DEVICE_IDENTIFY.9

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.Dd January 15, 2017
.Dt DEVICE_IDENTIFY 9
.Os
.Sh NAME
.Nm DEVICE_IDENTIFY
.Nd identify a device, register it
.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 function for a device is only needed for devices on buses
that cannot identify their children independently, e.g.\& the ISA bus.
It is used to recognize the device (usually done by accessing non-ambiguous
registers in the hardware) and to tell the kernel about it and thus
creating a new device instance.
.Pp
.Xr BUS_ADD_CHILD 9
is used to register the device as a child of the bus.
The device's resources (such as IRQ and I/O ports) are registered
with the kernel by calling
.Fn bus_set_resource
for each resource (refer to
.Xr bus_set_resource 9
for more information).
.Pp
Since the device tree and the device driver tree are disjoint, the
.Fn DEVICE_IDENTIFY
routine needs to take this into account.
If you load and unload your device driver that has the identify
routine, the child node has the potential for adding the same node
multiple times unless specific measure are taken to preclude that
possibility.
.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 kernel.
.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 &&
	    not already in device tree) {
		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_add_child 9 ,
.Xr DEVICE_ATTACH 9 ,
.Xr DEVICE_DETACH 9 ,
.Xr DEVICE_PROBE 9 ,
.Xr DEVICE_SHUTDOWN 9
.Sh AUTHORS
This manual page was written by
.An Alexander Langer Aq Mt alex@FreeBSD.org .