1. machine_desc的匹配
《这篇》有介绍DT_MACHINE_START的一些初始化操作，匹配上就会在后续的初始化中调用DT_MACHINE_START的成员来初始化系统的设备树，时钟，中断等
start_kernelsetup_arch(&command_line);mdesc = setup_machine_fdt(atags_vaddr) //返回成功匹配的machine_desc....unflatten_device_tree(); //将设备树解析成device_node1.1 setup_machine_fdt
early_init_dt_verify校验设备树，和初始化设备树指针；然后of_flat_dt_match_machine匹配MACHINE_START定义machine_desc和设备树
const struct machine_desc * __init setup_machine_fdt(void *dt_virt)
{const struct machine_desc *mdesc, *mdesc_best = NULL;#if defined(CONFIG_ARCH_MULTIPLATFORM) || defined(CONFIG_ARM_SINGLE_ARMV7M)DT_MACHINE_START(GENERIC_DT, "Generic DT based system").l2c_aux_val = 0x0,.l2c_aux_mask = ~0x0,MACHINE_ENDmdesc_best = &__mach_desc_GENERIC_DT;
#endifif (!dt_virt || !early_init_dt_verify(dt_virt))return NULL;mdesc = of_flat_dt_match_machine(mdesc_best, arch_get_next_mach);if (!mdesc) {const char *prop;int size;unsigned long dt_root;early_print("\nError: unrecognized/unsupported ""device tree compatible list:\n[ ");dt_root = of_get_flat_dt_root();prop = of_get_flat_dt_prop(dt_root, "compatible", &size);while (size > 0) {early_print("'%s' ", prop);size -= strlen(prop) + 1;prop += strlen(prop) + 1;}early_print("]\n\n");dump_machine_table(); /* does not return */}/* We really don't want to do this, but sometimes firmware provides buggy data */if (mdesc->dt_fixup)mdesc->dt_fixup();early_init_dt_scan_nodes();/* Change machine number to match the mdesc we're using */__machine_arch_type = mdesc->nr;return mdesc;
}1.2 early_init_dt_verify
将设备树指针给到initial_boot_params，供后续直接对设备树操作的api使用
bool __init early_init_dt_verify(void *params)
{if (!params)return false;/* check device tree validity */if (fdt_check_header(params))return false;/* Setup flat device-tree pointer */initial_boot_params = params;of_fdt_crc32 = crc32_be(~0, initial_boot_params,fdt_totalsize(initial_boot_params));return true;
}1.3 of_flat_dt_match_machine
of_flat_dt_match去匹配设备树跟machine_desc的dt_compat成员
const void * __init of_flat_dt_match_machine(const void *default_match,const void * (*get_next_compat)(const char * const**))
{const void *data = NULL;const void *best_data = default_match;const char *const *compat;unsigned long dt_root;unsigned int best_score = ~1, score = 0;dt_root = of_get_flat_dt_root();while ((data = get_next_compat(&compat))) {score = of_flat_dt_match(dt_root, compat);if (score > 0 && score < best_score) {best_data = data;best_score = score;}}if (!best_data) {const char *prop;int size;pr_err("\n unrecognized device tree list:\n[ ");prop = of_get_flat_dt_prop(dt_root, "compatible", &size);if (prop) {while (size > 0) {printk("'%s' ", prop);size -= strlen(prop) + 1;prop += strlen(prop) + 1;}}printk("]\n\n");return NULL;}pr_info("Machine model: %s\n", of_flat_dt_get_machine_name());return best_data;
}1.4 of_flat_dt_match
of_fdt_is_compatible通过设备树指针initial_boot_params找到兼容属性
static int __init of_flat_dt_match(unsigned long node, const char *const *compat)
{unsigned int tmp, score = 0;if (!compat)return 0;while (*compat) {tmp = of_fdt_is_compatible(initial_boot_params, node, *compat);if (tmp && (score == 0 || (tmp < score)))score = tmp;compat++;}return score;
}1.5 of_fdt_is_compatible
通过fdt_getprop直接获取compatible 属性，并比较字符串来看匹配上没
static int of_fdt_is_compatible(const void *blob,unsigned long node, const char *compat)
{const char *cp;int cplen;unsigned long l, score = 0;cp = fdt_getprop(blob, node, "compatible", &cplen);if (cp == NULL)return 0;while (cplen > 0) {score++;if (of_compat_cmp(cp, compat, strlen(compat)) == 0)return score;l = strlen(cp) + 1;cp += l;cplen -= l;}return 0;
}2. device_node的生成
通过上面赋值的initial_boot_params，去将设备树解析成device_node结构的树
void __init unflatten_device_tree(void)
{__unflatten_device_tree(initial_boot_params, NULL, &of_root,early_init_dt_alloc_memory_arch, false);/* Get pointer to "/chosen" and "/aliases" nodes for use everywhere */of_alias_scan(early_init_dt_alloc_memory_arch);unittest_unflatten_overlay_base();
}2.1 unflatten_dt_nodes
通过populate_node填充device_node
static int unflatten_dt_nodes(const void *blob,void *mem,struct device_node *dad,struct device_node **nodepp)
{struct device_node *root;int offset = 0, depth = 0, initial_depth = 0;
#define FDT_MAX_DEPTH 64struct device_node *nps[FDT_MAX_DEPTH];void *base = mem;bool dryrun = !base;if (nodepp)*nodepp = NULL;/** We're unflattening device sub-tree if @dad is valid. There are* possibly multiple nodes in the first level of depth. We need* set @depth to 1 to make fdt_next_node() happy as it bails* immediately when negative @depth is found. Otherwise, the device* nodes except the first one won't be unflattened successfully.*/if (dad)depth = initial_depth = 1;root = dad;nps[depth] = dad;for (offset = 0;offset >= 0 && depth >= initial_depth;offset = fdt_next_node(blob, offset, &depth)) {if (WARN_ON_ONCE(depth >= FDT_MAX_DEPTH))continue;if (!IS_ENABLED(CONFIG_OF_KOBJ) &&!of_fdt_device_is_available(blob, offset))continue;if (!populate_node(blob, offset, &mem, nps[depth],&nps[depth+1], dryrun))return mem - base;if (!dryrun && nodepp && !*nodepp)*nodepp = nps[depth+1];if (!dryrun && !root)root = nps[depth+1];}if (offset < 0 && offset != -FDT_ERR_NOTFOUND) {pr_err("Error %d processing FDT\n", offset);return -EINVAL;}/** Reverse the child list. Some drivers assumes node order matches .dts* node order*/if (!dryrun)reverse_nodes(root);return mem - base;
}2.2 populate_node
unflatten_dt_alloc分配节点，并通过populate_properties填充各属性
static bool populate_node(const void *blob,int offset,void **mem,struct device_node *dad,struct device_node **pnp,bool dryrun)
{struct device_node *np;const char *pathp;unsigned int l, allocl;pathp = fdt_get_name(blob, offset, &l);if (!pathp) {*pnp = NULL;return false;}allocl = ++l;np = unflatten_dt_alloc(mem, sizeof(struct device_node) + allocl,__alignof__(struct device_node));if (!dryrun) {char *fn;of_node_init(np);np->full_name = fn = ((char *)np) + sizeof(*np);memcpy(fn, pathp, l);if (dad != NULL) {np->parent = dad;np->sibling = dad->child;dad->child = np;}}populate_properties(blob, offset, mem, np, pathp, dryrun);if (!dryrun) {np->name = of_get_property(np, "name", NULL);if (!np->name)np->name = "<NULL>";}*pnp = np;return true;
}3. paltform_device的生成
3.1 init_machine
MACHINE_START中含有一个.dt_compat成员，根据设备树的compatible属性来--锚定具体的machine_desc，；后续也会用init_machine来通过of_platform_populate，构造platfoem_device
static void __init xxx_dt_init_machine(void)
{/* mmp_entry_vector_init(); */of_platform_populate(NULL, of_default_bus_match_table,xxx_auxdata_lookup, NULL);}static const char *XXX_dt_board_compat[] __initdata = {"id-xxx,id-yyy",NULL,
};DT_MACHINE_START(XXX_DT, "XXX (Device Tree Support)").map_io = mmp_map_io,.init_irq = irqchip_init,.init_time = xxx_init_time,.reserve = xxx_reserve,.init_machine = xxx_dt_init_machine,.dt_compat = xxx_dt_board_compat,.restart = xxx_arch_restart,
MACHINE_END3.2 什么时候生成
系统初始化跑完了，在最后会执行kernel_init这个1号进程；去初始化initcall，和其他的一些初始化操作，最后成为用户层的init进程
start_kernelarch_call_rest_initkernel_initkernel_init_freeabledo_basic_setup()do_initcalls()static int __init customize_machine(void)
{/** customizes platform devices, or adds new ones* On DT based machines, we fall back to populating the* machine from the device tree, if no callback is provided,* otherwise we would always need an init_machine callback.*/if (machine_desc->init_machine)machine_desc->init_machine();return 0;
}
arch_initcall(customize_machine);3.3 什么节点会被生成
1.一般情况下，只对设备树中根的一级子节点进行转换，也就是多级子节点(子节点的子节点)并不处理。
2.但是存在一种特殊情况，就是当某个根子节点的compatible属性为"simple-bus"、"simple-mfd"、"isa"、"arm,amba-bus"时，当前节点中的一级子节点将会被转换成platform_device节点。
3.节点中必须有compatible属性。
const struct of_device_id of_default_bus_match_table[] = {{ .compatible = "simple-bus", },{ .compatible = "simple-mfd", },{ .compatible = "isa", },
#ifdef CONFIG_ARM_AMBA{ .compatible = "arm,amba-bus", },
#endif /* CONFIG_ARM_AMBA */{} /* Empty terminated list */
};3.4 生成platfoem_device
终于到了产生platfoem_device地方:
(1)不再直接使用设备树，而是使用前面生成的device_node
(2)matches作为匹配表(of_default_bus_match_table); lookup作为platform_data(xxx_auxdata_lookup)
(3)生成细节见我们的《这篇》
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;root = root ? of_node_get(root) : of_find_node_by_path("/");if (!root)return -EINVAL;pr_debug("%s()\n", __func__);pr_debug(" starting at: %pOF\n", root);for_each_child_of_node(root, child) {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;
}
