35a45e42cd
BUS_ADD_CHILD. Make it explicit since it follows the command paradigm rather than the callback paradigm. Add other clarifying notes as well.
134 lines
4.6 KiB
Groff
134 lines
4.6 KiB
Groff
.\" -*- nroff -*-
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.\"
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.\" Copyright (c) 1998 Doug Rabson
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.\"
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.\" All rights reserved.
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.\"
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.\" This program is free software.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd October 28, 2015
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.Dt DEVICE_ADD_CHILD 9
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.Os
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.Sh NAME
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.Nm device_add_child ,
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.Nm device_add_child_ordered
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.Nd "add a new device as a child of an existing device"
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/bus.h
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.Ft device_t
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.Fn device_add_child "device_t dev" "const char *name" "int unit"
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.Ft device_t
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.Fn device_add_child_ordered "device_t dev" "int order" "const char *name" "int unit"
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.Sh DESCRIPTION
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Create a new child device of
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.Fa dev .
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The
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.Fa name
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and
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.Fa unit
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arguments specify the name and unit number of the device.
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If the name is unknown then the caller should pass
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.Dv NULL .
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If the unit is unknown then the caller should pass
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.Dv -1
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and the system will choose the next available unit number.
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.Pp
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The name of the device is used to determine which drivers might be
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appropriate for the device.
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If a name is specified then only drivers of that name are probed.
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If no name is given then all drivers for the owning bus are probed.
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In any event, only the name of the device is stored so that one may
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safely unload/load a driver bound to that name.
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.Pp
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This allows busses which can uniquely identify device instances (such
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as PCI) to allow each driver to check each device instance for a
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match.
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For busses which rely on supplied probe hints where only one
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driver can have a chance of probing the device, the driver name should
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be specified as the device name.
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.Pp
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Normally unit numbers will be chosen automatically by the system and a
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unit number of
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.Dv -1
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should be given.
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When a specific unit number is desired (e.g.,\& for wiring a particular
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piece of hardware to a pre-configured unit number), that unit should
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be passed.
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If the specified unit number is already allocated, a new
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unit will be allocated and a diagnostic message printed.
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.Pp
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If the devices attached to a bus must be probed in a specific order
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(e.g.,\& for the ISA bus some devices are sensitive to failed probe attempts
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of unrelated drivers and therefore must be probed first),
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the
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.Fa order
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argument of
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.Fn device_add_child_ordered
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should be used to specify a partial ordering.
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The new device will be added before any existing device with a greater
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order.
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If
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.Fn device_add_child
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is used, then the new child will be added as if its order was zero.
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.Pp
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When adding a device in the context of
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.Xr DEVICE_IDENTIFY 9
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routine, the
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.Xr device_find_child 9
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routine should be used to ensure that the device has not already been
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added to the tree.
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Because the device name and
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.Vt devclass_t
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are associated at probe time (not child addition time), previous
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instances of the driver (say in a module that was later unloaded) may
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have already added the instance.
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Authors of bus drivers must likewise be careful when adding children
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when they are loaded and unloaded to avoid duplication of children
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devices.
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.Pp
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When adding a child to another device node, such as in an identify
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routine, use
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.Xr BUS_ADD_CHILD 9
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instead of
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.Xr device_add_child 9 .
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.Xr BUS_ADD_CHILD 9
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will call
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.Xr device_add_child 9
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and add the proper bus-specific data to the new child.
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.Fn device_add_child
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does not call
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.Xr BUS_ADD_CHILD 9 .
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.Sh RETURN VALUES
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The new device if successful, NULL otherwise.
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.Sh SEE ALSO
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.Xr BUS_ADD_CHILD 9 ,
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.Xr device 9 ,
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.Xr device_find_child 9 ,
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.Xr DEVICE_IDENTIFY 9
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.Sh AUTHORS
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This manual page was written by
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.An Doug Rabson .
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