LDD3 notes: Driver Model

My notes while reading Linux Device Drivers 3rd edition.

2.6 device model addresses aspects common to all types of devices:

• Power management
• Userspace communications /sysfs
• Hotplugging w/ udev
• Device classes
• Object lifecycle

Kobject, Kset, Subsystem

• kobject per object, belongs to a ktype.
• kset for a collection of kobjects of same type
• Subsystem as a high-level portion of the kernel as a whole: block, devices, usb, pci
• Class as high-level view of what a device does

Kobject

• embed struct kobject in your structure
• initialize name, ktype, kset and parent
  
• implement a destructor (release)
• implement reference counting by wrapping kobject_{get|put}
• back-cast kobject references to your structure using using container_of()

Adding a Kobject to a Kset

• point kobject.kset to set
• point kobject.parent to the set
  
• kobject_register()

Subsystem

• a kset with a semaphore
• rooted at the top of the sysfs hierarchy
• subsystem_{init|register|unregister|get|put}

Bus, Device, Driver, Class, Class device

• Bus as a channel between processor and devices: physical or virtual
  
• Device as an instance to be controlled by a driver, connected to a bus
  
• Driver
  

Bus type

• bus_[un]register() - confusing name
• match - compare whether a given device can be handled by the given driver
• typically implement bus type specific functions to register devices to a specific bus instance
  
• on bus enumeration
• on platform initialization
  

Bus instance

• each instance is a device
• bus_id naming the bus instance
• parent and/or bus could be null for a singleton top level bus, parent could be the host controller

Device

• parent pointers reflect a tree of device attachments through buses and host controllers
  
• bus_id for unique identification within a bus
• type of bus, for matching devices and drivers
  
• driver and driver private data

Class & Class device

• Typically handled by high-level code when you register some facilities you implement
• Device membership in a class is represented by a struct class_device

Attributes

Kobject Attributes, low-level interface

• struct attribute: owner module and filesystem mode.
  
• sysfs_ops: show/store
• sysfs_create[_bin]_[file|link]
  

Attributes for high-level objects

• [bus|driver|device]_create_file
  
• BUS_ATTR(name,mode,show,store)
• DRIVER_ATTR()
• DEVICE_ATTR()
  
• CLASS_DEVICE_ATTR()

Firmware

Driver

• request_firmware(name)
• release_firmware()

Userspace reacts to hotplug and special sysfs files

• loading state
• binary data
• device identification

Probably implemented in udev?