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.\" $NetBSD: amd64_get_mtrr.2,v 1.6 2002/02/20 20:40:48 gmcgarry Exp $
.\"
.\" Copyright (c) 2001 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Gregory McGarry.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the NetBSD
.\" Foundation, Inc. and its contributors.
.\" 4. Neither the name of The NetBSD Foundation nor the names of its
.\" contributors may be used to endorse or promote products derived
.\" from this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd November 10, 2001
.Dt AMD64_GET_MTRR 3 amd64
.Os
.Sh NAME
.Nm amd64_get_mtrr ,
.Nm amd64_set_mtrr
.Nd access Memory Type Range Registers
.Sh SYNOPSIS
.Fd #include \*[Lt]sys/types.h\*[Gt]
.Fd #include \*[Lt]machine/sysarch.h\*[Gt]
.Fd #include \*[Lt]machine/mtrr.h\*[Gt]
.Ft int
.Fn amd64_get_mtrr "struct mtrr *mtrrp" "int *n"
.Ft int
.Fn amd64_set_mtrr "struct mtrr *mtrrp" "int *n"
.Sh DESCRIPTION
These functions provide an interface to the MTRR registers found on
686-class processors for controlling processor access to memory ranges.
This is most useful for accessing devices such as video accelerators
on
.Xr pci 4
and
.Xr agp 4
busses. For example, enabling write-combining allows bus-write transfers
to be combined into a larger transfer before bursting over the bus. This
can increase performance of write operations 2.5 times or more.
.Pp
.Fa mtrrp
is a pointer to one or more mtrr structures, as described below. The
.Fa n
argument is a pointer to an integer containing the number of structures
pointed to by
.Fa mtrrp .
For
.Fn amd64_set_mtrr
the integer pointed to by
.Fa n
will be updated to reflect the actual number of MTRRs successfully set.
For
.Fn amd64_get_mtrr
no more than
.Fa n
structures will be copied out, and the integer value pointed to by
.Fa n
will be updated to reflect the actual number of valid structures
retrieved.
A NULL argument to
.Fa mtrrp
will result in just the number of MTRRs available being returned
in the integer pointed to by
.Fa n .
.Pp
The argument
.Fa mtrrp
has the following structure:
.Bd -literal
struct mtrr {
uint64_t base;
uint64_t len;
uint8_t type;
int flags;
pid_t owner;
};
.Ed
.Pp
The location of the mapping is described by its physical base address
.Em base
and length
.Em len .
Valid values for
.Em type
are:
.Pp
.Bl -tag -offset indent -width MTRR_TYPE_UNDEF1 -compact
.It MTRR_TYPE_UC
uncached memory
.It MTRR_TYPE_WC
use write-combining
.It MTRR_TYPE_WT
use write-through caching
.It MTRR_TYPE_WP
write-protected memory
.It MTRR_TYPE_WB
use write-back caching
.El
.Pp
Valid values for
.Em flags
are:
.Pp
.Bl -tag -offset indent -width MTRR_PRIVATE -compact
.It MTRR_PRIVATE
own range, reset the MTRR when the current process exits
.It MTRR_FIXED
use fixed range MTRR
.It MTRR_VALID
entry is valid
.El
.Pp
The
.Em owner
member the PID of the user process which claims the mapping. It is
only valid if MTRR_PRIVATE is set in
.Em flags .
To clear/reset MTRRs, use a
.Em flags
field without MTRR_VALID set.
.Sh RETURN VALUES
Upon successful completion zero is returned, otherwise -1 is returned
on failure, and the global variable
.Va errno
is set to indicate the error. The integer value pointed to by
.Fa n
will be container the number of successfully processed mtrr structures
in both cases.
.Sh ERRORS
.Bl -tag -width [EINVAL]
.It Bq Er ENOSYS
The currently running kernel or CPU has no MTRR support.
.It Bq Er EINVAL
The currently running kernel has no MTRR support, or one of the mtrr
structures pointed to by
.Fa mtrrp
is invalid.
.It Bq Er EBUSY
No unused MTRRs are available.
.El
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