docs: move xtensa documentation under Documentation/arch/

Architecture-specific documentation is being moved into Documentation/arch/
as a way of cleaning up the top-level documentation directory and making
the docs hierarchy more closely match the source hierarchy.  Move
Documentation/xtensa into arch/ and fix all in-tree references.

Cc: Chris Zankel <chris@zankel.net>
Reviewed-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

6 files changed, 289 insertions, 1 deletions

diff --git a/Documentation/arch/index.rst b/Documentation/arch/index.rst
index 64a5de81c425..208a8e67599c 100644
--- a/Documentation/arch/index.rst
+++ b/Documentation/arch/index.rst
@@ -25,4 +25,4 @@ implementation.
    ../sh/index
    ../sparc/index
    x86/index
-   ../xtensa/index
+   xtensa/index
diff --git a/Documentation/arch/xtensa/atomctl.rst b/Documentation/arch/xtensa/atomctl.rst
new file mode 100644
index 000000000000..1ecbd0ba9a2e
--- /dev/null
+++ b/Documentation/arch/xtensa/atomctl.rst
@@ -0,0 +1,51 @@
+===========================================
+Atomic Operation Control (ATOMCTL) Register
+===========================================
+
+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/Documentation/arch/xtensa/booting.rst b/Documentation/arch/xtensa/booting.rst
new file mode 100644
index 000000000000..e1b83707e5b6
--- /dev/null
+++ b/Documentation/arch/xtensa/booting.rst
@@ -0,0 +1,22 @@
+=====================================
+Passing boot parameters to the kernel
+=====================================
+
+Boot parameters are represented as a TLV list in the memory. Please see
+arch/xtensa/include/asm/bootparam.h for definition of the bp_tag structure and
+tag value constants. First entry in the list must have type BP_TAG_FIRST, last
+entry must have type BP_TAG_LAST. The address of the first list entry is
+passed to the kernel in the register a2. The address type depends on MMU type:
+
+- For configurations without MMU, with region protection or with MPU the
+  address must be the physical address.
+- For configurations with region translarion MMU or with MMUv3 and CONFIG_MMU=n
+  the address must be a valid address in the current mapping. The kernel will
+  not change the mapping on its own.
+- For configurations with MMUv2 the address must be a virtual address in the
+  default virtual mapping (0xd0000000..0xffffffff).
+- For configurations with MMUv3 and CONFIG_MMU=y the address may be either a
+  virtual or physical address. In either case it must be within the default
+  virtual mapping. It is considered physical if it is within the range of
+  physical addresses covered by the default KSEG mapping (XCHAL_KSEG_PADDR..
+  XCHAL_KSEG_PADDR + XCHAL_KSEG_SIZE), otherwise it is considered virtual.
diff --git a/Documentation/arch/xtensa/features.rst b/Documentation/arch/xtensa/features.rst
new file mode 100644
index 000000000000..6b92c7bfa19d
--- /dev/null
+++ b/Documentation/arch/xtensa/features.rst
@@ -0,0 +1,3 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. kernel-feat:: $srctree/Documentation/features xtensa
diff --git a/Documentation/arch/xtensa/index.rst b/Documentation/arch/xtensa/index.rst
new file mode 100644
index 000000000000..69952446a9be
--- /dev/null
+++ b/Documentation/arch/xtensa/index.rst
@@ -0,0 +1,14 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===================
+Xtensa Architecture
+===================
+
+.. toctree::
+   :maxdepth: 1
+
+   atomctl
+   booting
+   mmu
+
+   features
diff --git a/Documentation/arch/xtensa/mmu.rst b/Documentation/arch/xtensa/mmu.rst
new file mode 100644
index 000000000000..450573afa31a
--- /dev/null
+++ b/Documentation/arch/xtensa/mmu.rst
@@ -0,0 +1,198 @@
+=============================
+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 addresses it was linked for (symbol undefined), or not
+(symbol defined), so it needs to be position-independent.
+
+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 the range 0x40000000..0x5fffffff
+or 0x00000000..0x1fffffff, depending on whether the kernel was loaded below
+0x40000000 or above. That address corresponds to next instruction to execute
+in this code. After step 4, we jump to intended (linked) address of this code.
+The scheme below assumes that the kernel is loaded below 0x40000000.
+
+ ====== =====  =====  =====  =====   ====== =====  =====
+ -      Step0  Step1  Step2  Step3          Step4  Step5
+
+   VA      PA     PA     PA     PA     VA      PA     PA
+ ====== =====  =====  =====  =====   ====== =====  =====
+ E0..FF -> E0  -> E0  -> E0          F0..FF -> F0  -> F0
+ C0..DF -> C0  -> C0  -> C0          E0..EF -> F0  -> F0
+ A0..BF -> A0  -> A0  -> A0          D8..DF -> 00  -> 00
+ 80..9F -> 80  -> 80  -> 80          D0..D7 -> 00  -> 00
+ 60..7F -> 60  -> 60  -> 60
+ 40..5F -> 40         -> pc  -> pc   40..5F -> pc
+ 20..3F -> 20  -> 20  -> 20
+ 00..1F -> 00  -> 00  -> 00
+ ====== =====  =====  =====  =====   ====== =====  =====
+
+The default location of IO peripherals is above 0xf0000000. This may be changed
+using a "ranges" property in a device tree simple-bus node. See the Devicetree
+Specification, section 4.5 for details on the syntax and semantics 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
+
+
+MMUv3 address space layouts.
+============================
+
+Default MMUv2-compatible layout::
+
+                        Symbol                   VADDR       Size
+  +------------------+
+  | Userspace        |                           0x00000000  TASK_SIZE
+  +------------------+                           0x40000000
+  +------------------+
+  | Page table       |  XCHAL_PAGE_TABLE_VADDR   0x80000000  XCHAL_PAGE_TABLE_SIZE
+  +------------------+
+  | KASAN shadow map |  KASAN_SHADOW_START       0x80400000  KASAN_SHADOW_SIZE
+  +------------------+                           0x8e400000
+  +------------------+
+  | VMALLOC area     |  VMALLOC_START            0xc0000000  128MB - 64KB
+  +------------------+  VMALLOC_END
+  +------------------+
+  | Cache aliasing   |  TLBTEMP_BASE_1           0xc8000000  DCACHE_WAY_SIZE
+  | remap area 1     |
+  +------------------+
+  | Cache aliasing   |  TLBTEMP_BASE_2                       DCACHE_WAY_SIZE
+  | remap area 2     |
+  +------------------+
+  +------------------+
+  | KMAP area        |  PKMAP_BASE                           PTRS_PER_PTE *
+  |                  |                                       DCACHE_N_COLORS *
+  |                  |                                       PAGE_SIZE
+  |                  |                                       (4MB * DCACHE_N_COLORS)
+  +------------------+
+  | Atomic KMAP area |  FIXADDR_START                        KM_TYPE_NR *
+  |                  |                                       NR_CPUS *
+  |                  |                                       DCACHE_N_COLORS *
+  |                  |                                       PAGE_SIZE
+  +------------------+  FIXADDR_TOP              0xcffff000
+  +------------------+
+  | Cached KSEG      |  XCHAL_KSEG_CACHED_VADDR  0xd0000000  128MB
+  +------------------+
+  | Uncached KSEG    |  XCHAL_KSEG_BYPASS_VADDR  0xd8000000  128MB
+  +------------------+
+  | Cached KIO       |  XCHAL_KIO_CACHED_VADDR   0xe0000000  256MB
+  +------------------+
+  | Uncached KIO     |  XCHAL_KIO_BYPASS_VADDR   0xf0000000  256MB
+  +------------------+
+
+
+256MB cached + 256MB uncached layout::
+
+                        Symbol                   VADDR       Size
+  +------------------+
+  | Userspace        |                           0x00000000  TASK_SIZE
+  +------------------+                           0x40000000
+  +------------------+
+  | Page table       |  XCHAL_PAGE_TABLE_VADDR   0x80000000  XCHAL_PAGE_TABLE_SIZE
+  +------------------+
+  | KASAN shadow map |  KASAN_SHADOW_START       0x80400000  KASAN_SHADOW_SIZE
+  +------------------+                           0x8e400000
+  +------------------+
+  | VMALLOC area     |  VMALLOC_START            0xa0000000  128MB - 64KB
+  +------------------+  VMALLOC_END
+  +------------------+
+  | Cache aliasing   |  TLBTEMP_BASE_1           0xa8000000  DCACHE_WAY_SIZE
+  | remap area 1     |
+  +------------------+
+  | Cache aliasing   |  TLBTEMP_BASE_2                       DCACHE_WAY_SIZE
+  | remap area 2     |
+  +------------------+
+  +------------------+
+  | KMAP area        |  PKMAP_BASE                           PTRS_PER_PTE *
+  |                  |                                       DCACHE_N_COLORS *
+  |                  |                                       PAGE_SIZE
+  |                  |                                       (4MB * DCACHE_N_COLORS)
+  +------------------+
+  | Atomic KMAP area |  FIXADDR_START                        KM_TYPE_NR *
+  |                  |                                       NR_CPUS *
+  |                  |                                       DCACHE_N_COLORS *
+  |                  |                                       PAGE_SIZE
+  +------------------+  FIXADDR_TOP              0xaffff000
+  +------------------+
+  | Cached KSEG      |  XCHAL_KSEG_CACHED_VADDR  0xb0000000  256MB
+  +------------------+
+  | Uncached KSEG    |  XCHAL_KSEG_BYPASS_VADDR  0xc0000000  256MB
+  +------------------+
+  +------------------+
+  | Cached KIO       |  XCHAL_KIO_CACHED_VADDR   0xe0000000  256MB
+  +------------------+
+  | Uncached KIO     |  XCHAL_KIO_BYPASS_VADDR   0xf0000000  256MB
+  +------------------+
+
+
+512MB cached + 512MB uncached layout::
+
+                        Symbol                   VADDR       Size
+  +------------------+
+  | Userspace        |                           0x00000000  TASK_SIZE
+  +------------------+                           0x40000000
+  +------------------+
+  | Page table       |  XCHAL_PAGE_TABLE_VADDR   0x80000000  XCHAL_PAGE_TABLE_SIZE
+  +------------------+
+  | KASAN shadow map |  KASAN_SHADOW_START       0x80400000  KASAN_SHADOW_SIZE
+  +------------------+                           0x8e400000
+  +------------------+
+  | VMALLOC area     |  VMALLOC_START            0x90000000  128MB - 64KB
+  +------------------+  VMALLOC_END
+  +------------------+
+  | Cache aliasing   |  TLBTEMP_BASE_1           0x98000000  DCACHE_WAY_SIZE
+  | remap area 1     |
+  +------------------+
+  | Cache aliasing   |  TLBTEMP_BASE_2                       DCACHE_WAY_SIZE
+  | remap area 2     |
+  +------------------+
+  +------------------+
+  | KMAP area        |  PKMAP_BASE                           PTRS_PER_PTE *
+  |                  |                                       DCACHE_N_COLORS *
+  |                  |                                       PAGE_SIZE
+  |                  |                                       (4MB * DCACHE_N_COLORS)
+  +------------------+
+  | Atomic KMAP area |  FIXADDR_START                        KM_TYPE_NR *
+  |                  |                                       NR_CPUS *
+  |                  |                                       DCACHE_N_COLORS *
+  |                  |                                       PAGE_SIZE
+  +------------------+  FIXADDR_TOP              0x9ffff000
+  +------------------+
+  | Cached KSEG      |  XCHAL_KSEG_CACHED_VADDR  0xa0000000  512MB
+  +------------------+
+  | Uncached KSEG    |  XCHAL_KSEG_BYPASS_VADDR  0xc0000000  512MB
+  +------------------+
+  | Cached KIO       |  XCHAL_KIO_CACHED_VADDR   0xe0000000  256MB
+  +------------------+
+  | Uncached KIO     |  XCHAL_KIO_BYPASS_VADDR   0xf0000000  256MB
+  +------------------+