1，设备树的引入
2，uboot本身对设备树的支持
3，对uboot中设备树节点解析代码的分析
（1）上一篇文章中提到函数 dm_init_and_scan(bool pre_reloc_only) 中有对设备树节点解析的函数dm_extended_scan_fdt()该函数的主要作用就是扫描设备树中的节点，并创立对应的设备驱动等结构的绑定工作。
先看对应的代码
int dm_extended_scan_fdt(const void *blob, bool pre_reloc_only)
{
ret = dm_scan_fdt(gd->fdt_blob, pre_reloc_only);
//顾名思义，该函数就是扫描设备树并与设备驱动建立联系
ret = dm_scan_fdt_ofnode_path("/clocks", pre_reloc_only);
ret = dm_scan_fdt_ofnode_path("/firmware", pre_reloc_only);
//上面这两个该函数扫描clocks节点和firmware节点
}
重点看第一个函数的具体实现过程
int dm_scan_fdt(const void *blob, bool pre_reloc_only)
{
#if CONFIG_IS_ENABLED(OF_LIVE)
if (of_live_active())
return dm_scan_fdt_live(gd->dm_root, gd->of_root,
pre_reloc_only);
else
#endif
return dm_scan_fdt_node(gd->dm_root, blob, 0, pre_reloc_only);
}
由于没有定义OF_LIVE宏，所以该函数最终调用的是dm_scan_fdt_node函数，那么接下来看该函数的实现过程
tatic int dm_scan_fdt_node(struct udevice *parent, const void *blob,
int offset, bool pre_reloc_only)
{
int ret = 0, err;
//从偏移offset处开始一个个的扫描节点（node）
for (offset = fdt_first_subnode(blob, offset); offset > 0; offset = fdt_next_subnode(blob, offset))
{
const char *node_name = fdt_get_name(blob, offset, NULL);
/*chosen或者firmware节点本身不是一个设备，但是有可能包含其他设备节点，
扫描其子节点*/
if (!strcmp(node_name, "chosen") ||
!strcmp(node_name, "firmware")) {
pr_debug("parsing subnodes of "%s"
", node_name);
err = dm_scan_fdt_node(parent, blob, offset,
pre_reloc_only);
if (err && !ret)
ret = err;
continue;//没有子节点的话则继续扫描下一个节点
}
if (!fdtdec_get_is_enabled(blob, offset)) {//忽略失能设备
pr_debug(" - ignoring disabled device
");
continue;
}
err = lists_bind_fdt(parent, offset_to_ofnode(offset), NULL,
pre_reloc_only);
if (err && !ret) {
ret = err;
debug("%s: ret=%d
", node_name, ret);
}
}
if (ret)
dm_warn("Some drivers failed to bind
");
return ret;
}
int lists_bind_fdt(struct udevice *parent, ofnode node, struct udevice **devp,
bool pre_reloc_only)
{
struct driver *driver = ll_entry_start(struct driver, driver);
const int n_ents = ll_entry_count(struct driver, driver);
const struct udevice_id *id;
struct driver *entry;
struct udevice *dev;
bool found = false;
const char *name, *compat_list, *compat;
int compat_length, i;
int result = 0;
int ret = 0;
if (devp)
*devp = NULL;
name = ofnode_get_name(node);
pr_debug("bind node %s
", name);
compat_list = ofnode_get_property(node, "compatible", &compat_length);
if (!compat_list) {
if (compat_length == -FDT_ERR_NOTFOUND) {
pr_debug("Device '%s' has no compatible string
",
name);
return 0;//这里直接返回，设备能bind的话，需要设备节点有 compatible 属性
}
dm_warn("Device tree error at node '%s'
", name);
return compat_length;
}
//遍历compatible 字符串列表
for (i = 0; i < compat_length; i += strlen(compat) + 1) {
compat = compat_list + i;
pr_debug(" - attempt to match compatible string '%s'
",
compat);
for (entry = driver; entry != driver + n_ents; entry++) {
ret = driver_check_compatible(entry->of_match, &id,
compat);
if (!ret)//遍历driver段表，找到相对应的driver
break;
}
if (entry == driver + n_ents)
continue;
if (pre_reloc_only) {
if (!dm_ofnode_pre_reloc(node) &&
!(entry->flags & DM_FLAG_PRE_RELOC))
return 0;
}
pr_debug(" - found match at '%s'
", entry->name);
ret = device_bind_with_driver_data(parent, entry, name,
id->data, node, &dev);
if (ret == -ENODEV) {
pr_debug("Driver '%s' refuses to bind
", entry->name);
continue;
}
if (ret) {
dm_warn("Error binding driver '%s': %d
", entry->name,
ret);
return ret;
} else {
found = true;
if (devp)
*devp = dev;
}
break;
}
if (!found && !result && ret != -ENODEV)
pr_debug("No match for node '%s'
", name);
return result;
}
函数device_bind_with_driver_data()最终调用的是device_bind_common()函数。
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版权声明：本文为CSDN博主「liuduanfei」的原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.csdn.net/A_orz_/article/details/100657963