Man page 9 : mtrr_add

mtrr_add - Add a memory type region

int mtrr_add(unsigned long  base , unsigned long  size , unsigned int  type , bool  increment );

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

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 processorAqs 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

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