173 lines
5.1 KiB
Groff
173 lines
5.1 KiB
Groff
.\" $NetBSD: i386_get_mtrr.2,v 1.6 2002/02/20 20:40:48 gmcgarry 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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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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 November 10, 2001
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.Dt I386_GET_MTRR 3 i386
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.Os
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.Sh NAME
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.Nm i386_get_mtrr ,
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.Nm i386_set_mtrr
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.Nd access Memory Type Range Registers
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.Sh LIBRARY
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.Lb libi386
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.Sh SYNOPSIS
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.Fd #include \*[Lt]sys/types.h\*[Gt]
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.Fd #include \*[Lt]machine/sysarch.h\*[Gt]
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.Fd #include \*[Lt]machine/mtrr.h\*[Gt]
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.Ft int
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.Fn i386_get_mtrr "struct mtrr *mtrrp" "int *n"
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.Ft int
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.Fn i386_set_mtrr "struct mtrr *mtrrp" "int *n"
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.Sh DESCRIPTION
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These functions provide an interface to the MTRR registers found on
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686-class processors for controlling processor access to memory ranges.
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This is most useful for accessing devices such as video accelerators
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on
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.Xr pci 4
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and
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.Xr agp 4
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busses. For example, enabling write-combining allows bus-write transfers
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to be combined into a larger transfer before bursting over the bus. This
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can increase performance of write operations 2.5 times or more.
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.Pp
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.Fa mtrrp
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is a pointer to one or more mtrr structures, as described below. The
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.Fa n
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argument is a pointer to an integer containing the number of structures
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pointed to by
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.Fa mtrrp .
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For
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.Fn i386_set_mtrr
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the integer pointed to by
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.Fa n
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will be updated to reflect the actual number of MTRRs successfully set.
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For
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.Fn i386_get_mtrr
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no more than
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.Fa n
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structures will be copied out, and the integer value pointed to by
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.Fa n
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will be updated to reflect the actual number of valid structures
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retrieved.
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A NULL argument to
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.Fa mtrrp
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will result in just the number of MTRRs available being returned
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in the integer pointed to by
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.Fa n .
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.Pp
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The argument
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.Fa mtrrp
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has the following structure:
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.Bd -literal
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struct mtrr {
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uint64_t base;
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uint64_t len;
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uint8_t type;
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int flags;
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pid_t owner;
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};
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.Ed
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.Pp
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The location of the mapping is described by its physical base address
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.Em base
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and length
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.Em len .
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Valid values for
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.Em type
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are:
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.Pp
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.Bl -tag -offset indent -width MTRR_TYPE_UNDEF1 -compact
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.It MTRR_TYPE_UC
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uncached memory
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.It MTRR_TYPE_WC
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use write-combining
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.It MTRR_TYPE_WT
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use write-through caching
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.It MTRR_TYPE_WP
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write-protected memory
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.It MTRR_TYPE_WB
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use write-back caching
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.El
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.Pp
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Valid values for
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.Em flags
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are:
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.Pp
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.Bl -tag -offset indent -width MTRR_PRIVATE -compact
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.It MTRR_PRIVATE
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own range, reset the MTRR when the current process exits
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.It MTRR_FIXED
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use fixed range MTRR
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.It MTRR_VALID
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entry is valid
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.El
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.Pp
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The
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.Em owner
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member the PID of the user process which claims the mapping. It is
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only valid if MTRR_PRIVATE is set in
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.Em flags .
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To clear/reset MTRRs, use a
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.Em flags
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field without MTRR_VALID set.
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.Sh RETURN VALUES
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Upon successful completion zero is returned, otherwise -1 is returned
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on failure, and the global variable
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.Va errno
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is set to indicate the error. The integer value pointed to by
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.Fa n
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will be container the number of successfully processed mtrr structures
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in both cases.
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.Sh ERRORS
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.Bl -tag -width [EINVAL]
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.It Bq Er ENOSYS
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The currently running kernel or CPU has no MTRR support.
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.It Bq Er EINVAL
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The currently running kernel has no MTRR support, or one of the mtrr
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structures pointed to by
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.Fa mtrrp
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is invalid.
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.It Bq Er EBUSY
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No unused MTRRs are available.
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.El
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.Sh HISTORY
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The
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.Fn i386_get_mtrr
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and
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.Fn i386_set_mtrr
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functions appeared in
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.Nx 1.6 .
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