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Diffstat (limited to 'Documentation/driver-model/device.txt')
| -rw-r--r-- | Documentation/driver-model/device.txt | 146 |
1 files changed, 44 insertions, 102 deletions
diff --git a/Documentation/driver-model/device.txt b/Documentation/driver-model/device.txt index a7cbfff40d0..1e70220d20f 100644 --- a/Documentation/driver-model/device.txt +++ b/Documentation/driver-model/device.txt @@ -2,96 +2,7 @@ The Basic Device Structure ~~~~~~~~~~~~~~~~~~~~~~~~~~ -struct device { - struct list_head g_list; - struct list_head node; - struct list_head bus_list; - struct list_head driver_list; - struct list_head intf_list; - struct list_head children; - struct device * parent; - - char name[DEVICE_NAME_SIZE]; - char bus_id[BUS_ID_SIZE]; - - spinlock_t lock; - atomic_t refcount; - - struct bus_type * bus; - struct driver_dir_entry dir; - - u32 class_num; - - struct device_driver *driver; - void *driver_data; - void *platform_data; - - u32 current_state; - unsigned char *saved_state; - - void (*release)(struct device * dev); -}; - -Fields -~~~~~~ -g_list: Node in the global device list. - -node: Node in device's parent's children list. - -bus_list: Node in device's bus's devices list. - -driver_list: Node in device's driver's devices list. - -intf_list: List of intf_data. There is one structure allocated for - each interface that the device supports. - -children: List of child devices. - -parent: *** FIXME *** - -name: ASCII description of device. - Example: " 3Com Corporation 3c905 100BaseTX [Boomerang]" - -bus_id: ASCII representation of device's bus position. This - field should be a name unique across all devices on the - bus type the device belongs to. - - Example: PCI bus_ids are in the form of - <bus number>:<slot number>.<function number> - This name is unique across all PCI devices in the system. - -lock: Spinlock for the device. - -refcount: Reference count on the device. - -bus: Pointer to struct bus_type that device belongs to. - -dir: Device's sysfs directory. - -class_num: Class-enumerated value of the device. - -driver: Pointer to struct device_driver that controls the device. - -driver_data: Driver-specific data. - -platform_data: Platform data specific to the device. - - Example: for devices on custom boards, as typical of embedded - and SOC based hardware, Linux often uses platform_data to point - to board-specific structures describing devices and how they - are wired. That can include what ports are available, chip - variants, which GPIO pins act in what additional roles, and so - on. This shrinks the "Board Support Packages" (BSPs) and - minimizes board-specific #ifdefs in drivers. - -current_state: Current power state of the device. - -saved_state: Pointer to saved state of the device. This is usable by - the device driver controlling the device. - -release: Callback to free the device after all references have - gone away. This should be set by the allocator of the - device (i.e. the bus driver that discovered the device). +See the kerneldoc for the struct device. Programming Interface @@ -134,31 +45,62 @@ struct device_attribute { const char *buf, size_t count); }; -Attributes of devices can be exported via drivers using a simple -procfs-like interface. +Attributes of devices can be exported by a device driver through sysfs. Please see Documentation/filesystems/sysfs.txt for more information on how sysfs works. +As explained in Documentation/kobject.txt, device attributes must be be +created before the KOBJ_ADD uevent is generated. The only way to realize +that is by defining an attribute group. + Attributes are declared using a macro called DEVICE_ATTR: #define DEVICE_ATTR(name,mode,show,store) Example: -DEVICE_ATTR(power,0644,show_power,store_power); +static DEVICE_ATTR(type, 0444, show_type, NULL); +static DEVICE_ATTR(power, 0644, show_power, store_power); -This declares a structure of type struct device_attribute named -'dev_attr_power'. This can then be added and removed to the device's -directory using: +This declares two structures of type struct device_attribute with respective +names 'dev_attr_type' and 'dev_attr_power'. These two attributes can be +organized as follows into a group: -int device_create_file(struct device *device, struct device_attribute * entry); -void device_remove_file(struct device * dev, struct device_attribute * attr); +static struct attribute *dev_attrs[] = { + &dev_attr_type.attr, + &dev_attr_power.attr, + NULL, +}; -Example: +static struct attribute_group dev_attr_group = { + .attrs = dev_attrs, +}; + +static const struct attribute_group *dev_attr_groups[] = { + &dev_attr_group, + NULL, +}; + +This array of groups can then be associated with a device by setting the +group pointer in struct device before device_register() is invoked: + + dev->groups = dev_attr_groups; + device_register(dev); -device_create_file(dev,&dev_attr_power); -device_remove_file(dev,&dev_attr_power); +The device_register() function will use the 'groups' pointer to create the +device attributes and the device_unregister() function will use this pointer +to remove the device attributes. -The file name will be 'power' with a mode of 0644 (-rw-r--r--). +Word of warning: While the kernel allows device_create_file() and +device_remove_file() to be called on a device at any time, userspace has +strict expectations on when attributes get created. When a new device is +registered in the kernel, a uevent is generated to notify userspace (like +udev) that a new device is available. If attributes are added after the +device is registered, then userspace won't get notified and userspace will +not know about the new attributes. +This is important for device driver that need to publish additional +attributes for a device at driver probe time. If the device driver simply +calls device_create_file() on the device structure passed to it, then +userspace will never be notified of the new attributes. |