diff options
Diffstat (limited to 'drivers/i2c/i2c-dev.c')
| -rw-r--r-- | drivers/i2c/i2c-dev.c | 60 |
1 files changed, 59 insertions, 1 deletions
diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c index 5a15e50748de..7360f9c37256 100644 --- a/drivers/i2c/i2c-dev.c +++ b/drivers/i2c/i2c-dev.c @@ -38,6 +38,15 @@ static struct i2c_driver i2cdev_driver; +/* + * An i2c_dev represents an i2c_adapter ... an I2C or SMBus master, not a + * slave (i2c_client) with which messages will be exchanged. It's coupled + * with a character special file which is accessed by user mode drivers. + * + * The list of i2c_dev structures is parallel to the i2c_adapter lists + * maintained by the driver model, and is updated using notifications + * delivered to the i2cdev_driver. + */ struct i2c_dev { struct list_head list; struct i2c_adapter *adap; @@ -103,6 +112,25 @@ static ssize_t show_adapter_name(struct device *dev, } static DEVICE_ATTR(name, S_IRUGO, show_adapter_name, NULL); +/* ------------------------------------------------------------------------- */ + +/* + * After opening an instance of this character special file, a file + * descriptor starts out associated only with an i2c_adapter (and bus). + * + * Using the I2C_RDWR ioctl(), you can then *immediately* issue i2c_msg + * traffic to any devices on the bus used by that adapter. That's because + * the i2c_msg vectors embed all the addressing information they need, and + * are submitted directly to an i2c_adapter. However, SMBus-only adapters + * don't support that interface. + * + * To use read()/write() system calls on that file descriptor, or to use + * SMBus interfaces (and work with SMBus-only hosts!), you must first issue + * an I2C_SLAVE (or I2C_SLAVE_FORCE) ioctl. That configures an anonymous + * (never registered) i2c_client so it holds the addressing information + * needed by those system calls and by this SMBus interface. + */ + static ssize_t i2cdev_read (struct file *file, char __user *buf, size_t count, loff_t *offset) { @@ -172,6 +200,16 @@ static int i2cdev_ioctl(struct inode *inode, struct file *file, switch ( cmd ) { case I2C_SLAVE: case I2C_SLAVE_FORCE: + /* NOTE: devices set up to work with "new style" drivers + * can't use I2C_SLAVE, even when the device node is not + * bound to a driver. Only I2C_SLAVE_FORCE will work. + * + * Setting the PEC flag here won't affect kernel drivers, + * which will be using the i2c_client node registered with + * the driver model core. Likewise, when that client has + * the PEC flag already set, the i2c-dev driver won't see + * (or use) this setting. + */ if ((arg > 0x3ff) || (((client->flags & I2C_M_TEN) == 0) && arg > 0x7f)) return -EINVAL; @@ -386,6 +424,13 @@ static int i2cdev_open(struct inode *inode, struct file *file) if (!adap) return -ENODEV; + /* This creates an anonymous i2c_client, which may later be + * pointed to some address using I2C_SLAVE or I2C_SLAVE_FORCE. + * + * This client is ** NEVER REGISTERED ** with the driver model + * or I2C core code!! It just holds private copies of addressing + * information and maybe a PEC flag. + */ client = kzalloc(sizeof(*client), GFP_KERNEL); if (!client) { i2c_put_adapter(adap); @@ -394,7 +439,6 @@ static int i2cdev_open(struct inode *inode, struct file *file) snprintf(client->name, I2C_NAME_SIZE, "i2c-dev %d", adap->nr); client->driver = &i2cdev_driver; - /* registered with adapter, passed as client to user */ client->adapter = adap; file->private_data = client; @@ -422,6 +466,14 @@ static const struct file_operations i2cdev_fops = { .release = i2cdev_release, }; +/* ------------------------------------------------------------------------- */ + +/* + * The legacy "i2cdev_driver" is used primarily to get notifications when + * I2C adapters are added or removed, so that each one gets an i2c_dev + * and is thus made available to userspace driver code. + */ + static struct class *i2c_dev_class; static int i2cdev_attach_adapter(struct i2c_adapter *adap) @@ -486,6 +538,12 @@ static struct i2c_driver i2cdev_driver = { .detach_client = i2cdev_detach_client, }; +/* ------------------------------------------------------------------------- */ + +/* + * module load/unload record keeping + */ + static int __init i2c_dev_init(void) { int res; |