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三、深入了解
上一回继续解析platform_device_add函数，没有讲完，本回继续往下讲解。为了便于理解和回顾，再次贴出其源码，在drivers/base/platform.c中，如下：
cpp
/**
* platform_device_add - add a platform device to device hierarchy
* @pdev: platform device we're adding
*
* This is part 2 of platform_device_register(), though may be called
* separately _iff_ pdev was allocated by platform_device_alloc().
*/
int platform_device_add(struct platform_device *pdev)
{
u32 i;
int ret;
if (!pdev)
return -EINVAL;
if (!pdev->dev.parent)
pdev->dev.parent = &platform_bus;
pdev->dev.bus = &platform_bus_type;
switch (pdev->id) {
default:
dev_set_name(&pdev->dev, "%s.%d", pdev->name, pdev->id);
break;
case PLATFORM_DEVID_NONE:
dev_set_name(&pdev->dev, "%s", pdev->name);
break;
case PLATFORM_DEVID_AUTO:
/*
* Automatically allocated device ID. We mark it as such so
* that we remember it must be freed, and we append a suffix
* to avoid namespace collision with explicit IDs.
*/
ret = ida_alloc(&platform_devid_ida, GFP_KERNEL);
if (ret < 0)
goto err_out;
pdev->id = ret;
pdev->id_auto = true;
dev_set_name(&pdev->dev, "%s.%d.auto", pdev->name, pdev->id);
break;
}
for (i = 0; i < pdev->num_resources; i++) {
struct resource *p, *r = &pdev->resource[i];
if (r->name == NULL)
r->name = dev_name(&pdev->dev);
p = r->parent;
if (!p) {
if (resource_type(r) == IORESOURCE_MEM)
p = &iomem_resource;
else if (resource_type(r) == IORESOURCE_IO)
p = &ioport_resource;
}
if (p) {
ret = insert_resource(p, r);
if (ret) {
dev_err(&pdev->dev, "failed to claim resource %d: %pR\n", i, r);
goto failed;
}
}
}
pr_debug("Registering platform device '%s'. Parent at %s\n",
dev_name(&pdev->dev), dev_name(pdev->dev.parent));
ret = device_add(&pdev->dev);
if (ret == 0)
return ret;
failed:
if (pdev->id_auto) {
ida_free(&platform_devid_ida, pdev->id);
pdev->id = PLATFORM_DEVID_AUTO;
}
while (i--) {
struct resource *r = &pdev->resource[i];
if (r->parent)
release_resource(r);
}
err_out:
return ret;
}
EXPORT_SYMBOL_GPL(platform_device_add);上一回在解析platform_device_add函数的时候，讲解到了以下代码片段：
cpp
p = r->parent;
if (!p) {
if (resource_type(r) == IORESOURCE_MEM)
p = &iomem_resource;
else if (resource_type(r) == IORESOURCE_IO)
p = &ioport_resource;
}
if (p) {
ret = insert_resource(p, r);
if (ret) {
dev_err(&pdev->dev, "failed to claim resource %d: %pR\n", i, r);
goto failed;
}
}引出了3个函数：insert_resource()以及其下的insert_resource_conflict()和__insert_resource()。本回开始，对于这3个函数一一进行解析。
（1）insert_resource函数
insert_resource函数在kernel/linux-5.10-origin/kernel/resource.c中，代码如下：
cpp
/**
* insert_resource - Inserts a resource in the resource tree
* @parent: parent of the new resource
* @new: new resource to insert
*
* Returns 0 on success, -EBUSY if the resource can't be inserted.
*
* This function is intended for producers of resources, such as FW modules
* and bus drivers.
*/
int insert_resource(struct resource *parent, struct resource *new)
{
struct resource *conflict;
conflict = insert_resource_conflict(parent, new);
return conflict ? -EBUSY : 0;
}
EXPORT_SYMBOL_GPL(insert_resource);insert_resource函数是Linux内核资源管理核心函数 ，作用是：向内核的全局资源树（resource tree）中注册一段资源（如IOMEM、IOPORT、IRQ、DMA等），防止资源冲突、重复使用。
参数说明：
- struct resource *parent：父资源结点（根资源）。
- struct resouce *new：要插入的新资源。
常用root根资源（内核预定义）：
- &iomem_resource // 物理地址资源（最常用：寄存器、DDR、外设地址）
- &ioport_resource // IO端口资源
- &dma_resource // DMA资源
- &irq_resource // 中断资源
参见上一回定义：
struct resource的定义上一回也给出了，在kernel/linux-5.10-origin/include/linux/ioport.h中，如下：
cpp
/*
* Resources are tree-like, allowing
* nesting etc..
*/
struct resource {
resource_size_t start;
resource_size_t end;
const char *name;
unsigned long flags;
unsigned long desc;
struct resource *parent, *sibling, *child;
};（2）insert_resource_conflict函数
insert_resource_conflict函数也在kernel/linux-5.10-origin/kernel/resource.c中（就在insert_resource函数上边），代码如下：
cpp
/**
* insert_resource_conflict - Inserts resource in the resource tree
* @parent: parent of the new resource
* @new: new resource to insert
*
* Returns 0 on success, conflict resource if the resource can't be inserted.
*
* This function is equivalent to request_resource_conflict when no conflict
* happens. If a conflict happens, and the conflicting resources
* entirely fit within the range of the new resource, then the new
* resource is inserted and the conflicting resources become children of
* the new resource.
*
* This function is intended for producers of resources, such as FW modules
* and bus drivers.
*/
struct resource *insert_resource_conflict(struct resource *parent, struct resource *new)
{
struct resource *conflict;
write_lock(&resource_lock);
conflict = __insert_resource(parent, new);
write_unlock(&resource_lock);
return conflict;
}由代码可见，此函数只是完成了外层的加解锁，而把实际的工作交给了__insert_resource函数。
__insert_resource函数就在insert_resource_conflict函数的上边，代码如下：
cpp
/*
* Insert a resource into the resource tree. If successful, return NULL,
* otherwise return the conflicting resource (compare to __request_resource())
*/
static struct resource * __insert_resource(struct resource *parent, struct resource *new)
{
struct resource *first, *next;
for (;; parent = first) {
first = __request_resource(parent, new);
if (!first)
return first;
if (first == parent)
return first;
if (WARN_ON(first == new)) /* duplicated insertion */
return first;
if ((first->start > new->start) || (first->end < new->end))
break;
if ((first->start == new->start) && (first->end == new->end))
break;
}
for (next = first; ; next = next->sibling) {
/* Partial overlap? Bad, and unfixable */
if (next->start < new->start || next->end > new->end)
return next;
if (!next->sibling)
break;
if (next->sibling->start > new->end)
break;
}
new->parent = parent;
new->sibling = next->sibling;
new->child = first;
next->sibling = NULL;
for (next = first; next; next = next->sibling)
next->parent = new;
if (parent->child == first) {
parent->child = new;
} else {
next = parent->child;
while (next->sibling != first)
next = next->sibling;
next->sibling = new;
}
return NULL;
}对于__insert_resource函数的解析，请看下回。