1.\" $NetBSD: i386_get_mtrr.2,v 1.6 2002/02/20 20:40:48 gmcgarry Exp $ 2.\" 3.\" Copyright (c) 2001 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Gregory McGarry. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 3. All advertising materials mentioning features or use of this software 18.\" must display the following acknowledgement: 19.\" This product includes software developed by the NetBSD 20.\" Foundation, Inc. and its contributors. 21.\" 4. Neither the name of The NetBSD Foundation nor the names of its 22.\" contributors may be used to endorse or promote products derived 23.\" from this software without specific prior written permission. 24.\" 25.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 26.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 27.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 28.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 29.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 30.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 31.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 32.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 33.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 34.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 35.\" POSSIBILITY OF SUCH DAMAGE. 36.\" 37.Dd November 10, 2001 38.Dt I386_GET_MTRR 3 i386 39.Os 40.Sh NAME 41.Nm i386_get_mtrr , 42.Nm i386_set_mtrr 43.Nd access Memory Type Range Registers 44.Sh LIBRARY 45.Lb libi386 46.Sh SYNOPSIS 47.Fd #include \*[Lt]sys/types.h\*[Gt] 48.Fd #include \*[Lt]machine/sysarch.h\*[Gt] 49.Fd #include \*[Lt]machine/mtrr.h\*[Gt] 50.Ft int 51.Fn i386_get_mtrr "struct mtrr *mtrrp" "int *n" 52.Ft int 53.Fn i386_set_mtrr "struct mtrr *mtrrp" "int *n" 54.Sh DESCRIPTION 55These functions provide an interface to the MTRR registers found on 56686-class processors for controlling processor access to memory ranges. 57This is most useful for accessing devices such as video accelerators 58on 59.Xr pci 4 60and 61.Xr agp 4 62busses. For example, enabling write-combining allows bus-write transfers 63to be combined into a larger transfer before bursting over the bus. This 64can increase performance of write operations 2.5 times or more. 65.Pp 66.Fa mtrrp 67is a pointer to one or more mtrr structures, as described below. The 68.Fa n 69argument is a pointer to an integer containing the number of structures 70pointed to by 71.Fa mtrrp . 72For 73.Fn i386_set_mtrr 74the integer pointed to by 75.Fa n 76will be updated to reflect the actual number of MTRRs successfully set. 77For 78.Fn i386_get_mtrr 79no more than 80.Fa n 81structures will be copied out, and the integer value pointed to by 82.Fa n 83will be updated to reflect the actual number of valid structures 84retrieved. 85A NULL argument to 86.Fa mtrrp 87will result in just the number of MTRRs available being returned 88in the integer pointed to by 89.Fa n . 90.Pp 91The argument 92.Fa mtrrp 93has the following structure: 94.Bd -literal 95struct mtrr { 96 uint64_t base; 97 uint64_t len; 98 uint8_t type; 99 int flags; 100 pid_t owner; 101}; 102.Ed 103.Pp 104The location of the mapping is described by its physical base address 105.Em base 106and length 107.Em len . 108Valid values for 109.Em type 110are: 111.Pp 112.Bl -tag -offset indent -width MTRR_TYPE_UNDEF1 -compact 113.It MTRR_TYPE_UC 114uncached memory 115.It MTRR_TYPE_WC 116use write-combining 117.It MTRR_TYPE_WT 118use write-through caching 119.It MTRR_TYPE_WP 120write-protected memory 121.It MTRR_TYPE_WB 122use write-back caching 123.El 124.Pp 125Valid values for 126.Em flags 127are: 128.Pp 129.Bl -tag -offset indent -width MTRR_PRIVATE -compact 130.It MTRR_PRIVATE 131own range, reset the MTRR when the current process exits 132.It MTRR_FIXED 133use fixed range MTRR 134.It MTRR_VALID 135entry is valid 136.El 137.Pp 138The 139.Em owner 140member the PID of the user process which claims the mapping. It is 141only valid if MTRR_PRIVATE is set in 142.Em flags . 143To clear/reset MTRRs, use a 144.Em flags 145field without MTRR_VALID set. 146.Sh RETURN VALUES 147Upon successful completion zero is returned, otherwise -1 is returned 148on failure, and the global variable 149.Va errno 150is set to indicate the error. The integer value pointed to by 151.Fa n 152will be container the number of successfully processed mtrr structures 153in both cases. 154.Sh ERRORS 155.Bl -tag -width [EINVAL] 156.It Bq Er ENOSYS 157The currently running kernel or CPU has no MTRR support. 158.It Bq Er EINVAL 159The currently running kernel has no MTRR support, or one of the mtrr 160structures pointed to by 161.Fa mtrrp 162is invalid. 163.It Bq Er EBUSY 164No unused MTRRs are available. 165.El 166.Sh HISTORY 167The 168.Fn i386_get_mtrr 169and 170.Fn i386_set_mtrr 171functions appeared in 172.Nx 1.6 . 173