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_kernel
setup_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_END
mdesc_best = &__mach_desc_GENERIC_DT;
#endif
if (!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 64
struct 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_kernel
arch_call_rest_init
kernel_init
kernel_init_freeable
do_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;
}
