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authorMax Filippov <jcmvbkbc@gmail.com>2013-03-04 23:48:14 +0400
committerChris Zankel <chris@zankel.net>2013-05-09 01:07:09 -0700
commit93e294ac99cc005044ab6357a26998eb962a10e8 (patch)
tree6bef6301d1e442c0713003ff2889e9469b71a69f /Documentation
parente85e335f8ff615f74e29e09cc2599f095600114b (diff)
downloadlinux-linaro-stable-93e294ac99cc005044ab6357a26998eb962a10e8.tar.gz
xtensa: document MMUv3 setup sequence
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com> Signed-off-by: Chris Zankel <chris@zankel.net>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/xtensa/mmu.txt46
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diff --git a/Documentation/xtensa/mmu.txt b/Documentation/xtensa/mmu.txt
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+MMUv3 initialization sequence.
+
+The code in the initialize_mmu macro sets up MMUv3 memory mapping
+identically to MMUv2 fixed memory mapping. Depending on
+CONFIG_INITIALIZE_XTENSA_MMU_INSIDE_VMLINUX symbol this code is
+located in one of the following address ranges:
+
+ 0xF0000000..0xFFFFFFFF (will keep same address in MMU v2 layout;
+ typically ROM)
+ 0x00000000..0x07FFFFFF (system RAM; this code is actually linked
+ at 0xD0000000..0xD7FFFFFF [cached]
+ or 0xD8000000..0xDFFFFFFF [uncached];
+ in any case, initially runs elsewhere
+ than linked, so have to be careful)
+
+The code has the following assumptions:
+ This code fragment is run only on an MMU v3.
+ TLBs are in their reset state.
+ ITLBCFG and DTLBCFG are zero (reset state).
+ RASID is 0x04030201 (reset state).
+ PS.RING is zero (reset state).
+ LITBASE is zero (reset state, PC-relative literals); required to be PIC.
+
+TLB setup proceeds along the following steps.
+
+ Legend:
+ VA = virtual address (two upper nibbles of it);
+ PA = physical address (two upper nibbles of it);
+ pc = physical range that contains this code;
+
+After step 2, we jump to virtual address in 0x40000000..0x5fffffff
+that corresponds to next instruction to execute in this code.
+After step 4, we jump to intended (linked) address of this code.
+
+ Step 0 Step1 Step 2 Step3 Step 4 Step5
+ ============ ===== ============ ===== ============ =====
+ VA PA PA VA PA PA VA PA PA
+ ------ -- -- ------ -- -- ------ -- --
+ E0..FF -> E0 -> E0 E0..FF -> E0 F0..FF -> F0 -> F0
+ C0..DF -> C0 -> C0 C0..DF -> C0 E0..EF -> F0 -> F0
+ A0..BF -> A0 -> A0 A0..BF -> A0 D8..DF -> 00 -> 00
+ 80..9F -> 80 -> 80 80..9F -> 80 D0..D7 -> 00 -> 00
+ 60..7F -> 60 -> 60 60..7F -> 60
+ 40..5F -> 40 40..5F -> pc -> pc 40..5F -> pc
+ 20..3F -> 20 -> 20 20..3F -> 20
+ 00..1F -> 00 -> 00 00..1F -> 00