Documentation/xtensa/mmu.rst

   1 =============================
   2 MMUv3 initialization sequence
   3 =============================
   4
   5 The code in the initialize_mmu macro sets up MMUv3 memory mapping
   6 identically to MMUv2 fixed memory mapping. Depending on
   7 CONFIG_INITIALIZE_XTENSA_MMU_INSIDE_VMLINUX symbol this code is
   8 located in addresses it was linked for (symbol undefined), or not
   9 (symbol defined), so it needs to be position-independent.
  10
  11 The code has the following assumptions:
  12
  13   - This code fragment is run only on an MMU v3.
  14   - TLBs are in their reset state.
  15   - ITLBCFG and DTLBCFG are zero (reset state).
  16   - RASID is 0x04030201 (reset state).
  17   - PS.RING is zero (reset state).
  18   - LITBASE is zero (reset state, PC-relative literals); required to be PIC.
  19
  20 TLB setup proceeds along the following steps.
  21
  22   Legend:
  23
  24     - VA = virtual address (two upper nibbles of it);
  25     - PA = physical address (two upper nibbles of it);
  26     - pc = physical range that contains this code;
  27
  28 After step 2, we jump to virtual address in the range 0x40000000..0x5fffffff
  29 or 0x00000000..0x1fffffff, depending on whether the kernel was loaded below
  30 0x40000000 or above. That address corresponds to next instruction to execute
  31 in this code. After step 4, we jump to intended (linked) address of this code.
  32 The scheme below assumes that the kernel is loaded below 0x40000000.
  33
  34  ====== =====  =====  =====  =====   ====== =====  =====
  35  -      Step0  Step1  Step2  Step3          Step4  Step5
  36
  37    VA      PA     PA     PA     PA     VA      PA     PA
  38  ====== =====  =====  =====  =====   ====== =====  =====
  39  E0..FF -> E0  -> E0  -> E0          F0..FF -> F0  -> F0
  40  C0..DF -> C0  -> C0  -> C0          E0..EF -> F0  -> F0
  41  A0..BF -> A0  -> A0  -> A0          D8..DF -> 00  -> 00
  42  80..9F -> 80  -> 80  -> 80          D0..D7 -> 00  -> 00
  43  60..7F -> 60  -> 60  -> 60
  44  40..5F -> 40         -> pc  -> pc   40..5F -> pc
  45  20..3F -> 20  -> 20  -> 20
  46  00..1F -> 00  -> 00  -> 00
  47  ====== =====  =====  =====  =====   ====== =====  =====
  48
  49 The default location of IO peripherals is above 0xf0000000. This may be changed
  50 using a "ranges" property in a device tree simple-bus node. See the Devicetree
  51 Specification, section 4.5 for details on the syntax and semantics of
  52 simple-bus nodes. The following limitations apply:
  53
  54 1. Only top level simple-bus nodes are considered
  55
  56 2. Only one (first) simple-bus node is considered
  57
  58 3. Empty "ranges" properties are not supported
  59
  60 4. Only the first triplet in the "ranges" property is considered
  61
  62 5. The parent-bus-address value is rounded down to the nearest 256MB boundary
  63
  64 6. The IO area covers the entire 256MB segment of parent-bus-address; the
  65    "ranges" triplet length field is ignored
  66
  67
  68 MMUv3 address space layouts.
  69 ============================
  70
  71 Default MMUv2-compatible layout::
  72
  73                         Symbol                   VADDR       Size
  74   +------------------+
  75   | Userspace        |                           0x00000000  TASK_SIZE
  76   +------------------+                           0x40000000
  77   +------------------+
  78   | Page table       |  XCHAL_PAGE_TABLE_VADDR   0x80000000  XCHAL_PAGE_TABLE_SIZE
  79   +------------------+
  80   | KASAN shadow map |  KASAN_SHADOW_START       0x80400000  KASAN_SHADOW_SIZE
  81   +------------------+                           0x8e400000
  82   +------------------+
  83   | VMALLOC area     |  VMALLOC_START            0xc0000000  128MB - 64KB
  84   +------------------+  VMALLOC_END
  85   | Cache aliasing   |  TLBTEMP_BASE_1           0xc7ff0000  DCACHE_WAY_SIZE
  86   | remap area 1     |
  87   +------------------+
  88   | Cache aliasing   |  TLBTEMP_BASE_2                       DCACHE_WAY_SIZE
  89   | remap area 2     |
  90   +------------------+
  91   +------------------+
  92   | KMAP area        |  PKMAP_BASE                           PTRS_PER_PTE *
  93   |                  |                                       DCACHE_N_COLORS *
  94   |                  |                                       PAGE_SIZE
  95   |                  |                                       (4MB * DCACHE_N_COLORS)
  96   +------------------+
  97   | Atomic KMAP area |  FIXADDR_START                        KM_TYPE_NR *
  98   |                  |                                       NR_CPUS *
  99   |                  |                                       DCACHE_N_COLORS *
 100   |                  |                                       PAGE_SIZE
 101   +------------------+  FIXADDR_TOP              0xcffff000
 102   +------------------+
 103   | Cached KSEG      |  XCHAL_KSEG_CACHED_VADDR  0xd0000000  128MB
 104   +------------------+
 105   | Uncached KSEG    |  XCHAL_KSEG_BYPASS_VADDR  0xd8000000  128MB
 106   +------------------+
 107   | Cached KIO       |  XCHAL_KIO_CACHED_VADDR   0xe0000000  256MB
 108   +------------------+
 109   | Uncached KIO     |  XCHAL_KIO_BYPASS_VADDR   0xf0000000  256MB
 110   +------------------+
 111
 112
 113 256MB cached + 256MB uncached layout::
 114
 115                         Symbol                   VADDR       Size
 116   +------------------+
 117   | Userspace        |                           0x00000000  TASK_SIZE
 118   +------------------+                           0x40000000
 119   +------------------+
 120   | Page table       |  XCHAL_PAGE_TABLE_VADDR   0x80000000  XCHAL_PAGE_TABLE_SIZE
 121   +------------------+
 122   | KASAN shadow map |  KASAN_SHADOW_START       0x80400000  KASAN_SHADOW_SIZE
 123   +------------------+                           0x8e400000
 124   +------------------+
 125   | VMALLOC area     |  VMALLOC_START            0xa0000000  128MB - 64KB
 126   +------------------+  VMALLOC_END
 127   | Cache aliasing   |  TLBTEMP_BASE_1           0xa7ff0000  DCACHE_WAY_SIZE
 128   | remap area 1     |
 129   +------------------+
 130   | Cache aliasing   |  TLBTEMP_BASE_2                       DCACHE_WAY_SIZE
 131   | remap area 2     |
 132   +------------------+
 133   +------------------+
 134   | KMAP area        |  PKMAP_BASE                           PTRS_PER_PTE *
 135   |                  |                                       DCACHE_N_COLORS *
 136   |                  |                                       PAGE_SIZE
 137   |                  |                                       (4MB * DCACHE_N_COLORS)
 138   +------------------+
 139   | Atomic KMAP area |  FIXADDR_START                        KM_TYPE_NR *
 140   |                  |                                       NR_CPUS *
 141   |                  |                                       DCACHE_N_COLORS *
 142   |                  |                                       PAGE_SIZE
 143   +------------------+  FIXADDR_TOP              0xaffff000
 144   +------------------+
 145   | Cached KSEG      |  XCHAL_KSEG_CACHED_VADDR  0xb0000000  256MB
 146   +------------------+
 147   | Uncached KSEG    |  XCHAL_KSEG_BYPASS_VADDR  0xc0000000  256MB
 148   +------------------+
 149   +------------------+
 150   | Cached KIO       |  XCHAL_KIO_CACHED_VADDR   0xe0000000  256MB
 151   +------------------+
 152   | Uncached KIO     |  XCHAL_KIO_BYPASS_VADDR   0xf0000000  256MB
 153   +------------------+
 154
 155
 156 512MB cached + 512MB uncached layout::
 157
 158                         Symbol                   VADDR       Size
 159   +------------------+
 160   | Userspace        |                           0x00000000  TASK_SIZE
 161   +------------------+                           0x40000000
 162   +------------------+
 163   | Page table       |  XCHAL_PAGE_TABLE_VADDR   0x80000000  XCHAL_PAGE_TABLE_SIZE
 164   +------------------+
 165   | KASAN shadow map |  KASAN_SHADOW_START       0x80400000  KASAN_SHADOW_SIZE
 166   +------------------+                           0x8e400000
 167   +------------------+
 168   | VMALLOC area     |  VMALLOC_START            0x90000000  128MB - 64KB
 169   +------------------+  VMALLOC_END
 170   | Cache aliasing   |  TLBTEMP_BASE_1           0x97ff0000  DCACHE_WAY_SIZE
 171   | remap area 1     |
 172   +------------------+
 173   | Cache aliasing   |  TLBTEMP_BASE_2                       DCACHE_WAY_SIZE
 174   | remap area 2     |
 175   +------------------+
 176   +------------------+
 177   | KMAP area        |  PKMAP_BASE                           PTRS_PER_PTE *
 178   |                  |                                       DCACHE_N_COLORS *
 179   |                  |                                       PAGE_SIZE
 180   |                  |                                       (4MB * DCACHE_N_COLORS)
 181   +------------------+
 182   | Atomic KMAP area |  FIXADDR_START                        KM_TYPE_NR *
 183   |                  |                                       NR_CPUS *
 184   |                  |                                       DCACHE_N_COLORS *
 185   |                  |                                       PAGE_SIZE
 186   +------------------+  FIXADDR_TOP              0x9ffff000
 187   +------------------+
 188   | Cached KSEG      |  XCHAL_KSEG_CACHED_VADDR  0xa0000000  512MB
 189   +------------------+
 190   | Uncached KSEG    |  XCHAL_KSEG_BYPASS_VADDR  0xc0000000  512MB
 191   +------------------+
 192   | Cached KIO       |  XCHAL_KIO_CACHED_VADDR   0xe0000000  256MB
 193   +------------------+
 194   | Uncached KIO     |  XCHAL_KIO_BYPASS_VADDR   0xf0000000  256MB
 195   +------------------+