3.x版本内核中platform_device的生成
内核版本：Linux-3.18.2
在3.x版本内核中platform_device不再静态定义，而是通过device tree来动态生成，例如（arch/arm/mach-s3c24xx/mach-sc2416-dt.c）：
static void __init s3c2416_dt_machine_init(void)
{
of_platform_populate(NULL, of_default_bus_match_table, NULL, NULL);
s3c_pm_init();
}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;
for_each_child_of_node(root, child) {
rc = of_platform_bus_create(child, matches, lookup, parent, true);
if (rc)
break;
}
of_node_put(root);
return rc;
}如果传递进来的参数root为NULL，那么需要通过of_find_node_by_path函数找到device tree中的根节点。
得到根节点之后呢，就需要通过这个根节点来遍历device tree中的节点了。得到一个子节点之后，调用of_platform_bus_create函数：
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 */
if (strict && (!of_get_property(bus, "compatible", NULL))) {
pr_debug("%s() - skipping %s, no compatible prop\n",
__func__, bus->full_name);
return 0;
}
auxdata = of_dev_lookup(lookup, bus);
if (auxdata) {
bus_id = auxdata->name;
platform_data = auxdata->platform_data;
}
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;
}
dev = of_platform_device_create_pdata(bus, bus_id, platform_data, parent);
if (!dev || !of_match_node(matches, bus))
return 0;
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;
}所幸在mach-sc2416-dt.c中传递进来的lookup参数为NULL，所以of_dev_lookup这部分也就不去看了。
如果"compatible"属性值有"arm,primecell"，则会调用of_amba_device_create函数去创建amba_device，这个设备暂时也不知道是一个什么设备，那么这里还是先忽略。
继续，调用of_platform_device_create_pdata函数：
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;
if (!of_device_is_available(np) ||
of_node_test_and_set_flag(np, OF_POPULATED))
return NULL;
dev = of_device_alloc(np, bus_id, parent);
if (!dev)
goto err_clear_flag;
of_dma_configure(&dev->dev);
dev->dev.bus = &platform_bus_type;
dev->dev.platform_data = platform_data;
/* We do not fill the DMA ops for platform devices by default.
* This is currently the responsibility of the platform code
* to do such, possibly using a device notifier
*/
if (of_device_add(dev) != 0) {
platform_device_put(dev);
goto err_clear_flag;
}
return dev;
err_clear_flag:
of_node_clear_flag(np, OF_POPULATED);
return NULL;
}首先调用of_device_is_available函数，这个函数主要是用于检测"status"属性的，如果没有"status"属性，那还好说直接返回true。如果有"status"属性，而它的值又不是"okay"或"ok"，那么不好意思，返回false，否则还是返回true。所以"status"属性就是用来检测是否可用（有点拗口，其实就是用来确认是否需要创建platform设备）。
"status"属性检测完毕了，则要调用of_device_alloc函数来为platform_device分配内存了。
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;
dev = platform_device_alloc("", -1);
if (!dev)
return NULL;
/* count the io and irq resources */
while (of_address_to_resource(np, num_reg, &temp_res) == 0)
num_reg++;
num_irq = of_irq_count(np);
/* Populate the resource table */
if (num_irq || num_reg) {
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;
for (i = 0; i < num_reg; i++, res++) {
rc = of_address_to_resource(np, i, res);
WARN_ON(rc);
}
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);
}
dev->dev.of_node = of_node_get(np);
dev->dev.parent = parent;
if (bus_id)
dev_set_name(&dev->dev, "%s", bus_id);
else
of_device_make_bus_id(&dev->dev);
return dev;
}内存申请了之后，还会对platform_device做一些初始化，例如IO、中断资源等等。首先是调用of_address_to_resource和of_irq_count去计算io和中断资源的个数（有注释说明）。
int of_address_to_resource(struct device_node *dev, int index,
struct resource *r)
{
const __be32 *addrp;
u64 size;
unsigned int flags;
const char *name = NULL;
addrp = of_get_address(dev, index, &size, &flags);
if (addrp == NULL)
return -EINVAL;
/* Get optional "reg-names" property to add a name to a resource */
of_property_read_string_index(dev, "reg-names", index, &name);
return __of_address_to_resource(dev, addrp, size, flags, name, r);
}const __be32 *of_get_address(struct device_node *dev, int index, u64 *size,
unsigned int *flags)
{
const __be32 *prop;
unsigned int psize;
struct device_node *parent;
struct of_bus *bus;
int onesize, i, na, ns;
/* Get parent & match bus type */
parent = of_get_parent(dev);
if (parent == NULL)
return NULL;
bus = of_match_bus(parent);
bus->count_cells(dev, &na, &ns);
of_node_put(parent);
if (!OF_CHECK_ADDR_COUNT(na))
return NULL;
/* Get "reg" or "assigned-addresses" property */
prop = of_get_property(dev, bus->addresses, &psize);
if (prop == NULL)
return NULL;
psize /= 4;
onesize = na + ns;
for (i = 0; psize >= onesize; psize -= onesize, prop += onesize, i++)
if (i == index) {
if (size)
*size = of_read_number(prop + na, ns);
if (flags)
*flags = bus->get_flags(prop);
return prop;
}
return NULL;
}static struct of_bus *of_match_bus(struct device_node *np)
{
int i;
for (i = 0; i < ARRAY_SIZE(of_busses); i++)
if (!of_busses[i].match || of_busses[i].match(np))
return &of_busses[i];
BUG();
return NULL;
}static struct of_bus of_busses[] = {
#ifdef CONFIG_OF_ADDRESS_PCI
/* PCI */
{
.name = "pci",
.addresses = "assigned-addresses",
.match = of_bus_pci_match,
.count_cells = of_bus_pci_count_cells,
.map = of_bus_pci_map,
.translate = of_bus_pci_translate,
.get_flags = of_bus_pci_get_flags,
},
#endif /* CONFIG_OF_ADDRESS_PCI */
/* ISA */
{
.name = "isa",
.addresses = "reg",
.match = of_bus_isa_match,
.count_cells = of_bus_isa_count_cells,
.map = of_bus_isa_map,
.translate = of_bus_isa_translate,
.get_flags = of_bus_isa_get_flags,
},
/* Default */
{
.name = "default",
.addresses = "reg",
.match = NULL,
.count_cells = of_bus_default_count_cells,
.map = of_bus_default_map,
.translate = of_bus_default_translate,
.get_flags = of_bus_default_get_flags,
},
};回到of_get_address函数中，调用of_get_property函数去读取哪个属性呢，就是前面的addresses值的属性，即reg属性，所以reg属性就是用来定义io地址地址信息的。而io地址的长度是通过of_get_address中的of_read_number去读取完成的，最后返回这个io地址。
回到of_address_to_resource函数中，在得到这个io地址之后，调用__of_address_to_resource函数将io地址转换成struct resource资源信息。
然后是中断资源。
int of_irq_count(struct device_node *dev)
{
struct of_phandle_args irq;
int nr = 0;
while (of_irq_parse_one(dev, nr, &irq) == 0)
nr++;
return nr;
}
int of_irq_parse_one(struct device_node *device, int index, struct of_phandle_args *out_irq)
{
struct device_node *p;
const __be32 *intspec, *tmp, *addr;
u32 intsize, intlen;
int i, res = -EINVAL;
pr_debug("of_irq_parse_one: dev=%s, index=%d\n", of_node_full_name(device), index);
/* OldWorld mac stuff is "special", handle out of line */
if (of_irq_workarounds & OF_IMAP_OLDWORLD_MAC)
return of_irq_parse_oldworld(device, index, out_irq);
/* Get the reg property (if any) */
addr = of_get_property(device, "reg", NULL);
/* Try the new-style interrupts-extended first */
res = of_parse_phandle_with_args(device, "interrupts-extended",
"#interrupt-cells", index, out_irq);
if (!res)
return of_irq_parse_raw(addr, out_irq);
/* Get the interrupts property */
intspec = of_get_property(device, "interrupts", &intlen);
if (intspec == NULL)
return -EINVAL;
intlen /= sizeof(*intspec);
pr_debug(" intspec=%d intlen=%d\n", be32_to_cpup(intspec), intlen);
/* Look for the interrupt parent. */
p = of_irq_find_parent(device);
if (p == NULL)
return -EINVAL;
/* Get size of interrupt specifier */
tmp = of_get_property(p, "#interrupt-cells", NULL);
if (tmp == NULL)
goto out;
intsize = be32_to_cpu(*tmp);
pr_debug(" intsize=%d intlen=%d\n", intsize, intlen);
/* Check index */
if ((index + 1) * intsize > intlen)
goto out;
/* Copy intspec into irq structure */
intspec += index * intsize;
out_irq->np = p;
out_irq->args_count = intsize;
for (i = 0; i < intsize; i++)
out_irq->args[i] = be32_to_cpup(intspec++);
/* Check if there are any interrupt-map translations to process */
res = of_irq_parse_raw(addr, out_irq);
out:
of_node_put(p);
return res;
}回到of_device_alloc函数，还是通过前面的of_address_to_resource函数将io地址资源赋值给平台设备，通过of_irq_to_resource_table函数将中断号转换成中断资源信息并赋值给平台设备。
int of_irq_to_resource_table(struct device_node *dev, struct resource *res,
int nr_irqs)
{
int i;
for (i = 0; i < nr_irqs; i++, res++)
if (!of_irq_to_resource(dev, i, res))
break;
return i;
}
int of_irq_to_resource(struct device_node *dev, int index, struct resource *r)
{
int irq = irq_of_parse_and_map(dev, index);
/* Only dereference the resource if both the
* resource and the irq are valid. */
if (r && irq) {
const char *name = NULL;
memset(r, 0, sizeof(*r));
/*
* Get optional "interrupt-names" property to add a name
* to the resource.
*/
of_property_read_string_index(dev, "interrupt-names", index,
&name);
r->start = r->end = irq;
r->flags = IORESOURCE_IRQ | irqd_get_trigger_type(irq_get_irq_data(irq));
r->name = name ? name : of_node_full_name(dev);
}
return irq;
}
回到of_platform_device_create_pdata函数中，平台设备已经申请好了，然后对平台设备继续进行赋值操作，例如平台设备的总线赋值为平台总线，平台设备的私有数据赋值为platform_data，最后调用of_device_add函数将平台设备注册到内核中。
总结，涉及到的属性有： "compatible" 必须 "status" 可选属性 "reg" io资源 "interrupts" 中断资源