如同Linux Kernel（15.3）- The Linux usage model for device tree data所描述，init_machine()透過呼叫of_platform_populate()建構platform device。
kernel v3.5
|-->> msm8x60_dt_init(void) @arch/arm/mach-msm/board-msm8x60.c
|--> of_platform_populate() @drivers/of/platform.c
|--> of_platform_bus_create() @drivers/of/platform.c
/* Make sure it has a compatible property */
那些具有compatible的node都會被轉成platform device
if (strict && (!of_get_property(bus, "compatible", NULL))) {
pr_debug("%s() - skipping %s, no compatible prop\n",
__func__, bus->full_name);
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;
}
}
接著會在註冊driver時, 呼叫of_driver_match_device()進行match
kernel v3.5
|--> platform_driver_register() @drivers/base/platform.c
|--> driver_register() @drivers/base/driver.c
|--> bus_add_driver() @drivers/base/bus.c /* 建立sysfs file node 與 attr */
|--> driver_attach() @drivers/base/dd.c
|--> bus_for_each_dev(drv->bus, NULL, drv, __driver_attach) @bus.c
|--> __driver_attach @drivers/base/dd.c
|--> driver_match_device(drv, dev) @base.h
|--> platform_match(); @drivers/base/platform.c
if (of_driver_match_device(dev, drv))
return 1;
|--> __driver_attach @drivers/base/dd.c
if (!dev->driver)
driver_probe_device(drv, dev);
|--> driver_probe_device @drivers/base/dd.c
ret = really_probe(dev, drv);
|--> really_probe @drivers/base/dd.c
if (dev->bus->probe) {
ret = dev->bus->probe(dev);
if (ret)
goto probe_failed;
} else if (drv->probe) {
ret = drv->probe(dev);
if (ret)
goto probe_failed;
}
----- @include/linux/of_device.h -----
of_driver_match_device(struct device *dev, const struct device_driver *drv)
{
return of_match_device(drv->of_match_table, dev) != NULL;
}
----- @drivers/of/device.c -----
const struct of_device_id *of_match_device(const struct of_device_id *matches,
const struct device *dev)
{
if ((!matches) || (!dev->of_node))
return NULL;
return of_match_node(matches, dev->of_node);
}
----- @drivers/of/base.c -----
const struct of_device_id *of_match_node(const struct of_device_id *matches,
const struct device_node *node)
{
if (!matches)
return NULL;
while (matches->name[0] || matches->type[0] || matches->compatible[0]) {
int match = 1;
if (matches->name[0])
match &= node->name && !strcmp(matches->name, node->name);
if (matches->type[0])
match &= node->type && !strcmp(matches->type, node->type);
if (matches->compatible[0])
match &= of_device_is_compatible(node, matches->compatible);
if (match)
return matches;
matches++;
}
return NULL;
}
修改一下DTS驗證一下platform device
/ {
node1 {
compatible = "brook,dts1";
a-string-property = "A string";
a-string-list-property = "first string", "second string";
// hex is implied in byte arrays. no '0x' prefix is required
a-byte-data-property = [01 23 34 56];
child-node1 {
first-child-property;
second-child-property = <1>;
a-string-property = "Hello, world";
};
child-node2 {
};
};
};
/ # ls /sys/bus/platform/devices 10000000.sysreg 10002000.i2c ... node1 ... / # cd /sys/bus/platform/devices/node1/ /sys/devices/platform/node1 # ls driver_override of_node subsystem modalias power uevent /sys/devices/platform/node1 # ls of_node/ a-byte-data-property child-node1 name a-string-list-property child-node2 a-string-property compatible /sys/devices/platform/node1 # ftpget 192.168.1.1 /tmp/brook_modules.ko /home/brook/my_driver/brook_modules.ko /sys/devices/platform/node1 # insmod /tmp/brook_modules.ko brook_modules: loading out-of-tree module taints kernel. brook_init(#55) brook_probe(#21)
基本上與傳統的platform device driver的差異是:
- device由DTS的compatible產生，無須呼叫platform_device_register()註冊device
- 需在platform_driver.driver.of_match_table中掛上of_device_id[]，裡面的compatible會與DTS的compatible進行比對
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/of.h>
#include <linux/of_device.h>
MODULE_AUTHOR("Brook");
MODULE_DESCRIPTION("Kernel module for demo");
MODULE_LICENSE("GPL");
#define DEVNAME "brook"
static struct platform_device brook_device = {
.name = DEVNAME,
};
static int brook_probe(struct platform_device *pdev)
{
pr_info("%s(#%d)\n", __func__, __LINE__);
return 0;
}
static int brook_remove(struct platform_device *pdev)
{
pr_info("%s(#%d)\n", __func__, __LINE__);
return 0;
}
static struct of_device_id brook_dt_ids[] = {
{
.compatible = "brook,dts1",
}, {
.compatible = "brook,dts2",
}, {
}
};
MODULE_DEVICE_TABLE(of, brook_dt_ids);
static struct platform_driver brook_driver = {
.driver = {
.name = DEVNAME,
.owner = THIS_MODULE,
.of_match_table = brook_dt_ids,
},
.probe = brook_probe,
.remove = brook_remove,
};
static int __init brook_init(void)
{
int ret;
pr_info("%s(#%d)\n", __func__, __LINE__);
ret = platform_driver_register(&brook_driver);
if (ret) {
dev_err(&(brook_device.dev),
"%s(#%d): platform_driver_register fail(%d)\n", __func__,
__LINE__, ret);
}
return ret;
}
module_init(brook_init);
static void __exit brook_exit(void)
{
dev_info(&(brook_device.dev), "%s(#%d)\n", __func__, __LINE__);
platform_driver_unregister(&brook_driver);
}
module_exit(brook_exit);
-
參考資料:
- http://wiki.dreamrunner.org/public_html/Embedded-System/Linux-Device-Tree.html, Linux Device tree
- Linux Kernel（15.3）- The Linux usage model for device tree data
- http://wiki.100ask.org/%E7%AC%AC%E4%B8%89%E8%AF%BE:%E5%86%85%E6%A0%B8%E5%AF%B9%E8%AE%BE%E5%A4%87%E6%A0%91%E7%9A%84%E5%A4%84%E7%90%86, 内核对设备树的处理
