在前面學(xué)習(xí)了 kobject和 kset之后，就迫不及待的想開始“研究”設(shè)備模型了。經(jīng)過這幾天的學(xué)習(xí)，感覺受益匪淺。所以就將自己的理解整理了下來
想要完成一個(gè)設(shè)備的驅(qū)動(dòng)，就要涉及三部分: Bus, device, driver。當(dāng)然這些“新”節(jié)點(diǎn)都是最終繼承于kobject。
一.Bus
這里先整理一下BUS，總線負(fù)責(zé)在設(shè)備與驅(qū)動(dòng)間建立連接，包括 I2C, PCI, 串口，platform等。其中platform是虛擬總線。
1.1 結(jié)構(gòu)體
信息結(jié)構(gòu)體是 bus_type.
struct bus_type {
const char *name; //the name of bus
struct bus_attribute *bus_attrs;
//attribute for bus, contain attribute file and some operate function.
// this is a interface between kernel space and user space.
struct device_attribute *dev_attrs; //attribute for device,
struct driver_attribute *drv_attrs; //attribute for deriver
int (*match)(struct device *dev, struct device_driver *drv);
int (*uevent)(struct device *dev, struct kobj_uevent_env *env);
int (*probe)(struct device *dev);
int (*remove)(struct device *dev);
void (*shutdown)(struct device *dev);
int (*suspend)(struct device *dev, pm_message_t state);
int (*suspend_late)(struct device *dev, pm_message_t state);
int (*resume_early)(struct device *dev);
int (*resume)(struct device *dev);
struct dev_pm_ops *pm; //power manage
struct bus_type_private *p;
//private data for bus. In fact, it is core of this structure
};
在其中 bus_attrs, dev_attrs 和 drv_attrs記錄了該總線的一些屬性信息，而最重要的被用來構(gòu)建該總線的邏輯結(jié)構(gòu)的信息都記錄在了bus_type_private中。對應(yīng)這個(gè)總線私有數(shù)據(jù)結(jié)構(gòu)體的解析如下。
struct bus_type_private {
struct kset subsys;
//there are two points:
//1).this is a set. It is contain some devices and derivers about this bus.
//2). it's parent is @bus_kset, which is the root of all other bus.@bus_kset have many subset, this is just one of them.
//
struct kset *drivers_kset;
//all drivers about this bus will belong to this set.
struct kset *devices_kset;
//all devices of this bus will belong to this set.
struct klist klist_devices;
struct klist klist_drivers;
//they are two lists , for mount all corresponding nodes.
struct blocking_notifier_head bus_notifier;
unsigned int drivers_autoprobe:1;
//is this bus automaticly run when a new devices arrvied.
//sometime, we can see some attribute files in user space.(for example:@drivers_autoprobe).
//it is interface that kernel leave user to modify this argument.
struct bus_type *bus;
//just a port for return this bus.
};
其中的klist_devices, klist_drivers 鏈表會(huì)用來掛載該總線的設(shè)備與驅(qū)動(dòng)。當(dāng)需要找東西的時(shí)候就會(huì)去倆面翻。而上面的兩個(gè)kset 分別是它們所屬的集合。不同的集合對應(yīng)于不同的操作特性。這是一種很給力的組織結(jié)構(gòu)。就拿這里來說，我們用kobject來組織了一個(gè)二維鏈表(或其他什么數(shù)據(jù)結(jié)構(gòu))，每個(gè)kobject在這個(gè)鏈表中充當(dāng)了一個(gè)節(jié)點(diǎn)。但又想讓其中指定的一些kobject節(jié)點(diǎn)具有一些屬性。kset相當(dāng)于kobject的屬性。它包含了進(jìn)行事件通知需要的一些數(shù)據(jù)信息。每當(dāng)kobject有需要時(shí)，就會(huì)去找到自己所屬的kset,或者上級kobject的kset來用。
1.2 重要函數(shù)分析
對于總線的注冊需要使用到如下函數(shù)，通過分析它的行為對于理解bus_type的邏輯結(jié)構(gòu)是很有幫助。
/**
* bus_register - register a bus with the system.
* @bus: bus.
*
* Once we have that, we registered the bus with the kobject
* infrastructure, then register the children subsystems it has:
* the devices and drivers that belong to the bus.
*/
int bus_register(struct bus_type *bus)
{
int retval;
struct bus_type_private *priv;
//alloc a private data package for @bus. It is the core of this structure,
//include device list, deriver list and so on.
priv = kzalloc(sizeof(struct bus_type_private), GFP_KERNEL);
if (!priv)
return -ENOMEM;
priv->bus = bus;
bus->p = priv;
BLOCKING_INIT_NOTIFIER_HEAD(&priv->bus_notifier);
// before we keep on, what we should to know is that this bus is one of members of the great building,
//so it must be inherit form @kobject.
//and @(priv->subsys.kobj) is it's kobject.
retval = kobject_set_name(&priv->subsys.kobj, "%s", bus->name);
if (retval)
goto out;
priv->subsys.kobj.kset = bus_kset; //1).@bus_kset is the root of all buses. 2). this structure is the type of bus.
priv->subsys.kobj.ktype = &bus_ktype; //corresponding operation function for bus
priv->drivers_autoprobe = 1; //automaticly probe when new device arrived.
retval = kset_register(&priv->subsys);
if (retval)
goto out;
retval = bus_create_file(bus, &bus_attr_uevent); //create attribute file for bus,it is a interface between user space and kernel space.
if (retval)
goto bus_uevent_fail;
//給該總線創(chuàng)建一個(gè)設(shè)備子集,it is the set of all devices about this bus.
//在文件系統(tǒng)中的表現(xiàn)就是在該總線的目錄下多了一個(gè)名字叫"devices"的子目錄
//還需要提醒的一點(diǎn)就是:設(shè)備模型中的層次結(jié)構(gòu)關(guān)系都是由kobject對象來指定，所以凡是屬于這個(gè)設(shè)備模型的節(jié)點(diǎn)必須要繼承kobject.
priv->devices_kset = kset_create_and_add("devices", NULL,
&priv->subsys.kobj);
if (!priv->devices_kset) {
retval = -ENOMEM;
goto bus_devices_fail;
}
//create a deriver set for this bus
priv->drivers_kset = kset_create_and_add("drivers", NULL,
&priv->subsys.kobj);
if (!priv->drivers_kset) {
retval = -ENOMEM;
goto bus_drivers_fail;
}
//thoes two list is used to mount some nodes. device-node or deriver-node.
klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put);
klist_init(&priv->klist_drivers, NULL, NULL);
//create attribute file for this structure
retval = add_probe_files(bus);
if (retval)
goto bus_probe_files_fail;
retval = bus_add_attrs(bus); //create attribute file for @bus_attr
if (retval)
goto bus_attrs_fail;
pr_debug("bus: '%s': registeredn", bus->name);
return 0;
bus_attrs_fail:
remove_probe_files(bus);
bus_probe_files_fail:
kset_unregister(bus->p->drivers_kset);
bus_drivers_fail:
kset_unregister(bus->p->devices_kset);
bus_devices_fail:
bus_remove_file(bus, &bus_attr_uevent);
bus_uevent_fail:
kset_unregister(&bus->p->subsys);
kfree(bus->p);
out:
bus->p = NULL;
return retval;
}
在函數(shù)體中已經(jīng)對行為進(jìn)行了較詳細(xì)的分析。
1.3 device_bind_driver
那么device到底又是怎么和一個(gè)driver進(jìn)行綁定的呢?讓它們在需要時(shí)能找到彼此
//bind a driver to one device.
int device_bind_driver(struct device *dev)
{
int ret;
ret = driver_sysfs_add(dev);
if (!ret)
driver_bound(dev);
return ret;
}
//這個(gè)函數(shù)是在設(shè)備已經(jīng)綁定驅(qū)動(dòng)之后使用，
static void driver_bound(struct device *dev)
{
if (klist_node_attached(&dev->p->knode_driver)) {
printk(KERN_WARNING "%s: device %s already boundn",
__func__, kobject_name(&dev->kobj));
return;
}
pr_debug("driver: '%s': %s: bound to device '%s'n", dev_name(dev),
__func__, dev->driver->name);
if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_BOUND_DRIVER, dev);
//把設(shè)備節(jié)點(diǎn)加入驅(qū)動(dòng)的節(jié)點(diǎn)鏈表中
//?既然設(shè)備已經(jīng)能找到自己的驅(qū)動(dòng)了，為什么還需要加入驅(qū)動(dòng)的鏈表
//?一個(gè)驅(qū)動(dòng)可能支持一組設(shè)備，對于那些邏輯操作相同的設(shè)備,所有驅(qū)動(dòng)有一個(gè)設(shè)備鏈表
klist_add_tail(&dev->p->knode_driver, &dev->driver->p->klist_devices);
}
二. 設(shè)備信息
2.1 信息結(jié)構(gòu)體
在總線的其中一端掛載的是設(shè)備。其用于記錄數(shù)據(jù)和操作的結(jié)構(gòu)體是device.
struct device {
struct device *parent; //parent device
struct device_private *p; //private data for device, 包含了其拓?fù)浣Y(jié)構(gòu)信息
struct kobject kobj;
//@device is inherit from @kobject. so it is belong to @devices_kset, which is created by kernel for devices and contain of some operation functions for devices.
//devices_kset
const char *init_name; /* initial name of the device */
struct device_type *type;
struct semaphore sem; /* semaphore to synchronize calls to
* its driver.
*/
struct bus_type *bus; /* type of bus device is on */
struct device_driver *driver; /* which driver has allocated this
device */
void *driver_data; /* data private to the driver */
void *platform_data; /* Platform specific data, device
core doesn't touch it */
struct dev_pm_info power;
#ifdef CONFIG_NUMA
int numa_node; /* NUMA node this device is close to */
#endif
u64 *dma_mask; /* dma mask (if dma'able device) */
u64 coherent_dma_mask;/* Like dma_mask, but for
alloc_coherent mappings as
not all hardware supports
64 bit addresses for consistent
allocations such descriptors. */
struct device_dma_parameters *dma_parms;
struct list_head dma_pools; /* dma pools (if dma'ble) */
struct dma_coherent_mem *dma_mem; /* internal for coherent mem
override */
/* arch specific additions */
struct dev_archdata archdata;
dev_t devt; /* dev_t, creates the sysfs "dev" */
spinlock_t devres_lock;
struct list_head devres_head;
struct klist_node knode_class;
struct class *class;
struct attribute_group **groups; /* optional groups */
void (*release)(struct device *dev);
};
而這個(gè)節(jié)點(diǎn)的拓?fù)浣Y(jié)構(gòu)信息則保存在 device_private 中
struct device_private {
struct klist klist_children;
//klist containing all children of this device
struct klist_node knode_parent;
//node in sibling list
struct klist_node knode_driver;
//node in driver list, @device is mount on the list of driver by this member.
//In linux system, one device have only one driver.
//But it is not same as to driver, one driver may have a lot of devices, if only those device have a same logical operation.
struct klist_node knode_bus;
//apparently, this device is need to mount on the list of bus, too.
struct device *device;
//point to this device
};
2.2 重要函數(shù)
設(shè)備的注冊函數(shù)為 device_register( ), 其會(huì)建立設(shè)備的拓?fù)潢P(guān)系，并將設(shè)備添加到對應(yīng)總線的拓?fù)淞斜碇小?/p>
int device_register(struct device *dev)
{
device_initialize(dev);
return device_add(dev);
}