141 lines
5.2 KiB
Groff
141 lines
5.2 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 February 8, 2012
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.Dt DEVICE_PROBE 9
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.Os
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.Sh NAME
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.Nm DEVICE_PROBE
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.Nd probe for device existence
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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 int
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.Fn DEVICE_PROBE "device_t dev"
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.Sh DESCRIPTION
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The
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.Fn DEVICE_PROBE
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method should probe to see if the device is present.
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It should return 0 if the device exists,
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.Er ENXIO
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if it cannot be found.
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If some other error happens during the probe (such as a memory
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allocation failure), an appropriate error code should be returned.
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For
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cases where more than one driver matches a device, a priority value can
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be returned.
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In this case, success codes are values less than or equal
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to zero with the highest value representing the best match.
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Failure
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codes are represented by positive values and the regular
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.Ux
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error
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codes should be used for the purpose.
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.Pp
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If a driver returns a success code which is less than zero, it must
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not assume that it will be the same driver which is attached to the
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device.
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In particular, it must not assume that any values stored in
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the softc structure will be available for its attach method and any
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resources allocated during probe must be released and re-allocated
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if the attach method is called.
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In addition it is an absolute requirement that the probe routine have
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no side effects whatsoever.
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The probe routine may be called more than once before the attach
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routine is called.
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.Pp
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If a success code of zero is
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returned, the driver can assume that it will be the one attached, but
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must not hold any resources when the probe routine returns.
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A driver may assume that the softc is preserved when it returns
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a success code of zero.
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.Sh RETURN VALUES
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A value equal to or less than zero indicates success, greater than
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zero indicates an error (errno).
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For values equal to or less than
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zero: zero indicates highest priority, no further probing is done;
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for a value less than zero, the lower the value the lower the
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priority, e.g.\& -100 indicates a lower priority than -50.
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.Pp
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The following values are used by convention to indicate different
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strengths of matching in a probe routine.
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Except as noted, these are just suggested values, and there's nothing
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magical about them.
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.Bl -tag -width BUS_PROBE_NOWILDCARD
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.It BUS_PROBE_SPECIFIC
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The device that cannot be reprobed, and that no
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possible other driver may exist (typically legacy drivers who don't follow
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all the rules, or special needs drivers).
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.It BUS_PROBE_VENDOR
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The device is supported by a vendor driver.
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This is for source or binary drivers that are not yet integrated into the
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.Fx
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tree.
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Its use in the base OS is prohibited.
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.It BUS_PROBE_DEFAULT
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The device is a normal device matching some plug and play ID.
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This is
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the normal return value for drivers to use.
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It is intended that nearly all of the drivers in the tree should return
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this value.
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.It BUS_PROBE_LOW_PRIORITY
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The driver is a legacy driver, or an otherwise less desirable driver
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for a given plug and play ID.
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The driver has special requirements like when there are two drivers
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that support overlapping series of hardware devices.
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In this case the one that supports the older part of the line would
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return this value, while the one that supports the newer ones would
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return BUS_PROBE_DEFAULT.
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.It BUS_PROBE_GENERIC
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The driver matches the type of device generally.
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This allows drivers to match all serial ports generally, with specialized
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drivers matching particular types of serial ports that need special
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treatment for some reason.
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.It BUS_PROBE_HOOVER
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The driver matches all unclaimed devices on a bus.
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The
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.Xr ugen 4
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device is one example.
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.It BUS_PROBE_NOWILDCARD
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The driver expects its parent to tell it which children to manage
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and no probing is really done.
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The device only matches if its parent bus specifically said to use
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this driver.
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.El
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.Sh SEE ALSO
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.Xr device 9 ,
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.Xr DEVICE_ATTACH 9 ,
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.Xr DEVICE_DETACH 9 ,
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.Xr DEVICE_IDENTIFY 9 ,
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.Xr DEVICE_SHUTDOWN 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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