375 lines
11 KiB
Groff
375 lines
11 KiB
Groff
.\" $NetBSD: driver.9,v 1.22 2009/05/18 08:58:54 wiz Exp $
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.\"
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.\" Copyright (c) 2001 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Gregory McGarry.
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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 NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd October 14, 2007
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.Dt DRIVER 9
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.Os
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.Sh NAME
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.Nm driver
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.Nd description of a device driver
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/device.h
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.In sys/errno.h
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.Ft static int
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.Fn foo_match "struct device *parent" "struct cfdata *match" "void *aux"
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.Ft static void
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.Fn foo_attach "struct device *parent" "struct device *self" "void *aux"
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.Ft static int
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.Fn foo_detach "struct device *self" "int flags"
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.Ft static int
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.Fn foo_activate "struct device *self" "enum devact act"
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.Sh DESCRIPTION
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This page briefly describes the basic
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.Nx
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autoconfiguration interface used by device drivers.
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For a detailed overview of the autoconfiguration framework see
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.Xr autoconf 9 .
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.Pp
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Each device driver must present to the system a standard
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autoconfiguration interface.
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This interface is provided by the
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.Em cfattach
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structure.
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The interface to the driver is constant and is defined
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statically inside the driver.
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For example, the interface to driver
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.Dq foo
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is defined with:
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.Pp
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.Bd -literal
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CFATTACH_DECL(foo, /* driver name */
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sizeof(struct foo_softc), /* size of instance data */
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foo_match, /* match/probe function */
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foo_attach, /* attach function */
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foo_detach, /* detach function */
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foo_activate); /* activate function */
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.Ed
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.Pp
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For each device instance controlled by the driver, the
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autoconfiguration framework allocates a block of memory to record
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device-instance-specific driver variables.
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The size of this memory block is specified by the second argument in the
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.Em CFATTACH_DECL
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macro.
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The memory block is referred to as the driver's
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.Em softc
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structure.
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The
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.Em softc
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structure is only accessed within the driver, so its definition is
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local to the driver.
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Nevertheless, the
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.Em softc
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structure should adopt the standard
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.Nx
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configuration and naming conventions.
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For example, the
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.Em softc
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structure for driver
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.Dq foo
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is defined with:
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.Pp
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.Bd -literal
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struct foo_softc {
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struct device sc_dev; /* generic device info */
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/* device-specific state */
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};
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.Ed
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.Pp
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The autoconfiguration framework mandates that the first member of the
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.Em softc
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structure must be the driver-independent
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.Em struct device .
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Probably its most useful aspect to the driver is that it contains the
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device-instance name
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.Em dv_xname .
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.Pp
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If a driver has character device interfaces accessed from userland, the driver
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must define the
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.Em cdevsw
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structure.
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The structure is constant and is defined inside the driver.
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For example, the
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.Em cdevsw
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structure for driver
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.Dq foo
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is defined with:
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.Pp
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.Bd -literal
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const struct cdevsw foo_cdevsw {
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int (*d_open)(dev_t, int, int, struct lwp *);
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int (*d_close)(dev_t, int, int, struct lwp *);
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int (*d_read)(dev_t, struct uio *, int);
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int (*d_write)(dev_t, struct uio *, int);
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int (*d_ioctl)(dev_t, u_long, void *, int, struct lwp *);
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void (*d_stop)(struct tty *, int);
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struct tty *(*d_tty)(dev_t);
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int (*d_poll)(dev_t, int, struct lwp *);
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paddr_t (*d_mmap)(dev_t, off_t, int);
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int (*d_kqfilter)(dev_t, struct knote *);
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int d_type;
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};
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.Ed
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.Pp
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The structure variable must be named foo_cdevsw by appending the letters
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.Dq _cdevsw
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to the driver's base name.
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This convention is mandated by the autoconfiguration framework.
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.Pp
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If the driver
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.Dq foo
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has also block device interfaces, the driver must define the
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.Em bdevsw
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structure.
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The structure is constant and is defined inside the driver.
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For example, the
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.Em bdevsw
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structure for driver
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.Dq foo
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is defined with:
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.Pp
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.Bd -literal
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const struct bdevsw foo_bdevsw {
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int (*d_open)(dev_t, int, int, struct lwp *);
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int (*d_close)(dev_t, int, int, struct lwp *);
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void (*d_strategy)(struct buf *);
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int (*d_ioctl)(dev_t, u_long, void *, int, struct lwp *);
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int (*d_dump)(dev_t, daddr_t, void *, size_t);
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int (*d_psize)(dev_t);
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int d_type;
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};
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.Ed
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.Pp
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The structure variable must be named foo_bdevsw by appending the letters
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.Dq _bdevsw
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to the driver's base name.
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This convention is mandated by the autoconfiguration framework.
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.Pp
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During system bootstrap, the autoconfiguration framework searches the
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system for devices.
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For each device driver, its match function is called (via its
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.Em cfattach
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structure) to match the driver with a device instance.
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The match function is called with three arguments.
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This first argument
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.Fa parent
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is a pointer to the driver's parent device structure.
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The second argument
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.Fa match
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is a pointer to a data structure describing the autoconfiguration
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framework's understanding of the driver.
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Both the
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.Fa parent
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and
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.Fa match
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arguments are ignored by most drivers.
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The third argument
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.Fa aux
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contains a pointer to a structure describing a potential
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device-instance.
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It is passed to the driver from the parent.
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The match function would type-cast the
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.Fa aux
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argument to its appropriate attachment structure and use its contents
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to determine whether it supports the device.
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Depending on the device hardware, the contents of the attachment
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structure may contain
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.Dq locators
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to locate the device instance so that the driver can probe it for its
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identity.
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If the probe process identifies additional device properties, it may
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modify the members of the attachment structure.
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For these devices, the
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.Nx
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convention is to
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call the match routine
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.Fn foo_probe
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instead of
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.Fn foo_match
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to make this distinction clear.
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Either way, the match function returns a nonzero integer indicating the
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confidence of supporting this device and a value of 0 if the driver
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doesn't support the device.
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Generally, only a single driver exists for a device, so the match
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function returns 1 for a positive match.
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.Pp
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The autoconfiguration framework will call the attach function
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(via its
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.Em cfattach
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structure)
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of the driver which returns the highest value from its match function.
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The attach function is called with three arguments.
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The attach function performs the necessary process to initialise the
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device for operation.
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The first argument
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.Fa parent
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is a pointer to the driver's parent device structure.
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The second argument
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.Fa self
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is a pointer to the driver's device structure.
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It is also a pointer to our
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.Em softc
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structure since the device structure is its first member.
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The third argument
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.Fa aux
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is a pointer to the attachment structure.
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The
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.Fa parent
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and
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.Fa aux
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arguments are the same as passed to the match function.
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.Pp
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The driver's attach function is called before system interrupts are
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enabled.
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If interrupts are required during initialisation, then the attach
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function should make use of
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.Fn config_interrupts
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(see
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.Xr autoconf 9 ) .
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.Pp
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Some devices can be removed from the system without requiring a system
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reboot.
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The autoconfiguration framework calls the driver's detach function
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(via its
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.Em cfattach
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structure) during device detachment.
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If the device does not support detachment, then the driver does not
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have to provide a detach function.
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The detach function is used to relinquish resources allocated to the
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driver which are no longer needed.
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The first argument
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.Fa self
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is a pointer to the driver's device structure.
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It is the same structure as passed to the attach function.
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The second argument
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.Fa flags
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contains detachment flags.
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Valid values are
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.Dv DETACH_FORCE
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(force detachment; hardware gone) and
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.Dv DETACH_QUIET
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(do not print a notice).
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.Pp
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The autoconfiguration framework may call the driver's activate function
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to notify the driver of a change in the resources that have been
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allocated to it.
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For example, an Ethernet driver has to be notified if the network stack
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is being added or removed from the kernel.
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The first argument to the activate function
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.Fa self
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is a pointer to the driver's device structure.
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It is the same argument as passed to the attach function.
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The second argument
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.Fa act
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describes the action.
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Valid actions are
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.Dv DVACT_ACTIVATE
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(activate the device) and
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.Dv DVACT_DEACTIVATE
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(deactivate the device).
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If the action is not supported the activate function should return
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.Er EOPNOTSUPP .
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The
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.Dv DVACT_DEACTIVATE
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call will only be made if the
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.Dv DVACT_ACTIVATE
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call was successful.
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The activate function is called in interrupt context.
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.Pp
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Most drivers will want to make use of interrupt facilities.
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Interrupt locators provided through the attachment structure should be
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used to establish interrupts within the system.
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Generally, an interrupt interface is provided by the parent.
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The interface will require a handler and a driver-specific argument
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to be specified.
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This argument is usually a pointer to the device-instance-specific
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softc structure.
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When a hardware interrupt for the device occurs the handler is called
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with the argument.
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Interrupt handlers should return 0 for
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.Dq interrupt not for me ,
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1 for
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.Dq I took care of it ,
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or -1 for
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.Do
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I guess it was mine, but I wasn't expecting it
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.Dc .
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.Pp
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For a driver to be compiled into the kernel,
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.Xr config 1
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must be aware of its existence.
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This is done by including an entry in files.\*[Lt]bus\*[Gt] in the
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directory containing the driver.
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For example, the driver
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.Dq foo
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attaching to bus
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.Dq bar
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with dependency on kernel module
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.Dq baz
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has the entry:
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.Bd -literal
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device foo: baz
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attach foo at bar
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file dev/bar/foo.c foo
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.Ed
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.Pp
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An entry can now be added to the machine description file:
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.Bd -literal
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foo* at bar?
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.Ed
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.Pp
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For device interfaces of a driver to be compiled into the kernel,
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.Xr config 1
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must be aware of its existence.
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This is done by including an entry in majors.\*[Lt]arch\*[Gt].
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For example, the driver
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.Dq foo
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with character device interfaces, a character major device number
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.Dq cmaj ,
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block device interfaces, a block device major number
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.Dq bmaj
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and dependency on kernel module
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.Dq baz
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has the entry:
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.Bd -literal
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device-major foo char cmaj block bmaj baz
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.Ed
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.Pp
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For a detailed description of the machine description file and the
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.Dq device definition
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language see
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.Xr config 9 .
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.Sh SEE ALSO
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.Xr config 1 ,
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.Xr autoconf 9 ,
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.Xr config 9 ,
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.Xr powerhook_establish 9 ,
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.Xr shutdownhook_establish 9
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