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   +------------------+
  86   | Cache aliasing   |  TLBTEMP_BASE_1           0xc8000000  DCACHE_WAY_SIZE
  87   | remap area 1     |
  88   +------------------+
  89   | Cache aliasing   |  TLBTEMP_BASE_2                       DCACHE_WAY_SIZE
  90   | remap area 2     |
  91   +------------------+
  92   +------------------+
  93   | KMAP area        |  PKMAP_BASE                           PTRS_PER_PTE *
  94   |                  |                                       DCACHE_N_COLORS *
  95   |                  |                                       PAGE_SIZE
  96   |                  |                                       (4MB * DCACHE_N_COLORS)
  97   +------------------+
  98   | Atomic KMAP area |  FIXADDR_START                        KM_TYPE_NR *
  99   |                  |                                       NR_CPUS *
 100   |                  |                                       DCACHE_N_COLORS *
 101   |                  |                                       PAGE_SIZE
 102   +------------------+  FIXADDR_TOP              0xcffff000
 103   +------------------+
 104   | Cached KSEG      |  XCHAL_KSEG_CACHED_VADDR  0xd0000000  128MB
 105   +------------------+
 106   | Uncached KSEG    |  XCHAL_KSEG_BYPASS_VADDR  0xd8000000  128MB
 107   +------------------+
 108   | Cached KIO       |  XCHAL_KIO_CACHED_VADDR   0xe0000000  256MB
 109   +------------------+
 110   | Uncached KIO     |  XCHAL_KIO_BYPASS_VADDR   0xf0000000  256MB
 111   +------------------+
 112
 113
 114 256MB cached + 256MB uncached layout::
 115
 116                         Symbol                   VADDR       Size
 117   +------------------+
 118   | Userspace        |                           0x00000000  TASK_SIZE
 119   +------------------+                           0x40000000
 120   +------------------+
 121   | Page table       |  XCHAL_PAGE_TABLE_VADDR   0x80000000  XCHAL_PAGE_TABLE_SIZE
 122   +------------------+
 123   | KASAN shadow map |  KASAN_SHADOW_START       0x80400000  KASAN_SHADOW_SIZE
 124   +------------------+                           0x8e400000
 125   +------------------+
 126   | VMALLOC area     |  VMALLOC_START            0xa0000000  128MB - 64KB
 127   +------------------+  VMALLOC_END
 128   +------------------+
 129   | Cache aliasing   |  TLBTEMP_BASE_1           0xa8000000  DCACHE_WAY_SIZE
 130   | remap area 1     |
 131   +------------------+
 132   | Cache aliasing   |  TLBTEMP_BASE_2                       DCACHE_WAY_SIZE
 133   | remap area 2     |
 134   +------------------+
 135   +------------------+
 136   | KMAP area        |  PKMAP_BASE                           PTRS_PER_PTE *
 137   |                  |                                       DCACHE_N_COLORS *
 138   |                  |                                       PAGE_SIZE
 139   |                  |                                       (4MB * DCACHE_N_COLORS)
 140   +------------------+
 141   | Atomic KMAP area |  FIXADDR_START                        KM_TYPE_NR *
 142   |                  |                                       NR_CPUS *
 143   |                  |                                       DCACHE_N_COLORS *
 144   |                  |                                       PAGE_SIZE
 145   +------------------+  FIXADDR_TOP              0xaffff000
 146   +------------------+
 147   | Cached KSEG      |  XCHAL_KSEG_CACHED_VADDR  0xb0000000  256MB
 148   +------------------+
 149   | Uncached KSEG    |  XCHAL_KSEG_BYPASS_VADDR  0xc0000000  256MB
 150   +------------------+
 151   +------------------+
 152   | Cached KIO       |  XCHAL_KIO_CACHED_VADDR   0xe0000000  256MB
 153   +------------------+
 154   | Uncached KIO     |  XCHAL_KIO_BYPASS_VADDR   0xf0000000  256MB
 155   +------------------+
 156
 157
 158 512MB cached + 512MB uncached layout::
 159
 160                         Symbol                   VADDR       Size
 161   +------------------+
 162   | Userspace        |                           0x00000000  TASK_SIZE
 163   +------------------+                           0x40000000
 164   +------------------+
 165   | Page table       |  XCHAL_PAGE_TABLE_VADDR   0x80000000  XCHAL_PAGE_TABLE_SIZE
 166   +------------------+
 167   | KASAN shadow map |  KASAN_SHADOW_START       0x80400000  KASAN_SHADOW_SIZE
 168   +------------------+                           0x8e400000
 169   +------------------+
 170   | VMALLOC area     |  VMALLOC_START            0x90000000  128MB - 64KB
 171   +------------------+  VMALLOC_END
 172   +------------------+
 173   | Cache aliasing   |  TLBTEMP_BASE_1           0x98000000  DCACHE_WAY_SIZE
 174   | remap area 1     |
 175   +------------------+
 176   | Cache aliasing   |  TLBTEMP_BASE_2                       DCACHE_WAY_SIZE
 177   | remap area 2     |
 178   +------------------+
 179   +------------------+
 180   | KMAP area        |  PKMAP_BASE                           PTRS_PER_PTE *
 181   |                  |                                       DCACHE_N_COLORS *
 182   |                  |                                       PAGE_SIZE
 183   |                  |                                       (4MB * DCACHE_N_COLORS)
 184   +------------------+
 185   | Atomic KMAP area |  FIXADDR_START                        KM_TYPE_NR *
 186   |                  |                                       NR_CPUS *
 187   |                  |                                       DCACHE_N_COLORS *
 188   |                  |                                       PAGE_SIZE
 189   +------------------+  FIXADDR_TOP              0x9ffff000
 190   +------------------+
 191   | Cached KSEG      |  XCHAL_KSEG_CACHED_VADDR  0xa0000000  512MB
 192   +------------------+
 193   | Uncached KSEG    |  XCHAL_KSEG_BYPASS_VADDR  0xc0000000  512MB
 194   +------------------+
 195   | Cached KIO       |  XCHAL_KIO_CACHED_VADDR   0xe0000000  256MB
 196   +------------------+
 197   | Uncached KIO     |  XCHAL_KIO_BYPASS_VADDR   0xf0000000  256MB
 198   +------------------+