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diff --git a/Documentation/driver-model/overview.txt b/Documentation/driver-model/overview.txt deleted file mode 100644 index 6a8f9a8075d8..000000000000 --- a/Documentation/driver-model/overview.txt +++ /dev/null @@ -1,123 +0,0 @@ -The Linux Kernel Device Model - -Patrick Mochel <mochel@digitalimplant.org> - -Drafted 26 August 2002 -Updated 31 January 2006 - - -Overview -~~~~~~~~ - -The Linux Kernel Driver Model is a unification of all the disparate driver -models that were previously used in the kernel. It is intended to augment the -bus-specific drivers for bridges and devices by consolidating a set of data -and operations into globally accessible data structures. - -Traditional driver models implemented some sort of tree-like structure -(sometimes just a list) for the devices they control. There wasn't any -uniformity across the different bus types. - -The current driver model provides a common, uniform data model for describing -a bus and the devices that can appear under the bus. The unified bus -model includes a set of common attributes which all busses carry, and a set -of common callbacks, such as device discovery during bus probing, bus -shutdown, bus power management, etc. - -The common device and bridge interface reflects the goals of the modern -computer: namely the ability to do seamless device "plug and play", power -management, and hot plug. In particular, the model dictated by Intel and -Microsoft (namely ACPI) ensures that almost every device on almost any bus -on an x86-compatible system can work within this paradigm. Of course, -not every bus is able to support all such operations, although most -buses support most of those operations. - - -Downstream Access -~~~~~~~~~~~~~~~~~ - -Common data fields have been moved out of individual bus layers into a common -data structure. These fields must still be accessed by the bus layers, -and sometimes by the device-specific drivers. - -Other bus layers are encouraged to do what has been done for the PCI layer. -struct pci_dev now looks like this: - -struct pci_dev { - ... - - struct device dev; /* Generic device interface */ - ... -}; - -Note first that the struct device dev within the struct pci_dev is -statically allocated. This means only one allocation on device discovery. - -Note also that that struct device dev is not necessarily defined at the -front of the pci_dev structure. This is to make people think about what -they're doing when switching between the bus driver and the global driver, -and to discourage meaningless and incorrect casts between the two. - -The PCI bus layer freely accesses the fields of struct device. It knows about -the structure of struct pci_dev, and it should know the structure of struct -device. Individual PCI device drivers that have been converted to the current -driver model generally do not and should not touch the fields of struct device, -unless there is a compelling reason to do so. - -The above abstraction prevents unnecessary pain during transitional phases. -If it were not done this way, then when a field was renamed or removed, every -downstream driver would break. On the other hand, if only the bus layer -(and not the device layer) accesses the struct device, it is only the bus -layer that needs to change. - - -User Interface -~~~~~~~~~~~~~~ - -By virtue of having a complete hierarchical view of all the devices in the -system, exporting a complete hierarchical view to userspace becomes relatively -easy. This has been accomplished by implementing a special purpose virtual -file system named sysfs. - -Almost all mainstream Linux distros mount this filesystem automatically; you -can see some variation of the following in the output of the "mount" command: - -$ mount -... -none on /sys type sysfs (rw,noexec,nosuid,nodev) -... -$ - -The auto-mounting of sysfs is typically accomplished by an entry similar to -the following in the /etc/fstab file: - -none /sys sysfs defaults 0 0 - -or something similar in the /lib/init/fstab file on Debian-based systems: - -none /sys sysfs nodev,noexec,nosuid 0 0 - -If sysfs is not automatically mounted, you can always do it manually with: - -# mount -t sysfs sysfs /sys - -Whenever a device is inserted into the tree, a directory is created for it. -This directory may be populated at each layer of discovery - the global layer, -the bus layer, or the device layer. - -The global layer currently creates two files - 'name' and 'power'. The -former only reports the name of the device. The latter reports the -current power state of the device. It will also be used to set the current -power state. - -The bus layer may also create files for the devices it finds while probing the -bus. For example, the PCI layer currently creates 'irq' and 'resource' files -for each PCI device. - -A device-specific driver may also export files in its directory to expose -device-specific data or tunable interfaces. - -More information about the sysfs directory layout can be found in -the other documents in this directory and in the file -Documentation/filesystems/sysfs.txt. - |