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-rw-r--r--kernel/Documentation/xtensa/atomctl.txt44
-rw-r--r--kernel/Documentation/xtensa/mmu.txt64
2 files changed, 108 insertions, 0 deletions
diff --git a/kernel/Documentation/xtensa/atomctl.txt b/kernel/Documentation/xtensa/atomctl.txt
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index 000000000..1da783ac2
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+++ b/kernel/Documentation/xtensa/atomctl.txt
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+We Have Atomic Operation Control (ATOMCTL) Register.
+This register determines the effect of using a S32C1I instruction
+with various combinations of:
+
+ 1. With and without an Coherent Cache Controller which
+ can do Atomic Transactions to the memory internally.
+
+ 2. With and without An Intelligent Memory Controller which
+ can do Atomic Transactions itself.
+
+The Core comes up with a default value of for the three types of cache ops:
+
+ 0x28: (WB: Internal, WT: Internal, BY:Exception)
+
+On the FPGA Cards we typically simulate an Intelligent Memory controller
+which can implement RCW transactions. For FPGA cards with an External
+Memory controller we let it to the atomic operations internally while
+doing a Cached (WB) transaction and use the Memory RCW for un-cached
+operations.
+
+For systems without an coherent cache controller, non-MX, we always
+use the memory controllers RCW, thought non-MX controlers likely
+support the Internal Operation.
+
+CUSTOMER-WARNING:
+ Virtually all customers buy their memory controllers from vendors that
+ don't support atomic RCW memory transactions and will likely want to
+ configure this register to not use RCW.
+
+Developers might find using RCW in Bypass mode convenient when testing
+with the cache being bypassed; for example studying cache alias problems.
+
+See Section 4.3.12.4 of ISA; Bits:
+
+ WB WT BY
+ 5 4 | 3 2 | 1 0
+ 2 Bit
+ Field
+ Values WB - Write Back WT - Write Thru BY - Bypass
+--------- --------------- ----------------- ----------------
+ 0 Exception Exception Exception
+ 1 RCW Transaction RCW Transaction RCW Transaction
+ 2 Internal Operation Internal Operation Reserved
+ 3 Reserved Reserved Reserved
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