xref: /freebsd/share/man/man9/DEVICE_PROBE.9 (revision aa0a1e58)
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31.Dd March 3, 2008
32.Dt DEVICE_PROBE 9
33.Os
34.Sh NAME
35.Nm DEVICE_PROBE
36.Nd probe for device existence
37.Sh SYNOPSIS
38.In sys/param.h
39.In sys/bus.h
40.Ft int
41.Fn DEVICE_PROBE "device_t dev"
42.Sh DESCRIPTION
43The
44.Fn DEVICE_PROBE
45method should probe to see if the device is present.
46It should return 0 if the device exists,
47.Er ENXIO
48if it cannot be found.
49If some other error happens during the probe (such as a memory
50allocation failure), an appropriate error code should be returned.
51For
52cases where more than one driver matches a device, a priority value can
53be returned.
54In this case, success codes are values less than or equal
55to zero with the highest value representing the best match.
56Failure
57codes are represented by positive values and the regular
58.Ux
59error
60codes should be used for the purpose.
61.Pp
62If a driver returns a success code which is less than zero, it must
63not assume that it will be the same driver which is attached to the
64device.
65In particular, it must not assume that any values stored in
66the softc structure will be available for its attach method and any
67resources allocated during probe must be released and re-allocated
68if the attach method is called.
69In addition it is an absolute requirement that the probe routine have
70no side effects whatsoever.
71The probe routine may be called more than once before the attach
72routine is called.
73.Pp
74If a success code of zero is
75returned, the driver can assume that it will be the one attached, but
76must not hold any resources when the probe routine returns.
77A driver may assume that the softc is preserved when it returns
78a success code of zero.
79.Sh RETURN VALUES
80A value equal to or less than zero indicates success, greater than
81zero indicates an error (errno).
82For values equal to or less than
83zero: zero indicates highest priority, no further probing is done;
84for a value less than zero, the lower the value the lower the
85priority, e.g.\& -100 indicates a lower priority than -50.
86.Pp
87The following values are used by convention to indicate different
88strengths of matching in a probe routine.
89Except as noted, these are just suggested values, and there's nothing
90magical about them.
91.Bl -tag -width BUS_PROBE_NOWILDCARD
92.It BUS_PROBE_SPECIFIC
93The device that cannot be reprobed, and that no
94possible other driver may exist (typically legacy drivers who don't follow
95all the rules, or special needs drivers).
96.It BUS_PROBE_VENDOR
97The device is supported by a vendor driver.
98This is for source or binary drivers that are not yet integrated into the
99.Fx
100tree.
101Its use in the base OS is prohibited.
102.It BUS_PROBE_DEFAULT
103The device is a normal device matching some plug and play ID.  This is
104the normal return value for drivers to use.
105It is intended that nearly all of the drivers in the tree should return
106this value.
107.It BUS_PROBE_LOW_PRIORITY
108The driver is a legacy driver, or an otherwise less desirable driver
109for a given plug and play ID.
110The driver has special requirements like when there are two drivers
111that support overlapping series of hardware devices.
112In this case the one that supports the older part of the line would
113return this value, while the one that supports the newer ones would
114return BUS_PROBE_DEFAULT.
115.It BUS_PROBE_GENERIC
116The driver matches the type of device generally.
117This allows drivers to match all serial ports generally, with specialized
118drivers matching particular types of serial ports that need special
119treatment for some reason.
120.It BUS_PROBE_HOOVER
121The driver matches all unclaimed devices on a bus.
122The
123.Xr ugen 5
124device is one example.
125.It BUS_PROBE_NOWILDCARD
126The driver expects its parent to tell it which children to manage
127and no probing is really done.
128The device only matches if its parent bus specifically said to use
129this driver.
130.El
131.Sh SEE ALSO
132.Xr device 9 ,
133.Xr DEVICE_ATTACH 9 ,
134.Xr DEVICE_DETACH 9 ,
135.Xr DEVICE_IDENTIFY 9 ,
136.Xr DEVICE_SHUTDOWN 9
137.Sh AUTHORS
138This manual page was written by
139.An Doug Rabson .
140