1MTRR_ADD(9)                   Hardware Interfaces                  MTRR_ADD(9)
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NAME

6       mtrr_add - Add a memory type region
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SYNOPSIS

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

13       base
14           Physical base address of region
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16       size
17           Physical size of region
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19       type
20           Type of MTRR desired
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22       increment
23           If this is true do usage counting on the region
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DESCRIPTION

26       Memory type region registers control the caching on newer Intel and non
27       Intel processors. This function allows drivers to request an MTRR is
28       added. The details and hardware specifics of each processor´s
29       implementation are hidden from the caller, but nevertheless the caller
30       should expect to need to provide a power of two size on an equivalent
31       power of two boundary.
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33       If the region cannot be added either because all regions are in use or
34       the CPU cannot support it a negative value is returned. On success the
35       register number for this entry is returned, but should be treated as a
36       cookie only.
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38       On a multiprocessor machine the changes are made to all processors.
39       This is required on x86 by the Intel processors.
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41       The available types are
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43       MTRR_TYPE_UNCACHABLE - No caching
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45       MTRR_TYPE_WRBACK - Write data back in bursts whenever
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47       MTRR_TYPE_WRCOMB - Write data back soon but allow bursts
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49       MTRR_TYPE_WRTHROUGH - Cache reads but not writes
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BUGS

52       Needs a quiet flag for the cases where drivers do not mind failures and
53       do not wish system log messages to be sent.
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56Kernel Hackers Manual 2.6.         June 2019                       MTRR_ADD(9)
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