linux驱动之I2C

include/linux/i2c.h

struct i2c_msg;
struct i2c_algorithm;
struct i2c_adapter;
struct i2c_client;
struct i2c_driver;
union i2c_smbus_data;

I2C驱动主要包含三部分：I2C核心、I2C总线驱动、I2C设备驱动，它们主要的数据结构在目录：/include/linux/i2c.h

　　struct i2c_driver

 1 /*
 2  * A driver is capable of handling one or more physical devices present on
 3  * I2C adapters. This information is used to inform the driver of adapter
 4  * events.
 5  *
 6  * The driver.owner field should be set to the module owner of this driver.
 7  * The driver.name field should be set to the name of this driver.
 8  */
 9 struct i2c_driver {
10     int id;
11     unsigned int class;
12 
13     /* Notifies the driver that a new bus has appeared. This routine
14      * can be used by the driver to test if the bus meets its conditions
15      * & seek for the presence of the chip(s) it supports. If found, it
16      * registers the client(s) that are on the bus to the i2c admin. via
17      * i2c_attach_client.  (LEGACY I2C DRIVERS ONLY)
18      */
19     int (*attach_adapter)(struct i2c_adapter *);
20     int (*detach_adapter)(struct i2c_adapter *);
21 
22     /* tells the driver that a client is about to be deleted & gives it
23      * the chance to remove its private data. Also, if the client struct
24      * has been dynamically allocated by the driver in the function above,
25      * it must be freed here.  (LEGACY I2C DRIVERS ONLY)
26      */
27     int (*detach_client)(struct i2c_client *);
28 
29     /* Standard driver model interfaces, for "new style" i2c drivers.
30      * With the driver model, device enumeration is NEVER done by drivers;
31      * it's done by infrastructure.  (NEW STYLE DRIVERS ONLY)
32      */
33     int (*probe)(struct i2c_client *);
34     int (*remove)(struct i2c_client *);
35 
36     /* driver model interfaces that don't relate to enumeration  */
37     void (*shutdown)(struct i2c_client *);
38     int (*suspend)(struct i2c_client *, pm_message_t mesg);
39     int (*resume)(struct i2c_client *);
40 
41     /* a ioctl like command that can be used to perform specific functions
42      * with the device.
43      */
44     int (*command)(struct i2c_client *client,unsigned int cmd, void *arg);
45 
46     struct device_driver driver;
47     struct list_head list;
48 };

　　struct i2c_client

 1 /**
 2  * struct i2c_client - represent an I2C slave device
 3  * @addr: Address used on the I2C bus connected to the parent adapter.
 4  * @name: Indicates the type of the device, usually a chip name that's
 5  *    generic enough to hide second-sourcing and compatible revisions.
 6  * @dev: Driver model device node for the slave.
 7  * @driver_name: Identifies new-style driver used with this device; also
 8  *    used as the module name for hotplug/coldplug modprobe support.
 9  *
10  * An i2c_client identifies a single device (i.e. chip) connected to an
11  * i2c bus. The behaviour is defined by the routines of the driver.
12  */
13 struct i2c_client {
14     unsigned short flags;        /* div., see below        */
15     unsigned short addr;        /* chip address - NOTE: 7bit    */
16                     /* addresses are stored in the    */
17                     /* _LOWER_ 7 bits        */
18     char name[I2C_NAME_SIZE];
19     struct i2c_adapter *adapter;    /* the adapter we sit on    */
20     struct i2c_driver *driver;    /* and our access routines    */
21     int usage_count;        /* How many accesses currently  */
22                     /* to the client        */
23     struct device dev;        /* the device structure        */
24     int irq;            /* irq issued by device (or -1) */
25     char driver_name[KOBJ_NAME_LEN];
26     struct list_head list;
27     struct completion released;
28 };

　　struct i2c_algorithm

 1 /*
 2  * The following structs are for those who like to implement new bus drivers:
 3  * i2c_algorithm is the interface to a class of hardware solutions which can
 4  * be addressed using the same bus algorithms - i.e. bit-banging or the PCF8584
 5  * to name two of the most common.
 6  */
 7 struct i2c_algorithm {
 8     /* If an adapter algorithm can't do I2C-level access, set master_xfer
 9        to NULL. If an adapter algorithm can do SMBus access, set
10        smbus_xfer. If set to NULL, the SMBus protocol is simulated
11        using common I2C messages */
12     /* master_xfer should return the number of messages successfully
13        processed, or a negative value on error */
14     int (*master_xfer)(struct i2c_adapter *adap,struct i2c_msg *msgs,
15                        int num);
16     int (*smbus_xfer) (struct i2c_adapter *adap, u16 addr,
17                        unsigned short flags, char read_write,
18                        u8 command, int size, union i2c_smbus_data * data);
19 
20     /* --- ioctl like call to set div. parameters. */
21     int (*algo_control)(struct i2c_adapter *, unsigned int, unsigned long);
22 
23     /* To determine what the adapter supports */
24     u32 (*functionality) (struct i2c_adapter *);
25 };

　　struct i2c_adapter

 1 /*
 2  * i2c_adapter is the structure used to identify a physical i2c bus along
 3  * with the access algorithms necessary to access it.
 4  */
 5 struct i2c_adapter {
 6     struct module *owner;
 7     unsigned int id;
 8     unsigned int class;
 9     const struct i2c_algorithm *algo; /* the algorithm to access the bus */
10     void *algo_data;
11 
12     /* --- administration stuff. */
13     int (*client_register)(struct i2c_client *);
14     int (*client_unregister)(struct i2c_client *);
15 
16     /* data fields that are valid for all devices    */
17     u8 level;             /* nesting level for lockdep */
18     struct mutex bus_lock;
19     struct mutex clist_lock;
20 
21     int timeout;
22     int retries;
23     struct device dev;        /* the adapter device */
24 
25     int nr;
26     struct list_head clients;
27     struct list_head list;
28     char name[48];
29     struct completion dev_released;
30 }

I2C核心

　　I2C核心提供了I2C总线驱动和设备驱动的注册、注销方法，I2C通信方法(algorithm)上层的与具体适配器无关的代码以及探测设备、检测设备地址的上层代码等。

I2C总线驱动

　　I2C总线驱动是对I2C硬件体系结构中适配器段端的实现，适配器可由CPU控制，甚至可以直接集成在CPU内部。I2C总线驱动主要包括I2C适配器数据结构i2c_adapter、I2C适配器的Algorithm数据结构i2c_algorithm和控制I2C适配器产生通信信号的函数。经由I2C总线驱动的代码，我们可以控制I2C适配器以主控方式产生开始位、停止位、读写周期，以及从设备方式读写、产生ACK等。

I2C设备驱动

I2C设备驱动即客户驱动时对I2C硬件体系结构中设备端的实现，设备一般挂接在受CPU控制的I2C适配器上，通过I2C适配器与CPU交换数据。I2C设备驱动主要包含数据结构i2c_driver和i2c_client，我们需要具体设备实现其中的成员函数。

　　在linux2.6内核中，所有设备都在sysfs文件系统中显示，在sysfs虚拟文件系统中存放了驱动挂载的总线以及device、driver，当我们注册一个driver后，内核会将我们注册的这个driver添加到这类驱动总线上这类总线的拥有一个共同的类似于一个基类kobject，而kset就是koject的一个集合。我们在写驱动的时候一般不会去分析kobject、kset，毕竟他们在内核里面是非常顶层的软件抽象层，但是对于内核整个驱动框架，却不能不分析这类抽象层，下图是我在树莓派所做的截图：

　　我们可以看到在sys文件目录下面有bus、class等，进入bus后会看到各种设备驱动，如在I2C中我们可以看到device、drivers,当然这些目录下面都没有什么内容应为sysfs是一个虚拟文件系统主要是记录各个进程和内核方面的信息。我们的驱动设备如何和虚拟文件系统产生关系了呢，就是kobject在这儿起了作用，我们的device、driver最终都会挂载一个总线上，后面我们会看到sysfs申请内存为device或者driver建立节点。

　　同样注册一个device后也会挂载在总线上。其实I2C我们也可以看成设备-总线-驱动模型，

　　i2c_register_driver(THIS_MODULE, driver)

 1 /*
 2  * An i2c_driver is used with one or more i2c_client (device) nodes to access
 3  * i2c slave chips, on a bus instance associated with some i2c_adapter.  There
 4  * are two models for binding the driver to its device:  "new style" drivers
 5  * follow the standard Linux driver model and just respond to probe() calls
 6  * issued if the driver core sees they match(); "legacy" drivers create device
 7  * nodes themselves.
 8  */
 9 
10 int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
11 {
12     int res;
13 
14     /* new style driver methods can't mix with legacy ones */
15     if (is_newstyle_driver(driver)) {
16         if (driver->attach_adapter || driver->detach_adapter
17                 || driver->detach_client) {
18             printk(KERN_WARNING
19                     "i2c-core: driver [%s] is confused\n",
20                     driver->driver.name);
21             return -EINVAL;
22         }
23     }
24 
25     /* add the driver to the list of i2c drivers in the driver core */
26     driver->driver.owner = owner;
27     driver->driver.bus = &i2c_bus_type;
28 
29     /* for new style drivers, when registration returns the driver core
30      * will have called probe() for all matching-but-unbound devices.
31      */
32     res = driver_register(&driver->driver);
33     if (res)
34         return res;
35 
36     mutex_lock(&core_lists);
37 
38     list_add_tail(&driver->list,&drivers);
39     pr_debug("i2c-core: driver [%s] registered\n", driver->driver.name);
40 
41     /* legacy drivers scan i2c busses directly */
42     if (driver->attach_adapter) {
43         struct i2c_adapter *adapter;
44 
45         list_for_each_entry(adapter, &adapters, list) {
46             driver->attach_adapter(adapter);
47         }
48     }
49 
50     mutex_unlock(&core_lists);
51     return 0;
52 }

　　driver_register(&driver->driver);

 1 /**
 2  *    driver_register - register driver with bus
 3  *    @drv:    driver to register
 4  *
 5  *    We pass off most of the work to the bus_add_driver() call,
 6  *    since most of the things we have to do deal with the bus
 7  *    structures.
 8  */
 9 int driver_register(struct device_driver * drv)
10 {
11     if ((drv->bus->probe && drv->probe) ||
12         (drv->bus->remove && drv->remove) ||
13         (drv->bus->shutdown && drv->shutdown)) {
14         printk(KERN_WARNING "Driver '%s' needs updating - please use bus_type methods\n", drv->name);
15     }
16     klist_init(&drv->klist_devices, NULL, NULL);
17     return bus_add_driver(drv);
18 }

　　klist_init(&drv->klist_devices, NULL, NULL);

 1 /**
 2  *    driver_register - register driver with bus
 3  *    @drv:    driver to register
 4  *
 5  *    We pass off most of the work to the bus_add_driver() call,
 6  *    since most of the things we have to do deal with the bus
 7  *    structures.
 8  */
 9 int driver_register(struct device_driver * drv)
10 {
11     if ((drv->bus->probe && drv->probe) ||
12         (drv->bus->remove && drv->remove) ||
13         (drv->bus->shutdown && drv->shutdown)) {
14         printk(KERN_WARNING "Driver '%s' needs updating - please use bus_type methods\n", drv->name);
15     }
16     klist_init(&drv->klist_devices, NULL, NULL);
17     return bus_add_driver(drv);
18 }

　　bus_add_driver(drv);

 1 /**
 2  *    bus_add_driver - Add a driver to the bus.
 3  *    @drv:    driver.
 4  *
 5  */
 6 int bus_add_driver(struct device_driver *drv)
 7 {
 8     struct bus_type * bus = get_bus(drv->bus);
 9     int error = 0;
10 
11     if (!bus)
12         return -EINVAL;
13 
14     pr_debug("bus %s: add driver %s\n", bus->name, drv->name);
15     error = kobject_set_name(&drv->kobj, "%s", drv->name);
16     if (error)
17         goto out_put_bus;
18     drv->kobj.kset = &bus->drivers;
19     if ((error = kobject_register(&drv->kobj)))
20         goto out_put_bus;
21 
22     if (drv->bus->drivers_autoprobe) {
23         error = driver_attach(drv);
24         if (error)
25             goto out_unregister;
26     }
27     klist_add_tail(&drv->knode_bus, &bus->klist_drivers);
28     module_add_driver(drv->owner, drv);
29 
30     error = driver_add_attrs(bus, drv);
31     if (error) {
32         /* How the hell do we get out of this pickle? Give up */
33         printk(KERN_ERR "%s: driver_add_attrs(%s) failed\n",
34             __FUNCTION__, drv->name);
35     }
36     error = add_bind_files(drv);
37     if (error) {
38         /* Ditto */
39         printk(KERN_ERR "%s: add_bind_files(%s) failed\n",
40             __FUNCTION__, drv->name);
41     }
42 
43     return error;
44 out_unregister:
45     kobject_unregister(&drv->kobj);
46 out_put_bus:
47     put_bus(bus);
48     return error;
49 }

　　kobject_register(&drv->kobj)

 1 /**
 2  *    kobject_register - initialize and add an object.
 3  *    @kobj:    object in question.
 4  */
 5 
 6 int kobject_register(struct kobject * kobj)
 7 {
 8     int error = -EINVAL;
 9     if (kobj) {
10         kobject_init(kobj);
11         error = kobject_add(kobj);
12         if (!error)
13             kobject_uevent(kobj, KOBJ_ADD);
14     }
15     return error;
16 }

 kobject_add(kobj);

1 /**
2  *    kobject_add - add an object to the hierarchy.
3  *    @kobj:    object.
4  */
5 int kobject_add(struct kobject * kobj)
6 {
7     return kobject_shadow_add(kobj, NULL);
8 }

　　kobject_shadow_add(kobj, NULL);

 1 /**
 2  *    kobject_shadow_add - add an object to the hierarchy.
 3  *    @kobj:    object.
 4  *    @shadow_parent: sysfs directory to add to.
 5  */
 6 
 7 int kobject_shadow_add(struct kobject * kobj, struct dentry *shadow_parent)
 8 {
 9     int error = 0;
10     struct kobject * parent;
11 
12     if (!(kobj = kobject_get(kobj)))
13         return -ENOENT;
14     if (!kobj->k_name)
15         kobj->k_name = kobj->name;
16     if (!*kobj->k_name) {
17         pr_debug("kobject attempted to be registered with no name!\n");
18         WARN_ON(1);
19         kobject_put(kobj);
20         return -EINVAL;
21     }
22     parent = kobject_get(kobj->parent);
23 
24     pr_debug("kobject %s: registering. parent: %s, set: %s\n",
25          kobject_name(kobj), parent ? kobject_name(parent) : "<NULL>", 
26          kobj->kset ? kobj->kset->kobj.name : "<NULL>" );
27 
28     if (kobj->kset) {
29         spin_lock(&kobj->kset->list_lock);
30 
31         if (!parent)
32             parent = kobject_get(&kobj->kset->kobj);
33 
34         list_add_tail(&kobj->entry,&kobj->kset->list);
35         spin_unlock(&kobj->kset->list_lock);
36         kobj->parent = parent;
37     }
38 
39     error = create_dir(kobj, shadow_parent);
40     if (error) {
41         /* unlink does the kobject_put() for us */
42         unlink(kobj);
43         kobject_put(parent);
44 
45         /* be noisy on error issues */
46         if (error == -EEXIST)
47             printk(KERN_ERR "kobject_add failed for %s with "
48                    "-EEXIST, don't try to register things with "
49                    "the same name in the same directory.\n",
50                    kobject_name(kobj));
51         else
52             printk(KERN_ERR "kobject_add failed for %s (%d)\n",
53                    kobject_name(kobj), error);
54         dump_stack();
55     }
56 
57     return error;
58 }

　　create_dir(kobj, shadow_parent);　

 1 static int create_dir(struct kobject * kobj, struct dentry *shadow_parent)
 2 {
 3     int error = 0;
 4     if (kobject_name(kobj)) {
 5         error = sysfs_create_dir(kobj, shadow_parent);
 6         if (!error) {
 7             if ((error = populate_dir(kobj)))
 8                 sysfs_remove_dir(kobj);
 9         }
10     }
11     return error;
12 }

　　sysfs_create_dir(kobj, shadow_parent);

 1 /**
 2  *    sysfs_create_dir - create a directory for an object.
 3  *    @kobj:        object we're creating directory for. 
 4  *    @shadow_parent:    parent parent object.
 5  */
 6 
 7 int sysfs_create_dir(struct kobject * kobj, struct dentry *shadow_parent)
 8 {
 9     struct dentry * dentry = NULL;
10     struct dentry * parent;
11     int error = 0;
12 
13     BUG_ON(!kobj);
14 
15     if (shadow_parent)
16         parent = shadow_parent;
17     else if (kobj->parent)
18         parent = kobj->parent->dentry;
19     else if (sysfs_mount && sysfs_mount->mnt_sb)
20         parent = sysfs_mount->mnt_sb->s_root;
21     else
22         return -EFAULT;
23 
24     error = create_dir(kobj,parent,kobject_name(kobj),&dentry);
25     if (!error)
26         kobj->dentry = dentry;
27     return error;
28 }

　　create_dir(kobj,parent,kobject_name(kobj),&dentry);

 1 static int create_dir(struct kobject * k, struct dentry * p,
 2               const char * n, struct dentry ** d)
 3 {
 4     int error;
 5     umode_t mode = S_IFDIR| S_IRWXU | S_IRUGO | S_IXUGO;
 6 
 7     mutex_lock(&p->d_inode->i_mutex);
 8     *d = lookup_one_len(n, p, strlen(n));
 9     if (!IS_ERR(*d)) {
10          if (sysfs_dirent_exist(p->d_fsdata, n))
11               error = -EEXIST;
12           else
13             error = sysfs_make_dirent(p->d_fsdata, *d, k, mode,
14                                 SYSFS_DIR);
15         if (!error) {
16             error = sysfs_create(*d, mode, init_dir);
17             if (!error) {
18                 inc_nlink(p->d_inode);
19                 (*d)->d_op = &sysfs_dentry_ops;
20                 d_rehash(*d);
21             }
22         }
23         if (error && (error != -EEXIST)) {
24             struct sysfs_dirent *sd = (*d)->d_fsdata;
25             if (sd) {
26                  list_del_init(&sd->s_sibling);
27                 sysfs_put(sd);
28             }
29             d_drop(*d);
30         }
31         dput(*d);
32     } else
33         error = PTR_ERR(*d);
34     mutex_unlock(&p->d_inode->i_mutex);
35     return error;
36 }

　　
　　sysfs_create(*d, mode, init_dir);

 1 int sysfs_create(struct dentry * dentry, int mode, int (*init)(struct inode *))
 2 {
 3     int error = 0;
 4     struct inode * inode = NULL;
 5     if (dentry) {
 6         if (!dentry->d_inode) {
 7             struct sysfs_dirent * sd = dentry->d_fsdata;
 8             if ((inode = sysfs_new_inode(mode, sd))) {
 9                 if (dentry->d_parent && dentry->d_parent->d_inode) {
10                     struct inode *p_inode = dentry->d_parent->d_inode;
11                     p_inode->i_mtime = p_inode->i_ctime = CURRENT_TIME;
12                 }
13                 goto Proceed;
14             }
15             else 
16                 error = -ENOMEM;
17         } else
18             error = -EEXIST;
19     } else 
20         error = -ENOENT;
21     goto Done;
22 
23  Proceed:
24     if (init)
25         error = init(inode);
26     if (!error) {
27         d_instantiate(dentry, inode);
28         if (S_ISDIR(mode))
29             dget(dentry);  /* pin only directory dentry in core */
30     } else
31         iput(inode);
32  Done:
33     return error;
34 }

　　sysfs_create(*d, mode, init_dir);

 1 int sysfs_create(struct dentry * dentry, int mode, int (*init)(struct inode *))
 2 {
 3     int error = 0;
 4     struct inode * inode = NULL;
 5     if (dentry) {
 6         if (!dentry->d_inode) {
 7             struct sysfs_dirent * sd = dentry->d_fsdata;
 8             if ((inode = sysfs_new_inode(mode, sd))) {
 9                 if (dentry->d_parent && dentry->d_parent->d_inode) {
10                     struct inode *p_inode = dentry->d_parent->d_inode;
11                     p_inode->i_mtime = p_inode->i_ctime = CURRENT_TIME;
12                 }
13                 goto Proceed;
14             }
15             else 
16                 error = -ENOMEM;
17         } else
18             error = -EEXIST;
19     } else 
20         error = -ENOENT;
21     goto Done;
22 
23  Proceed:
24     if (init)
25         error = init(inode);
26     if (!error) {
27         d_instantiate(dentry, inode);
28         if (S_ISDIR(mode))
29             dget(dentry);  /* pin only directory dentry in core */
30     } else
31         iput(inode);
32  Done:
33     return error;
34 }

　　sysfs_new_inode(mode, sd))

 1 struct inode * sysfs_new_inode(mode_t mode, struct sysfs_dirent * sd)
 2 {
 3     struct inode * inode = new_inode(sysfs_sb);
 4     if (inode) {
 5         inode->i_blocks = 0;
 6         inode->i_mapping->a_ops = &sysfs_aops;
 7         inode->i_mapping->backing_dev_info = &sysfs_backing_dev_info;
 8         inode->i_op = &sysfs_inode_operations;
 9         inode->i_ino = sd->s_ino;
10         lockdep_set_class(&inode->i_mutex, &sysfs_inode_imutex_key);
11 
12         if (sd->s_iattr) {
13             /* sysfs_dirent has non-default attributes
14              * get them for the new inode from persistent copy
15              * in sysfs_dirent
16              */
17             set_inode_attr(inode, sd->s_iattr);
18         } else
19             set_default_inode_attr(inode, mode);
20     }
21     return inode;
22 }

　　new_inode(sysfs_sb);

 1 /**
 2  *    new_inode     - obtain an inode
 3  *    @sb: superblock
 4  *
 5  *    Allocates a new inode for given superblock.
 6  */
 7 struct inode *new_inode(struct super_block *sb)
 8 {
 9     /*
10      * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW
11      * error if st_ino won't fit in target struct field. Use 32bit counter
12      * here to attempt to avoid that.
13      */
14     static unsigned int last_ino;
15     struct inode * inode;
16 
17     spin_lock_prefetch(&inode_lock);
18     
19     inode = alloc_inode(sb);
20     if (inode) {
21         spin_lock(&inode_lock);
22         inodes_stat.nr_inodes++;
23         list_add(&inode->i_list, &inode_in_use);
24         list_add(&inode->i_sb_list, &sb->s_inodes);
25         inode->i_ino = ++last_ino;
26         inode->i_state = 0;
27         spin_unlock(&inode_lock);
28     }
29     return inode;
30 }

　　alloc_inode(sb);

 1 static struct inode *alloc_inode(struct super_block *sb)
 2 {
 3     static const struct address_space_operations empty_aops;
 4     static struct inode_operations empty_iops;
 5     static const struct file_operations empty_fops;
 6     struct inode *inode;
 7 
 8     if (sb->s_op->alloc_inode)
 9         inode = sb->s_op->alloc_inode(sb);
10     else
11         inode = (struct inode *) kmem_cache_alloc(inode_cachep, GFP_KERNEL);
12 
13     if (inode) {
14         struct address_space * const mapping = &inode->i_data;
15 
16         inode->i_sb = sb;
17         inode->i_blkbits = sb->s_blocksize_bits;
18         inode->i_flags = 0;
19         atomic_set(&inode->i_count, 1);
20         inode->i_op = &empty_iops;
21         inode->i_fop = &empty_fops;
22         inode->i_nlink = 1;
23         atomic_set(&inode->i_writecount, 0);
24         inode->i_size = 0;
25         inode->i_blocks = 0;
26         inode->i_bytes = 0;
27         inode->i_generation = 0;
28 #ifdef CONFIG_QUOTA
29         memset(&inode->i_dquot, 0, sizeof(inode->i_dquot));
30 #endif
31         inode->i_pipe = NULL;
32         inode->i_bdev = NULL;
33         inode->i_cdev = NULL;
34         inode->i_rdev = 0;
35         inode->dirtied_when = 0;
36         if (security_inode_alloc(inode)) {
37             if (inode->i_sb->s_op->destroy_inode)
38                 inode->i_sb->s_op->destroy_inode(inode);
39             else
40                 kmem_cache_free(inode_cachep, (inode));
41             return NULL;
42         }
43 
44         mapping->a_ops = &empty_aops;
45          mapping->host = inode;
46         mapping->flags = 0;
47         mapping_set_gfp_mask(mapping, GFP_HIGHUSER);
48         mapping->assoc_mapping = NULL;
49         mapping->backing_dev_info = &default_backing_dev_info;
50 
51         /*
52          * If the block_device provides a backing_dev_info for client
53          * inodes then use that.  Otherwise the inode share the bdev's
54          * backing_dev_info.
55          */
56         if (sb->s_bdev) {
57             struct backing_dev_info *bdi;
58 
59             bdi = sb->s_bdev->bd_inode_backing_dev_info;
60             if (!bdi)
61                 bdi = sb->s_bdev->bd_inode->i_mapping->backing_dev_info;
62             mapping->backing_dev_info = bdi;
63         }
64         inode->i_private = NULL;
65         inode->i_mapping = mapping;
66     }
67     return inode;
68 }

　　 kmem_cache_alloc(inode_cachep, GFP_KERNEL);这儿就是最底层为sys虚拟文件系统分配内存的函数，就是采用了高速页缓存方法，在内存中为节点分配了一块内存。

 1 **
 2  * kmem_cache_alloc - Allocate an object
 3  * @cachep: The cache to allocate from.
 4  * @flags: See kmalloc().
 5  *
 6  * Allocate an object from this cache.  The flags are only relevant
 7  * if the cache has no available objects.
 8  */
 9 void *kmem_cache_alloc(struct kmem_cache *cachep, gfp_t flags)
10 {
11     return __cache_alloc(cachep, flags, __builtin_return_address(0));
12 }

上面是关于sysfs虚拟文件系统的分析，与i2c驱动没有太大的关系，但是我们可以看出来i2c的driver和device最后都是挂在总线上的，这些都是可以归纳为：总线---设备-----驱动模型的，我们可以看出来从i2c_add_driver()函数开始内核不光是在建立一个driver同时也在忙着将这个dirver挂在这个总线上，前面贴出的代码描述了这个过程，下面在看看流程：

　　i2c_add_driver()----------->i2c_register_driver()

　　　　　　　　　　　　　　　　　　　　driver->driver.bus = &i2c_bus_type

 1 struct bus_type i2c_bus_type = {
 2     .name        = "i2c",
 3     .dev_attrs    = i2c_dev_attrs,
 4     .match        = i2c_device_match,
 5     .uevent        = i2c_device_uevent,
 6     .probe        = i2c_device_probe,
 7     .remove        = i2c_device_remove,
 8     .shutdown    = i2c_device_shutdown,
 9     .suspend    = i2c_device_suspend,
10     .resume        = i2c_device_resume,
11 };

　　i2c_driver与i2c_client关系：

　　i2c_driver对应于一套驱动方法，主要成员函数是probe()、remove()、suspend()、resume()。

　　i2c_client对应于真实的物理设备，每个I2C设备都需要一个i2c_client来描述，i2c_driver与i2c_client的关系是一对多，一个i2c_drvier可以支持多个同类型的i2c_client。

　　i2c_adpater与i2c_client关系

　　i2c_adpater与i2c_client的关系与I2C硬件体系中适配器和设备的关系一致，即i2c_client依附于i2c_adapter。一个适配器可以连接多个I2C设备，所以一个i2c_adapter也可以被多个i2c_client依附，i2c_adapter中包括依附于它的i2c_client的链表。

　　刚开始没搞懂其实i2c_client、i2c_adpater这两个数据结构都是内核抽象出来的便于对多平台的适应，每一个i2c_adpater对应于一条总线，i2c_client每一个对应于一个具体设备。

　　网上的解释：简单点了， 你的开发板上有几个I2C接口，就有几个adapter , 也就是有几条I2C bus ，  I2C CLIENT 对应的就是你的外围I2C 设备，有几个就有几个CLIENT , 把这些设备插入开发板， 对应其中的一条BUS, 那么相应的就对应了其中的一个ADAPTER , 接下来的就是  CLIENT 与 ADAPTER 勾搭成对了， 后面就是做该做的事了
　　在编写I2C驱动的时候我们需要实现两个方面的内容：
　　1、提供I2C适配器的硬件驱动，探测、初始化I2C适配器、驱动CPU控制的I2C适配器从硬件上产生各种信号及处理I2C中断。
　　2、提供I2C适配器的算法，用具体适配器的xxx_dfer()函数填充i2c_algorithm的master_xfer指针。
　　3、对I2C core的接口，必须实现 struct i2c_drvier数据结构中的几个特定的功能函数。这些函数是I2C驱动与I2C总线物理层（I2C控制器）和I2C设备器件之间通信的基础。

　　4、 对用户应用层的接口，必须实现struct file_operation数据结构中的一些特定功能的函数，如 open ，release , read ,write，lseek等函数。以上两类接口中，对I2C core的接口是对I2C设备访问的基础，实现对I2C总线具体的访问方法；对用户应用层的接口则是方便应用程序开发，实现设备特定功能的必不可少的部分。例如，如果是字符设备，就实现文件操作接口，实现具体设备yyy的yyy_read()、yyy_write()和yyy_ioctl()函数等；如果是声卡，就实现ALSA驱动。


　　下面的函数流程就是i2c注册的过程，在注册的过程中会把i2c添加到总线上去，同时完成match过程(目前没有弄清楚的流程)，难道是在这儿进行了dev和driver的比较？
　　i2c_add_driver()---------->i2c_register_driver()------------>driver_register()------------------->bus_add_driver()-------->driver_attach()--------->bus_for_each_dev()-------------->__driver_attach()----------------->driver_probe_device()----------------->int (*match)(struct device * dev, struct device_driver * drv)
 　　
　　 总结一下I2C驱动的流程：
　　1、首先，在i2c_client_address_data的normal_i2c属性中定义好我们设备的设备地址。
　　2、接下来，i2c_driver就出场了，它的功能是定义i2c设备的名字，探测函数，卸载函数三个属性。
　　3、当程序在入口函数中注册i2c-driver驱动之后，系统就会根据我们第一步中定义的设备地址，调用attach_adapter函数进行匹配设备地址是否支持，在attach_adapter函数中主要的功能是在调用i2c_probe函数，当系统检测到设备地址匹配时，就会进入i2c_probe函数中干一些重要的事，接着就进入i2c-probe传入的at24cxx_detect函数中实现我们自己的事。

　　其实总结一下就下面一个流程：at24cxx_attach_adapter -> i2c_probe -> at24cxx_detect

　　　当我们卸载设备时，会自动调用i2c_driver中定义的卸载函数at24cxx_detach_adapter进行卸载设备。

　　最后一步自然就是在出口函数中卸载i2c-driver驱动。

　　因为I2C只是一种通信的方式，所以在完成前面的工作后我们需要完成我们要在I2C这种通信方式山所做的工作，我们一般在at24cxx_detect()中完成设备register_chrdev()的注册，然后填写read()、write()等函数。

　　没有弄得很清楚的就是为什么没有注册i2c_add_adapter()---------->i2c_register_adapter()，适配器和device的匹配是在driver中完成的吗？

　　参考的比较经典的博文：http://www.cnblogs.com/lihaiyan/p/4452875.html

　　　　　　　　　　　　　　http://blog.csdn.net/chocolate001/article/details/7470873

　　　　　　　　　　　　　　http://blog.sina.com.cn/s/blog_63f31f340101byb2.html

　　　　　　　　　　　　　　http://www.embedu.org/Column/Column213.htm

posted on 2016-08-14 23:22 FREEH 阅读(1629) 评论(0) 编辑收藏举报