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

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。

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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/sys/bus/spi。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：

点击(此处)折叠或打开

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。

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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：

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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：

点击(此处)折叠或打开

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。

from：http://blog.chinaunix.net/uid-25445243-id-4032371.html