一、spi总线注册

这里所说的SPI核心，就是指/drivers/spi/目录下spi.c文件中提供给其他文件的函数，首先看下spi核心的初始化函数spi_init(void)。程序如下：

点击(此处)折叠或打开

static int __init spi_init(void)
{
int status;
buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);
if (!buf) {
status = -ENOMEM;
goto err0;
}
status = bus_register(&spi_bus_type);
if (status < 0)
goto err1;
status = class_register(&spi_master_class);
if (status < 0)
goto err2;
return 0;
err2:
bus_unregister(&spi_bus_type);
err1:
kfree(buf);
buf = NULL;
err0:
return status;
}
postcore_initcall(spi_init);

说明：
1) 由postcore_initcall(spi_init);可以看出，此宏在系统初始化时是先于module_init()执行的。

2) 申请的buf空间用于在spi数据传输中。

3) 接下来是总线注册和类注册，首先看下总线注册。

点击(此处)折叠或打开

struct subsys_private {
struct kset subsys;
struct kset *devices_kset;
struct kset *drivers_kset;
struct klist klist_devices;
struct klist klist_drivers;
struct blocking_notifier_head bus_notifier;
unsigned int drivers_autoprobe:1;
struct bus_type *bus;
struct list_head class_interfaces;
struct kset glue_dirs;
struct mutex class_mutex;
struct class *class;
};
struct bus_type {
const char *name;
struct bus_attribute *bus_attrs;
struct device_attribute *dev_attrs;
struct driver_attribute *drv_attrs;
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 (*resume)(struct device *dev);
const struct dev_pm_ops *pm;
struct subsys_private *p;
};
struct bus_type spi_bus_type = {
.name = "spi",
.dev_attrs = spi_dev_attrs,
.match = spi_match_device,
.uevent = spi_uevent,
.pm = &spi_pm,
};
int bus_register(struct bus_type *bus)
{
int retval;
struct subsys_private *priv;
priv = kzalloc(sizeof(struct subsys_private), GFP_KERNEL);
if (!priv)
return -ENOMEM;
priv->bus = bus;
bus->p = priv;
BLOCKING_INIT_NOTIFIER_HEAD(&priv->bus_notifier);
//总线的名字”spi”,我们说过了一个kobject对应一个目录，这里为这个目录赋值名字
retval = kobject_set_name(&priv->subsys.kobj, "%s", bus->name);
if (retval)
goto out;
priv->subsys.kobj.kset = bus_kset;
priv->subsys.kobj.ktype = &bus_ktype;
priv->drivers_autoprobe = 1;
//创建devices命名的目录
retval = kset_register(&priv->subsys);
if (retval)
goto out;
//创建属性文件
retval = bus_create_file(bus, &bus_attr_uevent);
if (retval)
goto bus_uevent_fail;
priv->devices_kset = kset_create_and_add("devices", NULL,
&priv->subsys.kobj);
if (!priv->devices_kset) {
retval = -ENOMEM;
goto bus_devices_fail;
}
priv->drivers_kset = kset_create_and_add("drivers", NULL,
&priv->subsys.kobj);
if (!priv->drivers_kset) {
retval = -ENOMEM;
goto bus_drivers_fail;
}
klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put);
klist_init(&priv->klist_drivers, NULL, NULL);
retval = add_probe_files(bus); //添加探测属性
if (retval)
goto bus_probe_files_fail;
retval = bus_add_attrs(bus); //添加其他属性
if (retval)
goto bus_attrs_fail;
pr_debug("bus: '%s': registered\n", 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);
out:
kfree(bus->p);
bus->p = NULL;
return retval;
}

说明：

1) 首先不管是设备还是驱动，都是挂接在某条总线上的，也就是说我们根据总线类型的不同来区分各种设备和驱动。

2) 从总线注册函数bus_register(struct bus_type *bus)中可以发现，首先申请了一个subsys_private结构体内存。该结构体中包含了三个kset结构，分别是struct kset subsys、struct kset *devices_kset和struct kset *drivers_kset。

3) subsys是用来向上链接的。

4) 当发现一个设备或者驱动的时候，对于每一次设备或者驱动注册(设备是被插入了，驱动就是.ko模块被加载)，都得分配一个device或者device_drive结构，每一次都需要将device结构挂入drivers或devices(kset结构)链表中，这样才能通过总线找到挂接在这个总线上的所有设备和驱动。这里仅仅将设备和驱动挂接在总线上，并不能表明设备和驱动之间的关系，这样的处理仅仅表明了驱动、设备与总线的关系，它们申明了我现在挂接在这条总线上，以后操作我就通过这条总线。

5) 总线的目录名为”spi”。也就是说在/sys/bus目录下有一个spi目录，即。内核中有spi总线驱动，bus_register(&spi_bus_type)就是用来注册总线的，该函数调用完成后，就会在/sys/bus/目录下创建spi目录。

接下来看下总线中spi_match_device()函数，此函数在(四)中的设备注册中会调用，如下：

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static int spi_match_device(struct device *dev, struct device_driver *drv)
{
const struct spi_device *spi = to_spi_device(dev);
const struct spi_driver *sdrv = to_spi_driver(drv);
/* Attempt an OF style match */
if (of_driver_match_device(dev, drv))
return 1;
if (sdrv->id_table)
return !!spi_match_id(sdrv->id_table, spi);
return strcmp(spi->modalias, drv->name) == 0;
}

说明：

1) 首先查看驱动和设备是否匹配，如果不匹配，退出。

2) 判断驱动中是否支持id数组，如果支持，查找匹配此id的spi_device。

3) 比较设备的名字的和驱动的名字是否相同。

二、spi驱动注册

在《Linux spi驱动分析(四)----SPI设备驱动(W25Q32BV)》中，执行语句spi_register_driver(&w25q_driver);，从而注册spi驱动。函数如下：

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struct spi_driver {
const struct spi_device_id *id_table;
int (*probe)(struct spi_device *spi);
int (*remove)(struct spi_device *spi);
void (*shutdown)(struct spi_device *spi);
int (*suspend)(struct spi_device *spi, pm_message_t mesg);
int (*resume)(struct spi_device *spi);
struct device_driver driver;
};
static struct spi_driver w25q_driver = {
.driver = {
.name = "spi-w25q",
.owner = THIS_MODULE,
},
//.id_table = w25q_ids,
.probe = w25q_probe,
.remove = __devexit_p(w25q_remove),
};
int spi_register_driver(struct spi_driver *sdrv)
{
sdrv->driver.bus = &spi_bus_type;
if (sdrv->probe)
sdrv->driver.probe = spi_drv_probe;
if (sdrv->remove)
sdrv->driver.remove = spi_drv_remove;
if (sdrv->shutdown)
sdrv->driver.shutdown = spi_drv_shutdown;
return driver_register(&sdrv->driver);
}

说明：

1) 驱动是如何插入到/sys/bus/drivers/spi目录下的？在driver_register->driver_register->bus_add_driver函数中有个重要的语句drv->kobj.kset = &bus->drivers，这里就是将driver的kobj所属的kset挂接上总线的kset。

2) 在struct spi_driver中指明驱动的名称，这里是"spi-w25q"。

3) spi_register_driver()函数的参数为spi_driver结构。函数定义了bus_type，也就是驱动挂接的总线类型。函数接下来对结构体spi_driver中的device_driver成员赋值。

4) 驱动注册，程序如下：

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struct device_driver {
const char *name; //设备驱动的名字
struct bus_type *bus; //设备驱动挂接的总线类型
struct module *owner;
const char *mod_name; /* used for built-in modules */
bool suppress_bind_attrs; /* disables bind/unbind via sysfs */
const struct of_device_id *of_match_table;
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 (*resume) (struct device *dev);
const struct attribute_group **groups;
const struct dev_pm_ops *pm;
struct driver_private *p;
};
int driver_register(struct device_driver *drv)
{
int ret;
struct device_driver *other;
BUG_ON(!drv->bus->p);
if ((drv->bus->probe && drv->probe) ||
(drv->bus->remove && drv->remove) ||
(drv->bus->shutdown && drv->shutdown))
printk(KERN_WARNING "Driver '%s' needs updating - please use "
"bus_type methods\n", drv->name);
/* 在kobject结构组成的链表中查找是否已经存在这个驱动,前面讲过,驱动必然挂接在某个总线
上，返回值是device_driver结构的指针 */
other = driver_find(drv->name, drv->bus);
if (other) {
put_driver(other);
printk(KERN_ERR "Error: Driver '%s' is already registered, "
"aborting...\n", drv->name);
return -EBUSY;
}
ret = bus_add_driver(drv);
if (ret)
return ret;
ret = driver_add_groups(drv, drv->groups);
if (ret)
bus_remove_driver(drv);
return ret;
}

说明：

1) driver_register()完成挂接驱动至总线及生成设备树的过程。

2) 首先调用driver_find()函数在spi总线上查找该驱动是否已经存在，如果存在，忙退出。

3) 如果该驱动在SPI总线上不存在，调用bus_add_driver(drv)增加该驱动。

4) 调用driver_add_groups(drv, drv->groups)函数增加驱动组。

接下来看bus_add_driver函数，程序如下：

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int bus_add_driver(struct device_driver *drv)
{
struct bus_type *bus;
struct driver_private *priv;
int error = 0;
bus = bus_get(drv->bus);
if (!bus)
return -EINVAL;
pr_debug("bus: '%s': add driver %s\n", bus->name, drv->name);
priv = kzalloc(sizeof(*priv), GFP_KERNEL);
if (!priv) {
error = -ENOMEM;
goto out_put_bus;
}
klist_init(&priv->klist_devices, NULL, NULL);
priv->driver = drv;
drv->p = priv;
priv->kobj.kset = bus->p->drivers_kset;
error = kobject_init_and_add(&priv->kobj, &driver_ktype, NULL,
"%s", drv->name);
if (error)
goto out_unregister;
if (drv->bus->p->drivers_autoprobe) {
error = driver_attach(drv); //这个函数是重点.
if (error)
goto out_unregister;
}
klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
module_add_driver(drv->owner, drv);
error = driver_create_file(drv, &driver_attr_uevent);
if (error) {
printk(KERN_ERR "%s: uevent attr (%s) failed\n",
__func__, drv->name);
}
error = driver_add_attrs(bus, drv);
if (error) {
/* How the hell do we get out of this pickle? Give up */
printk(KERN_ERR "%s: driver_add_attrs(%s) failed\n",
__func__, drv->name);
}
if (!drv->suppress_bind_attrs) {
error = add_bind_files(drv);
if (error) {
/* Ditto */
printk(KERN_ERR "%s: add_bind_files(%s) failed\n",
__func__, drv->name);
}
}
kobject_uevent(&priv->kobj, KOBJ_ADD);
return 0;
out_unregister:
kobject_put(&priv->kobj);
kfree(drv->p);
drv->p = NULL;
out_put_bus:
bus_put(bus);
return error;
}

说明：

1) 首先创建struct driver_private *priv结构体内存，注意此结构体是struct device_driver的成员变量。

2) 初始化priv成员变量。

3) 如果驱动总线支持自动探测，则调用error = driver_attach(drv); 实现探测。由(二)中bus_register()函数可以看出，bus->p->drivers_autoprobe = 1，支持自动探测。

4) driver_attach(drv); 的作用是：如果驱动还未挂接在总线上，挂接它并且调用probe函数进行探测。

点击(此处)折叠或打开

int driver_attach(struct device_driver *drv)
{
return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
}

这个函数会调用__driver_attach函数，如下：

点击(此处)折叠或打开

static int __driver_attach(struct device *dev, void *data)
{
struct device_driver *drv = data;
/*
* Lock device and try to bind to it. We drop the error
* here and always return 0, because we need to keep trying
* to bind to devices and some drivers will return an error
* simply if it didn't support the device.
*
* driver_probe_device() will spit a warning if there
* is an error.
*/
if (!driver_match_device(drv, dev))
return 0;
if (dev->parent) /* Needed for USB */
device_lock(dev->parent);
device_lock(dev);
if (!dev->driver)
driver_probe_device(drv, dev); //此函数就是我们要找的函数
device_unlock(dev);
if (dev->parent)
device_unlock(dev->parent);
return 0;
}

driver_probe_device()函数如下：

点击(此处)折叠或打开

int driver_probe_device(struct device_driver *drv, struct device *dev)
{
int ret = 0;
if (!device_is_registered(dev))
return -ENODEV;
pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
drv->bus->name, __func__, dev_name(dev), drv->name);
pm_runtime_get_noresume(dev);
pm_runtime_barrier(dev);
ret = really_probe(dev, drv);
pm_runtime_put_sync(dev);
return ret;
}

driver_probe_device函数中有一个really_probe函数,这是我们的最终目的地。

点击(此处)折叠或打开

static int really_probe(struct device *dev, struct device_driver *drv)
{
int ret = 0;
atomic_inc(&probe_count);
pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
drv->bus->name, __func__, drv->name, dev_name(dev));
WARN_ON(!list_empty(&dev->devres_head));
dev->driver = drv;
if (driver_sysfs_add(dev)) {
printk(KERN_ERR "%s: driver_sysfs_add(%s) failed\n",
__func__, dev_name(dev));
goto probe_failed;
}
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;
}
driver_bound(dev);
ret = 1;
pr_debug("bus: '%s': %s: bound device %s to driver %s\n",
drv->bus->name, __func__, dev_name(dev), drv->name);
goto done;
probe_failed:
devres_release_all(dev);
driver_sysfs_remove(dev);
dev->driver = NULL;
if (ret != -ENODEV && ret != -ENXIO) {
/* driver matched but the probe failed */
printk(KERN_WARNING
"%s: probe of %s failed with error %d\n",
drv->name, dev_name(dev), ret);
}
/*
* Ignore errors returned by ->probe so that the next driver can try
* its luck.
*/
ret = 0;
done:
atomic_dec(&probe_count);
wake_up(&probe_waitqueue);
return ret;
}

说明：

1) 在if (dev->bus->probe)中，由于此处还没有定义设备，所以不执行if里面的程序。在else if(drv->probe)中，驱动里面有探测函数，所以执行ret = drv->probe(dev);。因为此处还没有定义设备，所以此处执行没有效果。

在 bus_for_each_dev函数中可以找到device结构：

点击(此处)折叠或打开

int bus_for_each_dev(struct bus_type *bus, struct device *start,
void *data, int (*fn)(struct device *, void *))
{
struct klist_iter i;
struct device *dev;
int error = 0;
if (!bus)
return -EINVAL;
klist_iter_init_node(&bus->p->klist_devices, &i,
(start ? &start->p->knode_bus : NULL));
while ((dev = next_device(&i)) && !error)
error = fn(dev, data);
klist_iter_exit(&i);
return error;
}

说明：

1) 查找每个挂接在spi总线上的设备，看他们是否有注册，并调用相应的函数也就是__driver_attach函数。实际上就是查找device结构。

三、spi设备注册

在《Linux spi驱动分析(一)----总线驱动》中，spi_new_device()函数调用了spi_add_device(proxy)，程序如下：

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struct device {
struct device *parent;
struct device_private *p;
struct kobject kobj;
const char *init_name; /* initial name of the device */
const struct device_type *type;
struct mutex mutex; /* mutex 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 *platform_data; /* Platform specific data, device
core doesn't touch it */
struct dev_pm_info power;
struct dev_power_domain *pwr_domain;
#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;
struct device_node *of_node; /* associated device tree node */
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;
const struct attribute_group **groups; /* optional groups */
void (*release)(struct device *dev);
};
int spi_add_device(struct spi_device *spi)
{
static DEFINE_MUTEX(spi_add_lock);
struct device *dev = spi->master->dev.parent;
struct device *d;
int status;
/* Chipselects are numbered 0..max; validate. */
if (spi->chip_select >= spi->master->num_chipselect) {
dev_err(dev, "cs%d >= max %d\n",
spi->chip_select,
spi->master->num_chipselect);
return -EINVAL;
}
/* Set the bus ID string */
dev_set_name(&spi->dev, "%s.%u", dev_name(&spi->master->dev),
spi->chip_select);
/* We need to make sure there's no other device with this
* chipselect **BEFORE** we call setup(), else we'll trash
* its configuration. Lock against concurrent add() calls.
*/
mutex_lock(&spi_add_lock);
d = bus_find_device_by_name(&spi_bus_type, NULL, dev_name(&spi->dev));
if (d != NULL) {
dev_err(dev, "chipselect %d already in use\n",
spi->chip_select);
put_device(d);
status = -EBUSY;
goto done;
}
/* Drivers may modify this initial i/o setup, but will
* normally rely on the device being setup. Devices
* using SPI_CS_HIGH can't coexist well otherwise...
*/
status = spi_setup(spi);
if (status < 0) {
dev_err(dev, "can't setup %s, status %d\n",
dev_name(&spi->dev), status);
goto done;
}
/* Device may be bound to an active driver when this returns */
status = device_add(&spi->dev);
if (status < 0)
dev_err(dev, "can't add %s, status %d\n",
dev_name(&spi->dev), status);
else
dev_dbg(dev, "registered child %s\n", dev_name(&spi->dev));
done:
mutex_unlock(&spi_add_lock);
return status;
}

说明：

1) 在设备device的定义中，定义了这个设备挂接的总线和驱动。

2) spi_add_device()函数首先判断是否超出最大设备数，如果超过，直接退出。

3) 设置设备名称，此名称即是/sys/bus/spi/devices/下的一个目录。

4) 在spi总线上寻找此设备，如果找到，退出。

5) 调用spi_setup(spi)函数。

6) 调用device_add(&spi->dev)函数对设备进行初始化和注册。程序如下：

点击(此处)折叠或打开

int device_add(struct device *dev)
{
struct device *parent = NULL;
struct class_interface *class_intf;
int error = -EINVAL;
dev = get_device(dev);
if (!dev)
goto done;
if (!dev->p) {
error = device_private_init(dev);
if (error)
goto done;
}
/*
* for statically allocated devices, which should all be converted
* some day, we need to initialize the name. We prevent reading back
* the name, and force the use of dev_name()
*/
if (dev->init_name) {
dev_set_name(dev, "%s", dev->init_name);
dev->init_name = NULL;
}
if (!dev_name(dev)) {
error = -EINVAL;
goto name_error;
}
pr_debug("device: '%s': %s\n", dev_name(dev), __func__);
parent = get_device(dev->parent);
setup_parent(dev, parent);
/* use parent numa_node */
if (parent)
set_dev_node(dev, dev_to_node(parent));
/* first, register with generic layer. */
/* we require the name to be set before, and pass NULL */
error = kobject_add(&dev->kobj, dev->kobj.parent, NULL);
if (error)
goto Error;
/* notify platform of device entry */
if (platform_notify)
platform_notify(dev);
error = device_create_file(dev, &uevent_attr);
if (error)
goto attrError;
if (MAJOR(dev->devt)) {
error = device_create_file(dev, &devt_attr);
if (error)
goto ueventattrError;
error = device_create_sys_dev_entry(dev);
if (error)
goto devtattrError;
devtmpfs_create_node(dev);
}
error = device_add_class_symlinks(dev);
if (error)
goto SymlinkError;
error = device_add_attrs(dev);
if (error)
goto AttrsError;
error = bus_add_device(dev);
if (error)
goto BusError;
error = dpm_sysfs_add(dev);
if (error)
goto DPMError;
device_pm_add(dev);
/* Notify clients of device addition. This call must come
* after dpm_sysf_add() and before kobject_uevent().
*/
if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_ADD_DEVICE, dev);
kobject_uevent(&dev->kobj, KOBJ_ADD);
bus_probe_device(dev);
if (parent)
klist_add_tail(&dev->p->knode_parent,
&parent->p->klist_children);
if (dev->class) {
mutex_lock(&dev->class->p->class_mutex);
/* tie the class to the device */
klist_add_tail(&dev->knode_class,
&dev->class->p->klist_devices);
/* notify any interfaces that the device is here */
list_for_each_entry(class_intf,
&dev->class->p->class_interfaces, node)
if (class_intf->add_dev)
class_intf->add_dev(dev, class_intf);
mutex_unlock(&dev->class->p->class_mutex);
}
done:
put_device(dev);
return error;
DPMError:
bus_remove_device(dev);
BusError:
device_remove_attrs(dev);
AttrsError:
device_remove_class_symlinks(dev);
SymlinkError:
if (MAJOR(dev->devt))
devtmpfs_delete_node(dev);
if (MAJOR(dev->devt))
device_remove_sys_dev_entry(dev);
devtattrError:
if (MAJOR(dev->devt))
device_remove_file(dev, &devt_attr);
ueventattrError:
device_remove_file(dev, &uevent_attr);
attrError:
kobject_uevent(&dev->kobj, KOBJ_REMOVE);
kobject_del(&dev->kobj);
Error:
cleanup_device_parent(dev);
if (parent)
put_device(parent);
name_error:
kfree(dev->p);
dev->p = NULL;
goto done;
}

说明：

1) 首先获取设备dev，对dev的成员进行初始化。

2) kobject_add()完成目录的创建。

3) 创建文件。

4) bus_probe_device(dev);，总线探测设备，程序如下：

点击(此处)折叠或打开

void bus_probe_device(struct device *dev)
{
struct bus_type *bus = dev->bus;
int ret;
if (bus && bus->p->drivers_autoprobe) {
ret = device_attach(dev);
WARN_ON(ret < 0);
}
}
int device_attach(struct device *dev)
{
int ret = 0;
device_lock(dev);
if (dev->driver) {
if (klist_node_attached(&dev->p->knode_driver)) {
ret = 1;
goto out_unlock;
}
ret = device_bind_driver(dev);
if (ret == 0)
ret = 1;
else {
dev->driver = NULL;
ret = 0;
}
} else {
pm_runtime_get_noresume(dev);
ret = bus_for_each_drv(dev->bus, NULL, dev, __device_attach);
pm_runtime_put_sync(dev);
}
out_unlock:
device_unlock(dev);
return ret;
}

说明：
1) 由(二)中的总线注册函数可知，bus->p->drivers_autoprobe = 1。

2) 调用device_attach()函数加载设备。

3) 由于程序还没有对dev->driver进行赋值，所以此处程序走的是else。

4) bus_for_each_drv()函数调用__device_attach()函数，程序如下：

点击(此处)折叠或打开

int bus_for_each_drv(struct bus_type *bus, struct device_driver *start,
void *data, int (*fn)(struct device_driver *, void *))
{
struct klist_iter i;
struct device_driver *drv;
int error = 0;
if (!bus)
return -EINVAL;
klist_iter_init_node(&bus->p->klist_drivers, &i,
start ? &start->p->knode_bus : NULL);
while ((drv = next_driver(&i)) && !error)
error = fn(drv, data);
klist_iter_exit(&i);
return error;
}
static inline int driver_match_device(struct device_driver *drv,
struct device *dev)
{
return drv->bus->match ? drv->bus->match(dev, drv) : 1;
}
static int __device_attach(struct device_driver *drv, void *data)
{
struct device *dev = data;
if (!driver_match_device(drv, dev))
return 0;
return driver_probe_device(drv, dev);
}

说明：
1) __device_attach()函数使用了两个参数，一个参数为dev，另外一个就是bus_for_each_drv()函数提供的。

2) __device_attach()函数首先使用函数driver_match_device(drv, dev)查看驱动是否匹配设备，如果不匹配，退出。driver_match_device(drv, dev)中，判断是否有drv->bus->match，从(二)总线注册中知道，总线中有match，所以调用(二)中的spi_match_device()函数。

3) driver_probe_device()函数完成驱动探测，程序如下：

点击(此处)折叠或打开

int driver_probe_device(struct device_driver *drv, struct device *dev)
{
int ret = 0;
if (!device_is_registered(dev))
return -ENODEV;
pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
drv->bus->name, __func__, dev_name(dev), drv->name);
pm_runtime_get_noresume(dev);
pm_runtime_barrier(dev);
ret = really_probe(dev, drv);
pm_runtime_put_sync(dev);
return ret;
}
static int really_probe(struct device *dev, struct device_driver *drv)
{
int ret = 0;
atomic_inc(&probe_count);
pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
drv->bus->name, __func__, drv->name, dev_name(dev));
WARN_ON(!list_empty(&dev->devres_head));
dev->driver = drv;
if (driver_sysfs_add(dev)) {
printk(KERN_ERR "%s: driver_sysfs_add(%s) failed\n",
__func__, dev_name(dev));
goto probe_failed;
}
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;
}
driver_bound(dev);
ret = 1;
pr_debug("bus: '%s': %s: bound device %s to driver %s\n",
drv->bus->name, __func__, dev_name(dev), drv->name);
goto done;
probe_failed:
devres_release_all(dev);
driver_sysfs_remove(dev);
dev->driver = NULL;
if (ret != -ENODEV && ret != -ENXIO) {
/* driver matched but the probe failed */
printk(KERN_WARNING
"%s: probe of %s failed with error %d\n",
drv->name, dev_name(dev), ret);
}
/*
* Ignore errors returned by ->probe so that the next driver can try
* its luck.
*/
ret = 0;
done:
atomic_dec(&probe_count);
wake_up(&probe_waitqueue);
return ret;
}

说明：

1) driver_probe_device()函数调用really_probe()函数。

2) 在really_probe()函数中，由于设备的总线中没有探测函数，所以不执行if (dev->bus->probe)。

3) spi驱动中有探测函数，所以执行else if (drv->probe)里面的程序，即ret = drv->probe(dev);，从(三)中的int spi_register_driver(struct spi_driver *sdrv)函数可以看到，驱动的探测函数为spi_drv_probe()，程序如下：

点击(此处)折叠或打开

static int spi_drv_probe(struct device *dev)
{
const struct spi_driver *sdrv = to_spi_driver(dev->driver);
return sdrv->probe(to_spi_device(dev));
}

说明：

1) 首先获取spi_driver结构体。

2) 调用spi_driver结构体中的探测函数，即为(三)中的w25q_probe()函数。
在really_probe()函数中，调用driver_bound(dev);函数实现设备与驱动的绑定，程序如下：

点击(此处)折叠或打开

static void driver_bound(struct device *dev)
{
if (klist_node_attached(&dev->p->knode_driver)) {
printk(KERN_WARNING "%s: device %s already bound\n",
__func__, kobject_name(&dev->kobj));
return;
}
pr_debug("driver: '%s': %s: bound to device '%s'\n", dev_name(dev),
__func__, dev->driver->name);
klist_add_tail(&dev->p->knode_driver, &dev->driver->p->klist_devices);
if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_BOUND_DRIVER, dev);
}

说明：

1) 使用klist_add_tail()将设备与驱动链接在一起。

四、总结

在device和device_drive结构中，device中存在一个struct device_driver *driver，而在device_drive中并没有同样的包含device结构。对于一个设备来说，只能绑定一个驱动；而对于一个驱动来说，可以对应多个设备。也就是说这里device中的driver指针将会指向其绑定的驱动。回到probe探测函数，对一个设备驱动进行注册的过程中，会在其相应的总线（也就是其挂接的总线）上发出一个探测，这个探测会搜寻所有挂接在这个总线上的尚未被绑定的设备（也就是driver指针为NULL），然后将driver指针指向这个驱动的结构，同时将这个设备的device结构挂接在device_driver结构中的klist链表中。当一个设备被注册时，它也会去寻找挂接在同一条总线上的驱动，并将自己与这个驱动联系起来。

五、spi传输函数

spi核心提供了数据传输函数，如下：

点击(此处)折叠或打开

static inline void spi_message_init(struct spi_message *m)
{
memset(m, 0, sizeof *m);
INIT_LIST_HEAD(&m->transfers);
}
static inline void
spi_message_add_tail(struct spi_transfer *t, struct spi_message *m)
{
list_add_tail(&t->transfer_list, &m->transfers);
}
static inline int
spi_write(struct spi_device *spi, const void *buf, size_t len)
{
struct spi_transfer t = {
.tx_buf = buf,
.len = len,
};
struct spi_message m;
spi_message_init(&m);
spi_message_add_tail(&t, &m);
return spi_sync(spi, &m);
}
static inline int
spi_read(struct spi_device *spi, void *buf, size_t len)
{
struct spi_transfer t = {
.rx_buf = buf,
.len = len,
};
struct spi_message m;
spi_message_init(&m);
spi_message_add_tail(&t, &m);
return spi_sync(spi, &m);
}
static inline ssize_t spi_w8r8(struct spi_device *spi, u8 cmd)
{
ssize_t status;
u8 result;
status = spi_write_then_read(spi, &cmd, 1, &result, 1);
/* return negative errno or unsigned value */
return (status < 0) ? status : result;
}
static inline ssize_t spi_w8r16(struct spi_device *spi, u8 cmd)
{
ssize_t status;
u16 result;
status = spi_write_then_read(spi, &cmd, 1, (u8 *) &result, 2);
/* return negative errno or unsigned value */
return (status < 0) ? status : result;
}

说明：

1) 传输开始时，首先初始化spi_message，然后将传输的spi_transfer链入spi_message中。
2) spi_message中，有一个transfers队列，spi_transfer结构体通过这个队列挂到spi_message中。一个spi_message代表一次传输会话，spi_transfer代表一次单独的IO操作。比如，有些spi设备需要先读后写，那么这个读写过程就是一次spi会话，里面包括两个transfer，一个定义写操作的参数，另一个定义读操作的参数。

3) 最后都是调用spi_sync()函数实现传输的，如下：

点击(此处)折叠或打开

int spi_sync(struct spi_device *spi, struct spi_message *message)
{
return __spi_sync(spi, message, 0);
}
static int __spi_sync(struct spi_device *spi, struct spi_message *message,
int bus_locked)
{
DECLARE_COMPLETION_ONSTACK(done);
int status;
struct spi_master *master = spi->master;
message->complete = spi_complete;
message->context = &done;
if (!bus_locked)
mutex_lock(&master->bus_lock_mutex);
status = spi_async_locked(spi, message);
if (!bus_locked)
mutex_unlock(&master->bus_lock_mutex);
if (status == 0) {
wait_for_completion(&done);
status = message->status;
}
message->context = NULL;
return status;
}
int spi_async_locked(struct spi_device *spi, struct spi_message *message)
{
struct spi_master *master = spi->master;
int ret;
unsigned long flags;
spin_lock_irqsave(&master->bus_lock_spinlock, flags);
ret = __spi_async(spi, message);
spin_unlock_irqrestore(&master->bus_lock_spinlock, flags);
return ret;
}
static int __spi_async(struct spi_device *spi, struct spi_message *message)
{
struct spi_master *master = spi->master;
/* Half-duplex links include original MicroWire, and ones with
* only one data pin like SPI_3WIRE (switches direction) or where
* either MOSI or MISO is missing. They can also be caused by
* software limitations.
*/
if ((master->flags & SPI_MASTER_HALF_DUPLEX)
|| (spi->mode & SPI_3WIRE)) {
struct spi_transfer *xfer;
unsigned flags = master->flags;
list_for_each_entry(xfer, &message->transfers, transfer_list) {
if (xfer->rx_buf && xfer->tx_buf)
return -EINVAL;
if ((flags & SPI_MASTER_NO_TX) && xfer->tx_buf)
return -EINVAL;
if ((flags & SPI_MASTER_NO_RX) && xfer->rx_buf)
return -EINVAL;
}
}
message->spi = spi;
message->status = -EINPROGRESS;
return master->transfer(spi, message);
}

说明：

1) 由上面的函数调用轨迹看，最后就是调用master的transfer函数实现传输的。

drv

Linux spi驱动分析(二)----SPI核心(bus、device_driver和device)

二、spi驱动注册

三、spi设备注册

四、总结

五、spi传输函数