linux kernel記憶體管理學習篇

目錄

• • • 1、DDR的注冊
    • • (1)、在dts中定義了DDR(memory)的範圍
      • (2)、将DDR位址範圍注冊到linux kernel
    • 2、reserved-memory的注冊
    • • (1)、在dts中定義了reserved-memory的範圍
      • (2)、将reserved memory資訊告知給linux kernel

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1、DDR的注冊

(1)、在dts中定義了DDR(memory)的範圍

[email protected] {
        device_type = "memory";
        reg = <0x0 0x80000000 0x2 0x0>;
};
           

(2)、将DDR位址範圍注冊到linux kernel

early_init_dt_scan_memory()

early_init_dt_scan_memory() —> early_init_dt_add_memory_arch(base, size) —> memblock_add(base, size)—>memblock_add_region(base, size, MAX_NUMNODES, 0)

(driver/of/fdt.c)
/**
 * early_init_dt_scan_memory - Look for an parse memory nodes
 */
int __init early_init_dt_scan_memory(unsigned long node, const char *uname,
				     int depth, void *data)
{
	const char *type = of_get_flat_dt_prop(node, "device_type", NULL);
	const __be32 *reg, *endp;
	int l;

	/* We are scanning "memory" nodes only */
	if (type == NULL) {
		/*
		 * The longtrail doesn't have a device_type on the
		 * /memory node, so look for the node called /[email protected].
		 */
		if (!IS_ENABLED(CONFIG_PPC32) || depth != 1 || strcmp(uname, "[email protected]") != 0)
			return 0;
	} else if (strcmp(type, "memory") != 0)
		return 0;

	reg = of_get_flat_dt_prop(node, "linux,usable-memory", &l);
	if (reg == NULL)
		reg = of_get_flat_dt_prop(node, "reg", &l);
	if (reg == NULL)
		return 0;

	endp = reg + (l / sizeof(__be32));

	pr_debug("memory scan node %s, reg size %d,\n", uname, l);

	while ((endp - reg) >= (dt_root_addr_cells + dt_root_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);

		if (size == 0)
			continue;
		pr_debug(" - %llx ,  %llx\n", (unsigned long long)base,
		    (unsigned long long)size);

		early_init_dt_add_memory_arch(base, size);
	}

	return 0;
}
           

MAX_NUMNODES表示有幾塊DDR區域(注意是幾塊DDR區域，并不是幾塊DDR)，大小為1(1<<0)或和CONFIG_NODES_SHIFT值相關

#define MAX_NUMNODES    (1 << NODES_SHIFT)

#ifdef CONFIG_NODES_SHIFT
#define NODES_SHIFT     CONFIG_NODES_SHIFT
#else
#define NODES_SHIFT     0
#endif
           

2、reserved-memory的注冊

(1)、在dts中定義了reserved-memory的範圍

reserved-memory {
	#address-cells = <1>;
	#size-cells = <1>;
	ranges;

		/* global autoconfigured region for contiguous allocations */
		linux,cma {
			compatible = "shared-dma-pool";
			reusable;
			size = <0x4000000>;
			alignment = <0x2000>;
			linux,cma-default;
		};

		display_reserved: framebuffer@78000000 {
			reg = <0x78000000 0x800000>;
		};

		multimedia_reserved: multimedia@77000000 {
			compatible = "acme,multimedia-memory";
			reg = <0x77000000 0x4000000>;
		};
	};

	/* ... */

	fb0: video@12300000 {
		memory-region = <&display_reserved>;
		/* ... */
	};

	scaler: scaler@12500000 {
		memory-region = <&multimedia_reserved>;
		/* ... */
	};

	codec: codec@12600000 {
		memory-region = <&multimedia_reserved>;
		/* ... */
	};
           

(2)、将reserved memory資訊告知給linux kernel

__fdt_scan_reserved_mem()

__fdt_scan_reserved_mem() —> __reserved_mem_reserve_reg() —> early_init_dt_reserve_memory_arch(base, size, nomap)—>memblock_reserve(base, size) —> memblock_reserve_region(base, size, MAX_NUMNODES, 0)

(driver/of/fdt.c)
/**
 * fdt_scan_reserved_mem() - scan a single FDT node for reserved memory
 */
static int __init __fdt_scan_reserved_mem(unsigned long node, const char *uname,
					  int depth, void *data)
{
	static int found;
	const char *status;
	int err;

	if (!found && depth == 1 && strcmp(uname, "reserved-memory") == 0) {
		if (__reserved_mem_check_root(node) != 0) {
			pr_err("Reserved memory: unsupported node format, ignoring\n");
			/* break scan */
			return 1;
		}
		found = 1;
		/* scan next node */
		return 0;
	} else if (!found) {
		/* scan next node */
		return 0;
	} else if (found && depth < 2) {
		/* scanning of /reserved-memory has been finished */
		return 1;
	}

	status = of_get_flat_dt_prop(node, "status", NULL);
	if (status && strcmp(status, "okay") != 0 && strcmp(status, "ok") != 0)
		return 0;

	err = __reserved_mem_reserve_reg(node, uname);
	if (err == -ENOENT && of_get_flat_dt_prop(node, "size", NULL))
		fdt_reserved_mem_save_node(node, uname, 0, 0);

	/* scan next node */
	return 0;
}