigned long node, const char *unam
 	const __be32 *prop;
 	bool nomap, default_cma;
 	int ret;
+	int actual_size_cells;
 
 	prop = of_get_flat_dt_prop(node, "size", &len);
 	if (!prop)
 		return -EINVAL;
+	if (dt_root_size_cells == 2 && len == sizeof(__be32)) {
+		pr_warn("invalid reg property size in '%s' - firmware out-of-date?\n",
+			uname);
+		actual_size_cells = 1;
+	} else {
+		actual_size_cells = dt_root_size_cells;
+	}
 
-	if (len != dt_root_size_cells * sizeof(__be32)) {
+	if (len != actual_size_cells * sizeof(__be32)) {
 		pr_err("invalid size property in '%s' node.\n", uname);
 		return -EINVAL;
 	}
-	size = dt_mem_next_cell(dt_root_size_cells, &prop);
+	size = dt_mem_next_cell(actual_size_cells, &prop);
 
 	prop = of_get_flat_dt_prop(node, "alignment", &len);
 	if (prop) {