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Diffstat (limited to 'kernel/Documentation/xtensa/mmu.txt')
| -rw-r--r-- | kernel/Documentation/xtensa/mmu.txt | 64 |
1 files changed, 64 insertions, 0 deletions
diff --git a/kernel/Documentation/xtensa/mmu.txt b/kernel/Documentation/xtensa/mmu.txt new file mode 100644 index 000000000..0312fe664 --- /dev/null +++ b/kernel/Documentation/xtensa/mmu.txt @@ -0,0 +1,64 @@ +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 + +The default location of IO peripherals is above 0xf0000000. This may change +using a "ranges" property in a device tree simple-bus node. See ePAPR 1.1, ยง6.5 +for details on the syntax and semantic of simple-bus nodes. The following +limitations apply: + +1. Only top level simple-bus nodes are considered + +2. Only one (first) simple-bus node is considered + +3. Empty "ranges" properties are not supported + +4. Only the first triplet in the "ranges" property is considered + +5. The parent-bus-address value is rounded down to the nearest 256MB boundary + +6. The IO area covers the entire 256MB segment of parent-bus-address; the + "ranges" triplet length field is ignored |