65 lines
2.6 KiB
Plaintext
65 lines
2.6 KiB
Plaintext
MMUv3 initialization sequence.
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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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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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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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TLB setup proceeds along the following steps.
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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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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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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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The default location of IO peripherals is above 0xf0000000. This may change
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using a "ranges" property in a device tree simple-bus node. See ePAPR 1.1, §6.5
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for details on the syntax and semantic of simple-bus nodes. The following
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limitations apply:
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1. Only top level simple-bus nodes are considered
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2. Only one (first) simple-bus node is considered
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3. Empty "ranges" properties are not supported
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4. Only the first triplet in the "ranges" property is considered
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5. The parent-bus-address value is rounded down to the nearest 256MB boundary
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6. The IO area covers the entire 256MB segment of parent-bus-address; the
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"ranges" triplet length field is ignored
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