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.Dd August 7, 2021
.Dt AUTOCONF 9
.Os
.Sh NAME
.Nm autoconf ,
.Nm config_search ,
.Nm config_found ,
.Nm config_match ,
.Nm config_attach ,
.Nm config_attach_pseudo ,
.Nm config_detach ,
.Nm config_detach_children ,
.Nm config_deactivate ,
.Nm config_defer ,
.Nm config_interrupts ,
.Nm config_mountroot ,
.Nm config_pending_incr ,
.Nm config_pending_decr ,
.Nm config_finalize_register
.Nd autoconfiguration framework
.Sh SYNOPSIS
.In sys/param.h
.In sys/device.h
.In sys/errno.h
.Ft cfdata_t
.Fn config_search "device_t parent" "void *aux" "const struct cfargs *"
.Ft device_t
.Fn config_found "device_t parent" "void *aux" "cfprint_t print" \
"const struct cfargs *"
.Ft int
.Fn config_match "device_t parent" "cfdata_t cf" "void *aux"
.Ft int
.Fn config_probe "device_t parent" "cfdata_t cf" "void *aux"
.Ft device_t
.Fn config_attach "device_t parent" "cfdata_t cf" "void *aux" \
"cfprint_t print" "const struct cfargs *"
.Ft device_t
.Fn config_attach_pseudo "cfdata_t cf"
.Ft int
.Fn config_detach "device_t dev" "int flags"
.Ft int
.Fn config_detach_children "device_t dev" "int flags"
.Ft int
.Fn config_deactivate "device_t dev"
.Ft int
.Fn config_defer "device_t dev" "void (*func)(device_t)"
.Ft void
.Fn config_interrupts "device_t dev" "void (*func)(device_t)"
.Ft void
.Fn config_mountroot "device_t dev" "void (*func)(device_t)"
.Ft void
.Fn config_pending_incr
.Ft void
.Fn config_pending_decr
.Ft int
.Fn config_finalize_register "device_t dev" "int (*func)(device_t)"
.Sh DESCRIPTION
Autoconfiguration is the process of matching hardware devices with an
appropriate device driver.
In its most basic form, autoconfiguration consists of the recursive process
of finding and attaching all devices on a bus, including other busses.
.Pp
The autoconfiguration framework supports
.Em direct configuration
where the bus driver can determine the devices present.
The autoconfiguration framework also supports
.Em indirect configuration
where the drivers must probe the bus looking for the presence of a device.
Direct configuration is preferred since it can find hardware
regardless of the presence of proper drivers.
.Pp
The autoconfiguration process occurs at system bootstrap and is driven
by a table generated from a
.Do
machine description
.Dc
file by
.Xr config 1 .
For a description of the
.Xr config 1
.Do
device definition
.Dc
language, see
.Xr config 9 .
.Pp
Each device must have a name consisting of an alphanumeric string that
ends with a unit number.
The unit number identifies an instance of the driver.
Device data structures are allocated dynamically during
autoconfiguration, giving a unique address for each instance.
.Pp
Several of the autoconfiguration functions take a strongly-typed variadic
list of arguments to pass information from driver autoconfiguration
functions to the kernel's autoconfiguration system.
This list is constructed using the
.Fn CFARGS
macro, like this example:
.Bd -literal -offset indent
config_search(self, NULL,
    CFARGS(.search = mainbus_search,
           .iattr = "mainbus"));
.Ed
.Pp
Each tag is followed by a tag-specific value.
.Bl -tag -offset indent -width ".Fa devhandle"
.It Fa submatch
A pointer to a
.Sq submatch
function used in
.Em direct
configuration.
.\"
.It Fa search
A pointer to a
.Sq search
function used in
.Em indirect
configuration.
.\"
.It Fa iattr
A pointer to a constant
.Tn C
string
.Pq Vt "const char *"
specifying an interface attribute.
If a parent device carries only a single interface attribute, then this
argument may be omitted.
If an interface attribute is specified that the parent device does not
carry, or no interface attribute is specified and the parent device carries
more than one, behavior is undefined.
On kernels built with the
.Dv DIAGNOSTIC
option, this may result in an assertion panic.
.\"
.It Fa locators
A pointer to a constant array of integers
.Pq Vt "const int *"
containing interface attribute-specific locators.
.\"
.It Fa devhandle
A
.Vt devhandle_t
(passed by value) corresponding to the device being attached.
.El
.Pp
If no arguments are to be passed, the special value
.Dv CFARGS_NONE
may be used in place of the
.Fn CFARGS
macro.
.Sh FUNCTIONS
.Bl -tag -width ".Fn config"
.\"
.\"
.It Fn config_search "parent" "aux" "cfargs"
Cfargs consumed:
.Fa search ,
.Fa iattr ,
.Fa locators .
.\"
.Pp
Performs indirect configuration of physical devices.
.Fn config_search
iterates over all potential children, calling the given
search function
If no search function is specified,
.fn config_search
applies the potential child's match function instead.
The argument
.Fa parent
is the pointer to the parent's device structure.
If an interface attribute is specified, only potential children eligible to
attach to that interface attribute will be consulted.
If specified,
the locators argument lists the locator values for the device and are passed
to the search function.
The given
.Fa aux
argument describes the device that has been found and is simply passed
on through the search function to the child.
.Fn config_search
returns a pointer to the configuration data that indicates the best-matched
child or
.Dv NULL
otherwise.
.Pp
The role of the search function is to call
.Fn config_probe
for each potential child and call
.Fn config_attach
for any positive matches.
If no search function is specified,
then the parent should record the return value from
.Fn config_search
and call
.Fn config_attach
itself.
.Pp
Note that this function is designed so that it can be used to apply an
arbitrary function to all potential children.
In this case callers may choose to ignore the return value.
.\"
.\"
.It Fn config_found "parent" "aux" "print" "cfargs"
Cfargs consumed:
.Fa submatch ,
.Fa iattr ,
.Fa locators ,
.Fa devhandle .
.\"
.Pp
Performs direct configuration on a physical device.
.Fn config_found
is called by the parent and in turn calls the specified submatch function
as determined by the configuration table.
The submatch function compares user-specified locators from the
machine description file against those specifying a found device,
calling
.Fn config_match
if they match
.Pq including wildcard matching .
If a submatch function is not specified, then driver match functions are
called directly.
The argument
.Fa parent
is the pointer to the parent's device structure.
If an interface attribute is specified, only potential children eligible to
attach to that interface attribute will be consulted.
If specified, the locators argument lists the locator values for the found
device and may be used by the submatch function and will be recorded in the
device structure of the child device.
The given
.Fa aux
argument describes the device that has been found.
.Fn config_found
internally uses
.Fn config_search .
The
.Vt softc
structure for the matched device will be allocated, and the
appropriate driver attach function will be called.
If the device is matched, the system prints the name of the child and
parent devices, and then calls the
.Fa print
function to produce additional information if desired.
If no driver takes a match, the same
.Fa print
function is called to complain.
The print function is called with the
.Fa aux
argument and, if the matches failed, the full name (including unit
number) of the parent device, otherwise
.Dv NULL .
The
.Fa print
function must return an integer value.
.Pp
Two special strings,
.Do
not configured
.Dc
and
.Do
unsupported
.Dc
will be appended automatically to non-driver reports if the return
value is
.Dv UNCONF
or
.Dv UNSUPP
respectively; otherwise the function should
return the value
.Dv QUIET .
If a device handle is specified, that handle will be associated with
the resulting child device structure if a driver matches.
.Pp
.Fn config_found
returns a pointer to the attached device's
.Vt device
structure if the device is attached,
.Dv NULL
otherwise.
Most callers can ignore this value, since the system will already have
printed a diagnostic.
.\"
.\"
.It Fn config_match "parent" "cf" "aux"
.\"
Match a device
.Pq direct configuration .
Invokes the driver's match function according to the configuration table.
The
.Fn config_match
function returns a nonzero integer indicating the confidence of
supporting this device and a value of 0 if the driver doesn't support
the device.
.\"
.\"
.It Fn config_probe "parent" "cf" "aux"
.\"
Probe for a device
.Pq indirect configuration .
Invokes the driver's match function according to the configuration table.
The
.Fn config_probe
function returns a nonzero integer to indicate a successful probe
and a value of 0 otherwise.
Unlike
.Fn config_match ,
the return value of
.Fn config_probe
is not intended to reflect a confidence value.
.\"
.\"
.It Fn config_attach "parent" "cf" "aux" "print" "cfargs"
Cfargs consumed:
.Fa locators ,
.Fa devhandle .
.\"
.Pp
Attach a found device.
Allocates the memory for the
.Vt softc
structure and calls the drivers attach function according to the
configuration table.
If successful,
.Fn config_attach
returns a pointer to the
.Vt device
structure.
If unsuccessful, it returns
.Dv NULL .
.\"
.\"
.It Fn config_attach_pseudo "cf"
.\"
Create an instance of a pseudo-device driver.
.Xr config 5
syntax allows the creation of pseudo-devices from which regular
.Ft device_t
instances can be created.
Such objects are similar to the devices that attach at the root of the device
tree.
.Pp
The caller is expected to allocate and fill the
.Ft cfdata_t
object and pass it to
.Fn config_attach_pseudo .
The content of that object is similar to what is returned by
.Fn config_search
for regular devices.
.\"
.\"
.It Fn config_detach "dev" "flags"
.\"
Called by the parent to detach the child device.
The second argument
.Fa flags
contains detachment flags.
Valid values are
.Dv DETACH_FORCE
(force detachment, e.g., because of hardware removal)
and
.Dv DETACH_QUIET
(do not print a notice).
.Fn config_detach
returns zero if successful and an error code otherwise.
.Fn config_detach
is always called from a thread context, allowing condition variables
to be used while the device detaches itself.
.\"
.\"
.It Fn config_detach_children "dev" "flags"
.\"
Iterate through all attached devices, calling
.Fn config_detach
for each child of
.Fa dev ,
passing
.Fa flags .
If detaching any child results in an error, the iteration will halt
and any remaining devices will not be detached.
.Fn config_detach_children
returns zero if successful and an error code otherwise.
.\"
.\"
.It Fn config_deactivate "dev"
.\"
Called by the parent to deactivate the child device
.Fa dev .
.Fn config_deactivate
is called from interrupt context to immediately relinquish resources
and notify dependent kernel subsystems that the device is about to be
detached.
At some later point
.Fn config_detach
will be called to finalise the removal of the device.
.\"
.\"
.It Fn config_defer "dev" "func"
.\"
Called by the child to defer the remainder of its configuration until
all its parent's devices have been attached.
At this point, the function
.Fa func
is called with the argument
.Fa dev .
.\"
.\"
.It Fn config_interrupts "dev" "func"
.\"
Called by the child to defer the remainder of its configuration until
interrupts are enabled.
At this point, the function
.Fa func
is called with the argument
.Fa dev .
.\"
.\"
.It Fn config_mountroot "dev" "func"
.\"
Called by the child to defer the remainder of its configuration until
the root file system is mounted.
At this point, the function
.Fa func
is called with the argument
.Fa dev .
This is used for devices that need to load firmware image from
a mounted file system.
.\"
.\"
.It Fn config_pending_incr
.\"
Increment the
.Va config_pending
semaphore.
It is used to account for deferred configurations before
mounting the root file system.
.\"
.\"
.It Fn config_pending_decr
.\"
Decrement the
.Va config_pending
semaphore.
It is used to account for deferred configurations before
mounting the root file system.
.\"
.\"
.It Fn config_finalize_register "dev" "func"
.\"
.\"
Register a function to be called after all real devices have been found.
.Pp
Registered functions are all executed until all of them return 0.
The callbacks should return 0 to indicate they do not require to be called
another time, but they should be aware that they still might be in case one of
them returns 1.
.El
.Sh CODE REFERENCES
The autoconfiguration framework itself is implemented within the file
.Pa sys/kern/subr_autoconf.c .
Data structures and function prototypes for the framework are located in
.Pa sys/sys/device.h .
.Sh SEE ALSO
.Xr config 1 ,
.Xr config 5 ,
.Xr condvar 9 ,
.Xr config 9 ,
.Xr driver 9
.Sh HISTORY
Autoconfiguration first appeared in
.Bx 4.1 .
The autoconfiguration framework was completely revised in
.Bx 4.4 .
The detach and deactivate interfaces appeared in
.Nx 1.5 .