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| author | Alex Shi <alex.shi@linaro.org> | 2016-08-18 12:33:31 +0800 |
|---|---|---|
| committer | Alex Shi <alex.shi@linaro.org> | 2016-08-18 12:33:31 +0800 |
| commit | fdd85431d91c9da37e9e696eb8fe80f1a2dcdbeb (patch) | |
| tree | ac60b28ebed345df274ce42aa3c9f3ee091875d1 /Documentation | |
| parent | e01035c1a71d7cceebc3df92f79577df7438523a (diff) | |
| parent | e779279da78339ec75fa72571ef901a447762cc6 (diff) | |
Merge branch 'linux-linaro-lsk-v4.4' into linux-linaro-lsk-v4.4-android
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/x86/pat.txt | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/Documentation/x86/pat.txt b/Documentation/x86/pat.txt index 54944c71b819..2a4ee6302122 100644 --- a/Documentation/x86/pat.txt +++ b/Documentation/x86/pat.txt @@ -196,3 +196,35 @@ Another, more verbose way of getting PAT related debug messages is with "debugpat" boot parameter. With this parameter, various debug messages are printed to dmesg log. +PAT Initialization +------------------ + +The following table describes how PAT is initialized under various +configurations. The PAT MSR must be updated by Linux in order to support WC +and WT attributes. Otherwise, the PAT MSR has the value programmed in it +by the firmware. Note, Xen enables WC attribute in the PAT MSR for guests. + + MTRR PAT Call Sequence PAT State PAT MSR + ========================================================= + E E MTRR -> PAT init Enabled OS + E D MTRR -> PAT init Disabled - + D E MTRR -> PAT disable Disabled BIOS + D D MTRR -> PAT disable Disabled - + - np/E PAT -> PAT disable Disabled BIOS + - np/D PAT -> PAT disable Disabled - + E !P/E MTRR -> PAT init Disabled BIOS + D !P/E MTRR -> PAT disable Disabled BIOS + !M !P/E MTRR stub -> PAT disable Disabled BIOS + + Legend + ------------------------------------------------ + E Feature enabled in CPU + D Feature disabled/unsupported in CPU + np "nopat" boot option specified + !P CONFIG_X86_PAT option unset + !M CONFIG_MTRR option unset + Enabled PAT state set to enabled + Disabled PAT state set to disabled + OS PAT initializes PAT MSR with OS setting + BIOS PAT keeps PAT MSR with BIOS setting + |