mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-11-26 00:40:55 +07:00
b7565fa3a4
The driver model documentation was added to the kernel tree before struct class was added to <linux/device.h>. Hence this patch that updates the paragraph about struct class in Documentation/driver-model/binding.txt. Signed-off-by: Bart Van Assche <bvanassche@acm.org> Cc: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
99 lines
3.5 KiB
Plaintext
99 lines
3.5 KiB
Plaintext
|
|
Driver Binding
|
|
|
|
Driver binding is the process of associating a device with a device
|
|
driver that can control it. Bus drivers have typically handled this
|
|
because there have been bus-specific structures to represent the
|
|
devices and the drivers. With generic device and device driver
|
|
structures, most of the binding can take place using common code.
|
|
|
|
|
|
Bus
|
|
~~~
|
|
|
|
The bus type structure contains a list of all devices that are on that bus
|
|
type in the system. When device_register is called for a device, it is
|
|
inserted into the end of this list. The bus object also contains a
|
|
list of all drivers of that bus type. When driver_register is called
|
|
for a driver, it is inserted at the end of this list. These are the
|
|
two events which trigger driver binding.
|
|
|
|
|
|
device_register
|
|
~~~~~~~~~~~~~~~
|
|
|
|
When a new device is added, the bus's list of drivers is iterated over
|
|
to find one that supports it. In order to determine that, the device
|
|
ID of the device must match one of the device IDs that the driver
|
|
supports. The format and semantics for comparing IDs is bus-specific.
|
|
Instead of trying to derive a complex state machine and matching
|
|
algorithm, it is up to the bus driver to provide a callback to compare
|
|
a device against the IDs of a driver. The bus returns 1 if a match was
|
|
found; 0 otherwise.
|
|
|
|
int match(struct device * dev, struct device_driver * drv);
|
|
|
|
If a match is found, the device's driver field is set to the driver
|
|
and the driver's probe callback is called. This gives the driver a
|
|
chance to verify that it really does support the hardware, and that
|
|
it's in a working state.
|
|
|
|
Device Class
|
|
~~~~~~~~~~~~
|
|
|
|
Upon the successful completion of probe, the device is registered with
|
|
the class to which it belongs. Device drivers belong to one and only one
|
|
class, and that is set in the driver's devclass field.
|
|
devclass_add_device is called to enumerate the device within the class
|
|
and actually register it with the class, which happens with the
|
|
class's register_dev callback.
|
|
|
|
|
|
Driver
|
|
~~~~~~
|
|
|
|
When a driver is attached to a device, the device is inserted into the
|
|
driver's list of devices.
|
|
|
|
|
|
sysfs
|
|
~~~~~
|
|
|
|
A symlink is created in the bus's 'devices' directory that points to
|
|
the device's directory in the physical hierarchy.
|
|
|
|
A symlink is created in the driver's 'devices' directory that points
|
|
to the device's directory in the physical hierarchy.
|
|
|
|
A directory for the device is created in the class's directory. A
|
|
symlink is created in that directory that points to the device's
|
|
physical location in the sysfs tree.
|
|
|
|
A symlink can be created (though this isn't done yet) in the device's
|
|
physical directory to either its class directory, or the class's
|
|
top-level directory. One can also be created to point to its driver's
|
|
directory also.
|
|
|
|
|
|
driver_register
|
|
~~~~~~~~~~~~~~~
|
|
|
|
The process is almost identical for when a new driver is added.
|
|
The bus's list of devices is iterated over to find a match. Devices
|
|
that already have a driver are skipped. All the devices are iterated
|
|
over, to bind as many devices as possible to the driver.
|
|
|
|
|
|
Removal
|
|
~~~~~~~
|
|
|
|
When a device is removed, the reference count for it will eventually
|
|
go to 0. When it does, the remove callback of the driver is called. It
|
|
is removed from the driver's list of devices and the reference count
|
|
of the driver is decremented. All symlinks between the two are removed.
|
|
|
|
When a driver is removed, the list of devices that it supports is
|
|
iterated over, and the driver's remove callback is called for each
|
|
one. The device is removed from that list and the symlinks removed.
|
|
|