---
name: "mtrr_add"
section: "9"
platform: "linux"
package: "linux-manual-3.16"
version: "3.16.56-1+deb8u1"
release: "Debian 8 (Jessie)"
platforms: ["linux"]
url: "https://new.carta.tech/mtrr_add"
---

# mtrr\_add(9)

Add a memory type region

## NAME

mtrr\_add - Add a memory type region

## SYNOPSIS

**int mtrr\_add(unsigned long** *base***, unsigned long** *size***, unsigned int** *type***, bool** *increment***);**

## ARGUMENTS

*base*

Physical base address of region

*size*

Physical size of region

*type*

Type of MTRR desired

*increment*

If this is true do usage counting on the region

## DESCRIPTION

Memory type region registers control the caching on newer Intel and non Intel processors. This function allows drivers to request an MTRR is added. The details and hardware specifics of each processor's implementation are hidden from the caller, but nevertheless the caller should expect to need to provide a power of two size on an equivalent power of two boundary.

If the region cannot be added either because all regions are in use or the CPU cannot support it a negative value is returned. On success the register number for this entry is returned, but should be treated as a cookie only.

On a multiprocessor machine the changes are made to all processors. This is required on x86 by the Intel processors.

The available types are

**MTRR\_TYPE\_UNCACHABLE** - No caching

**MTRR\_TYPE\_WRBACK** - Write data back in bursts whenever

**MTRR\_TYPE\_WRCOMB** - Write data back soon but allow bursts

**MTRR\_TYPE\_WRTHROUGH** - Cache reads but not writes

## BUGS

Needs a quiet flag for the cases where drivers do not mind failures and do not wish system log messages to be sent.

## COPYRIGHT