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@@ -0,0 +1,46 @@
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+MMUv3 initialization sequence.
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+
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+The code in the initialize_mmu macro sets up MMUv3 memory mapping
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+identically to MMUv2 fixed memory mapping. Depending on
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+CONFIG_INITIALIZE_XTENSA_MMU_INSIDE_VMLINUX symbol this code is
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+located in one of the following address ranges:
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+
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+ 0xF0000000..0xFFFFFFFF (will keep same address in MMU v2 layout;
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+ typically ROM)
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+ 0x00000000..0x07FFFFFF (system RAM; this code is actually linked
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+ at 0xD0000000..0xD7FFFFFF [cached]
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+ or 0xD8000000..0xDFFFFFFF [uncached];
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+ in any case, initially runs elsewhere
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+ than linked, so have to be careful)
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+
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+The code has the following assumptions:
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+ This code fragment is run only on an MMU v3.
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+ TLBs are in their reset state.
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+ ITLBCFG and DTLBCFG are zero (reset state).
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+ RASID is 0x04030201 (reset state).
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+ PS.RING is zero (reset state).
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+ LITBASE is zero (reset state, PC-relative literals); required to be PIC.
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+
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+TLB setup proceeds along the following steps.
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+
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+ Legend:
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+ VA = virtual address (two upper nibbles of it);
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+ PA = physical address (two upper nibbles of it);
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+ pc = physical range that contains this code;
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+
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+After step 2, we jump to virtual address in 0x40000000..0x5fffffff
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+that corresponds to next instruction to execute in this code.
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+After step 4, we jump to intended (linked) address of this code.
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+
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+ Step 0 Step1 Step 2 Step3 Step 4 Step5
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+ ============ ===== ============ ===== ============ =====
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+ VA PA PA VA PA PA VA PA PA
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+ ------ -- -- ------ -- -- ------ -- --
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+ E0..FF -> E0 -> E0 E0..FF -> E0 F0..FF -> F0 -> F0
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+ C0..DF -> C0 -> C0 C0..DF -> C0 E0..EF -> F0 -> F0
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+ A0..BF -> A0 -> A0 A0..BF -> A0 D8..DF -> 00 -> 00
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+ 80..9F -> 80 -> 80 80..9F -> 80 D0..D7 -> 00 -> 00
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+ 60..7F -> 60 -> 60 60..7F -> 60
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+ 40..5F -> 40 40..5F -> pc -> pc 40..5F -> pc
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+ 20..3F -> 20 -> 20 20..3F -> 20
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+ 00..1F -> 00 -> 00 00..1F -> 00
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