Merge git://git.kernel.org/pub/scm/linux/kernel/git/brodo/pcmcia-2.6

[pandora-kernel.git] / Documentation / driver-model / overview.txt

diff --git a/Documentation/driver-model/overview.txt b/Documentation/driver-model/overview.txt
index ac4a7a7..6a8f9a8 100644 (file)
--- a/Documentation/driver-model/overview.txt
+++ b/Documentation/driver-model/overview.txt
@@ -18,7 +18,7 @@ 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.
 
 (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 comon, uniform data model for describing
+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
 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


@@ -30,7 +30,7 @@ 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
 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.
+buses support most of those operations.

 
 
 Downstream Access
 
 
 Downstream Access


@@ -46,25 +46,29 @@ struct pci_dev now looks like this:
 struct pci_dev {
        ...
 
 struct pci_dev {
        ...
 

-       struct device dev;
+       struct device dev;     /* Generic device interface */
+       ...

 };
 
 };
 

-Note first that it is statically allocated. This means only one allocation on
-device discovery. Note also that it is at the _end_ of struct pci_dev. This is
-to make people think about what they're doing when switching between the bus
-driver and the global driver; and to prevent against mindless casts between
-the two.
+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
 
 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 the the current
+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,
 driver model generally do not and should not touch the fields of struct device,

-unless there is a strong compelling reason to do so.
+unless there is a 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
-will break. On the other hand, if only the bus layer (and not the device
-layer) accesses struct device, it is only that layer that needs to change.
+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
 
 
 User Interface


@@ -73,15 +77,27 @@ 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
 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. It is hence possible for the user to mount the
-whole sysfs filesystem anywhere in userspace.
+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

 
 

-This can be done permanently by providing the following entry into the
-/etc/fstab (under the provision that the mount point does exist, of course):
+or something similar in the /lib/init/fstab file on Debian-based systems:

 
 

-none           /sys    sysfs    defaults               0       0
+none            /sys    sysfs    nodev,noexec,nosuid    0 0

 
 

-Or by hand on the command line:
+If sysfs is not automatically mounted, you can always do it manually with:

 
 # mount -t sysfs sysfs /sys
 
 
 # mount -t sysfs sysfs /sys