Commit ab11f899 authored by Linas Vepstas's avatar Linas Vepstas Committed by Linus Torvalds

[PATCH] Clean up Documentation/driver-model/overview.txt

Edits to the driver-model documentation for grammar, clarity and content.

These docs haven't been updated in years, and some of the technical content
and discussion has become stale; this patch updates these.  In addition,
some of the language is awkward.  Fix this.

(I'm trying to cleanup the other files in this directory also,
patches for these will come a bit later).
Signed-off-by: default avatarLinas Vepstas <linas@austin.ibm.com>
Acked-by: default avatarPatrick Mochel <mochel@digitalimplant.org>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 1989e20c
The Linux Kernel Device Model
Patrick Mochel <mochel@osdl.org>
Patrick Mochel <mochel@digitalimplant.org>
26 August 2002
Drafted 26 August 2002
Updated 31 January 2006
Overview
~~~~~~~~
This driver model is a unification of all the current, disparate driver models
that are currently in the kernel. It is intended to augment the
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.
Current driver models implement some sort of tree-like structure (sometimes
just a list) for the devices they control. But, there is no linkage between
the different bus types.
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.
A common data structure can provide this linkage with little overhead: when a
bus driver discovers a particular device, it can insert it into the global
tree as well as its local tree. In fact, the local tree becomes just a subset
of the global tree.
Common data fields can also be moved out of the local bus models into the
global model. Some of the manipulations of these fields can also be
consolidated. Most likely, manipulation functions will become a set
of helper functions, which the bus drivers wrap around to include any
bus-specific items.
The common device and bridge interface currently reflects the goals of the
modern PC: namely the ability to do seamless Plug and Play, power management,
and hot plug. (The model dictated by Intel and Microsoft (read: ACPI) ensures
us that any device in the system may fit any of these criteria.)
In reality, not every bus will be able to support such operations. But, most
buses will support a majority of those operations, and all future buses will.
In other words, a bus that doesn't support an operation is the exception,
instead of the other way around.
The current driver model provides a comon, 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 a most of those operations.
Downstream Access
~~~~~~~~~~~~~~~~~
Common data fields have been moved out of individual bus layers into a common
data structure. But, these fields must still be accessed by the bus layers,
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.
......@@ -53,7 +46,7 @@ struct pci_dev now looks like this:
struct pci_dev {
...
struct device device;
struct device dev;
};
Note first that it is statically allocated. This means only one allocation on
......@@ -64,9 +57,9 @@ 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. PCI devices that have been converted generally do not touch the fields
of struct device. More precisely, device-specific drivers should not touch
fields of struct device unless there is a strong compelling reason to do so.
device. Individual PCI device drivers that have been converted the the current
driver model generally do not and should not touch the fields of struct device,
unless there is a strong compelling reason to do so.
This abstraction is prevention of unnecessary pain during transitional phases.
If the name of the field changes or is removed, then every downstream driver
......
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