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.Dd January 9, 2025
.Dt DEVICE_IDENTIFY 9
.Os
.Sh NAME
.Nm DEVICE_IDENTIFY
.Nd identify new child devices and register them
.Sh SYNOPSIS
.In sys/param.h
.In sys/bus.h
.Ft void
.Fn DEVICE_IDENTIFY "driver_t *driver" "device_t parent"
.Sh DESCRIPTION
The identify method of a device driver is used to add devices that cannot be
enumerated by the standard method on a bus device.
Devices can be enumerated in various ways including accessing non-ambiguous
device registers and parsing firmware tables.
Software-only pseudo devices are also often enumerated via identify methods.
.Pp
For each newly identified device,
a new device instance should be created by invoking the
.Xr BUS_ADD_CHILD 9
method.
If the identify method is able to discover other properties about the new
device, those should also be set.
For example, device resources should be added to the device by calling
.Xr bus_set_resource 9
for each resource.
.Pp
An identify method might be invoked multiple times.
If a device driver is unloaded and loaded,
the identify method will be called a second time after being reloaded.
As a result, the identify method should avoid duplicate devices.
Devices added by identify methods typically use a fixed device name
in which case
.Xr device_find_child 9
can be used to detect existing devices.
.Sh EXAMPLES
The following pseudo-code shows an example of a function that
probes for a piece of hardware and registers it and its resource
(an I/O port) with the parent bus device.
.Bd -literal
void
foo_identify(driver_t *driver, device_t parent)
{
	device_t child;

	retrieve_device_information;
	if (devices matches one of your supported devices &&
	    device_get_child(parent, "foo", DEVICE_UNIT_ANY) == NULL) {
		child = BUS_ADD_CHILD(parent, 0, "foo", DEVICE_UNIT_ANY);
		bus_set_resource(child, SYS_RES_IOPORT, 0, FOO_IOADDR, 1);
	}
}
.Ed
.Sh SEE ALSO
.Xr BUS_ADD_CHILD 9 ,
.Xr bus_set_resource 9 ,
.Xr device 9 ,
.Xr device_find_child 9
.Sh AUTHORS
This manual page was written by
.An Alexander Langer Aq Mt alex@FreeBSD.org .