linux设备树分析3-生成platform_device

上篇讲了从dtb文件转换成device_node树，本篇分析device_node生成platform_device平台设备的过程。

平台设备生成入口：在arch/arm64/kernel/setup.c文件中，入口函数为：

arm64_device_init->of_platform_populate

of_platform_populate在drivers/of/platform.c中定义：

int of_platform_populate(struct device_node *root,
			const struct of_device_id *matches,
			const struct of_dev_auxdata *lookup,
			struct device *parent)
{
	struct device_node *child;
	int rc = 0;

	/*获取根device_node节点*/
	root = root ? of_node_get(root) : of_find_node_by_path("/");
	if (!root)
		return -EINVAL;

	/*遍历根device_node的所有子节点，这里只是遍历了根节点的儿子节点，没有对孙子节点和其他节点进行处理*/
	for_each_child_of_node(root, child) {
		/*根据device_node生成platform_device*/
		rc = of_platform_bus_create(child, matches, lookup, parent, true);
		if (rc) {
			of_node_put(child);
			break;
		}
	}
	of_node_set_flag(root, OF_POPULATED_BUS);

	of_node_put(root);
	return rc;
}

static int of_platform_bus_create(struct device_node *bus,
				  const struct of_device_id *matches,
				  const struct of_dev_auxdata *lookup,
				  struct device *parent, bool strict)
{
	const struct of_dev_auxdata *auxdata;
	struct device_node *child;
	struct platform_device *dev;
	const char *bus_id = NULL;
	void *platform_data = NULL;
	int rc = 0;

	/* Make sure it has a compatible property */
	/*device_node节点必须具有“compatible”属性才会继续解析*/
	if (strict && (!of_get_property(bus, "compatible", NULL))) {
		pr_debug("%s() - skipping %s, no compatible prop\n",
			 __func__, bus->full_name);
		return 0;
	}

	/*设备拓展数据暂时不讨论*/
	auxdata = of_dev_lookup(lookup, bus);
	if (auxdata) {
		bus_id = auxdata->name;
		platform_data = auxdata->platform_data;
	}
    
    /*对于compatible 属性为"arm,primecell"的节点需要特殊处理*/
	if (of_device_is_compatible(bus, "arm,primecell")) {
		/*
		 * Don't return an error here to keep compatibility with older
		 * device tree files.
		 */
		of_amba_device_create(bus, bus_id, platform_data, parent);
		return 0;
	}
	/*将device_node 属性解析生成platform_device设备属性*/
	dev = of_platform_device_create_pdata(bus, bus_id, platform_data, parent);
	if (!dev || !of_match_node(matches, bus))
		return 0;

	/*之前提到第一次遍历时只处理的根节点的儿子节点，这里通过遍历当前节点的子节点，来处理根节点的孙子节点，实际上通过这种方式最终递归遍历所有节点*/
	for_each_child_of_node(bus, child) {
		pr_debug("   create child: %s\n", child->full_name);
		rc = of_platform_bus_create(child, matches, lookup, &dev->dev, strict);
		if (rc) {
			of_node_put(child);
			break;
		}
	}
	of_node_set_flag(bus, OF_POPULATED_BUS);
	return rc;
}


static struct platform_device *of_platform_device_create_pdata(
					struct device_node *np,
					const char *bus_id,
					void *platform_data,
					struct device *parent)
{
	struct platform_device *dev;

	/*如果device_node节点没有被创建过且节点状态有效则创建platform_device，节点是否有效是通过节点的status属性来判断的，如果status属性值为”ok”或者” okay”则有效*/
	if (!of_device_is_available(np) ||
	    of_node_test_and_set_flag(np, OF_POPULATED))
		return NULL;
	/*申请platform_device空间，初始化platform_device的io和中断资源*/
	dev = of_device_alloc(np, bus_id, parent);
	if (!dev)
		goto err_clear_flag;

	dev->dev.bus = &platform_bus_type;
	dev->dev.platform_data = platform_data;
	/*设置platform_device的中dma*/
	of_dma_configure(&dev->dev, dev->dev.of_node);
	/*设置platform_device的msi中断*/
	of_msi_configure(&dev->dev, dev->dev.of_node);

	/*将platform_device挂到总线，到此平台设备已经创建完了，这是加载对应驱动后就可以对设备进行读写操作了*/
	if (of_device_add(dev) != 0) {
		of_dma_deconfigure(&dev->dev);
		platform_device_put(dev);
		goto err_clear_flag;
	}

	return dev;

err_clear_flag:
	of_node_clear_flag(np, OF_POPULATED);
	return NULL;
}

struct platform_device *of_device_alloc(struct device_node *np,
				  const char *bus_id,
				  struct device *parent)
{
	struct platform_device *dev;
	int rc, i, num_reg = 0, num_irq;
	struct resource *res, temp_res;
	/*申请platform_device内存空间*/
	dev = platform_device_alloc("", -1);
	if (!dev)
		return NULL;

	/* count the io and irq resources */
	/*通过节点“reg”属性结算节点的io和mem资源数*/
	while (of_address_to_resource(np, num_reg, &temp_res) == 0)
		num_reg++;

	/*通过节点“interrupts”和“#interrupt-cells”属性计算节点的中断数*/
	num_irq = of_irq_count(np);

	/* Populate the resource table */
	/*根据资源和中断数申请内存，并初始化节点资源*/
	if (num_irq || num_reg) {
		/*申请platform_device存储资源的空间*/
		res = kzalloc(sizeof(*res) * (num_irq + num_reg), GFP_KERNEL);
		if (!res) {
			platform_device_put(dev);
			return NULL;
		}

		dev->num_resources = num_reg + num_irq;
		dev->resource = res;
		/*解析节点reg属性，生成platform_device的io或者mem资源，将其保存在resource 中*/
		for (i = 0; i < num_reg; i++, res++) {
			rc = of_address_to_resource(np, i, res);
			WARN_ON(rc);
		}
		/*解析节点中断属性，生成platform_device的irq资源，将其保存在resource中*/
		if (of_irq_to_resource_table(np, res, num_irq) != num_irq)
			pr_debug("not all legacy IRQ resources mapped for %s\n",
				 np->name);
	}

	/*platform_device的of_node指针指向当前device_node*/
dev->dev.of_node = of_node_get(np);
/*初始化platform_device的父设备 */
	dev->dev.parent = parent ? : &platform_bus;

 	/*设置platform_device设备名称*/
	if (bus_id)
		dev_set_name(&dev->dev, "%s", bus_id);
	else
		of_device_make_bus_id(&dev->dev);

	return dev;
}