xref: /netbsd/lib/libarch/x86_64/x86_64_get_mtrr.2 (revision c4a72b64) 
1.\"     $NetBSD: x86_64_get_mtrr.2,v 1.3 2002/10/01 16:02:43 wiz Exp $
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37.Dd November 10, 2001
38.Dt X86_64_GET_MTRR 3 x86_64
39.Os
40.Sh NAME
41.Nm x86_64_get_mtrr ,
42.Nm x86_64_set_mtrr
43.Nd access Memory Type Range Registers
44.Sh LIBRARY
45.Lb libx86_64
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 x86_64_get_mtrr "struct mtrr *mtrrp" "int *n"
52.Ft int
53.Fn x86_64_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 on
58.Xr pci 4
59and
60.Xr agp 4
61busses.
62For example, enabling write-combining allows bus-write transfers
63to be combined into a larger transfer before bursting over the bus.
64This can 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.
68The
69.Fa n
70argument is a pointer to an integer containing the number of structures
71pointed to by
72.Fa mtrrp .
73For
74.Fn x86_64_set_mtrr
75the integer pointed to by
76.Fa n
77will be updated to reflect the actual number of MTRRs successfully set.
78For
79.Fn x86_64_get_mtrr
80no more than
81.Fa n
82structures will be copied out, and the integer value pointed to by
83.Fa n
84will be updated to reflect the actual number of valid structures retrieved.
85A
86.Dv NULL
87argument to
88.Fa mtrrp
89will result in just the number of MTRRs available being returned
90in the integer pointed to by
91.Fa n .
92.Pp
93The argument
94.Fa mtrrp
95has the following structure:
96.Bd -literal
97struct mtrr {
98        uint64_t base;
99        uint64_t len;
100        uint8_t type;
101        int flags;
102        pid_t owner;
103};
104.Ed
105.Pp
106The location of the mapping is described by its physical base address
107.Em base
108and length
109.Em len .
110Valid values for
111.Em type
112are:
113.Pp
114.Bl -tag -offset indent -width MTRR_TYPE_UNDEF1 -compact
115.It MTRR_TYPE_UC
116uncached memory
117.It MTRR_TYPE_WC
118use write-combining
119.It MTRR_TYPE_WT
120use write-through caching
121.It MTRR_TYPE_WP
122write-protected memory
123.It MTRR_TYPE_WB
124use write-back caching
125.El
126.Pp
127Valid values for
128.Em flags
129are:
130.Pp
131.Bl -tag -offset indent -width MTRR_PRIVATE -compact
132.It MTRR_PRIVATE
133own range, reset the MTRR when the current process exits
134.It MTRR_FIXED
135use fixed range MTRR
136.It MTRR_VALID
137entry is valid
138.El
139.Pp
140The
141.Em owner
142member the PID of the user process which claims the mapping.
143It is only valid if MTRR_PRIVATE is set in
144.Em flags .
145To clear/reset MTRRs, use a
146.Em flags
147field without MTRR_VALID set.
148.Sh RETURN VALUES
149Upon successful completion zero is returned, otherwise \-1 is returned
150on failure, and the global variable
151.Va errno
152is set to indicate the error.
153The integer value pointed to by
154.Fa n
155will be container the number of successfully processed mtrr structures
156in both cases.
157.Sh ERRORS
158.Bl -tag -width [EINVAL]
159.It Bq Er ENOSYS
160The currently running kernel or CPU has no MTRR support.
161.It Bq Er EINVAL
162The currently running kernel has no MTRR support, or one of the mtrr
163structures pointed to by
164.Fa mtrrp
165is invalid.
166.It Bq Er EBUSY
167No unused MTRRs are available.
168.El
169.Sh HISTORY
170The
171.Fn x86_64_get_mtrr
172and
173.Fn x86_64_set_mtrr
174were derived from their i386 counterparts, which appeared in
175.Nx 1.6 .
176