loader: document the page table setup

          --- old/usr/src/uts/armv6/loader/fakeloader_core.s
          +++ new/usr/src/uts/armv6/loader/fakeloader_core.s

   1    1  /*
   2    2   * This file and its contents are supplied under the terms of the
   3    3   * Common Development and Distribution License ("CDDL"), version 1.0.
   4    4   * You may only use this file in accordance with the terms of version
   5    5   * 1.0 of the CDDL.
   6    6   *
   7    7   * A full copy of the text of the CDDL should have accompanied this
   8    8   * source.  A copy of the CDDL is also available via the Internet at
   9    9   * http://www.illumos.org/license/CDDL.
  10   10   */
  11   11  
  12   12  /*
  13   13   * Copyright 2013 (c) Joyent, Inc. All rights reserved.
  14   14   * Copyright 2015 (c) Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
  15   15   */
  16   16  
  17   17  /*
  18   18   * Every story needs a beginning, this is the loader's.
  19   19   */
  20   20  
  21   21  #include <sys/asm_linkage.h>
  22   22  
  23   23  /*
  24   24   * We put _start into the .text.init section so we can more easily shove it
  25   25   * at the front of the .text.
  26   26   */
  27   27          .section .text.init
  28   28          .align  4
  29   29          .globl  _start
  30   30          .type   _start, %function
  31   31  _start:
  32   32          mov     sp, #0x8000
  33   33          /*
  34   34           * XXX manually fix up the tag start
  35   35           */
  36   36          mov     r2, #0x100
  37   37          bl      fakeload_init
  38   38          SET_SIZE(_start)
  39   39  
  40   40  #if defined(__lint)
  41   41  
  42   42  /* ARGSUSED */
  43   43  void
  44   44  fakeload_unaligned_enable(void)
  45   45  {}
  46   46  
  47   47  #else   /* __lint */
  48   48  
  49   49          /*
  50   50           * Fix up alignment by turning off A and by turning on U.
  51   51           */
  52   52          ENTRY(fakeload_unaligned_enable)
  53   53          mrc     p15, 0, r0, c1, c0, 0
  54   54          orr     r0, #0x400000   /* U = 1 */
  55   55          bic     r0, r0, #2      /* A = 0 */
  56   56          mcr     p15, 0, r0, c1, c0, 0
  57   57          bx      lr
  58   58          SET_SIZE(fakeload_unaligned_enable);
  59   59  
  60   60  #endif  /* __lint */
  61   61  
  62   62  #if defined(__lint)
  63   63  
  64   64  fakeload_pt_setup(uintptr_t ptroot)
  65   65  {}
  66   66  
  67   67  #else /* __lint */

  68   68  
  69   69          /*
  70   70           * We need to set up the world for the first time. We'll do the
  71   71           * following in order:
  72   72           *
  73   73           * o Set the TTBCR to always use TTBR0
  74   74           * o Set domain 0 to manager mode
  75   75           * o Program the Page table root
  76   76           */
  77   77          ENTRY(fakeload_pt_setup)
       78 +        /* use TTBR0 only (should already be true) */
  78   79          mov     r1, #0
  79   80          mcr     p15, 0, r1, c2, c0, 2
       81 +
       82 +        /* set domain 0 to manager mode */
  80   83          mov     r1, #3
  81   84          mcr     p15, 0, r1, c3, c0, 0
  82      -        orr     r0, r0, #0x1b
       85 +
       86 +        /* set TTBR0 to page table root */
       87 +        orr     r0, r0, #0x18           /* Outer WB, no WA Cachable */
       88 +        orr     r0, r0, #0x2            /* Sharable */
       89 +        orr     r0, r0, #0x1            /* Inner Cachable */
  83   90          mcr     p15, 0, r0, c2, c0, 0
  84   91          bx      lr
  85   92          SET_SIZE(fakeload_pt_setup)
  86   93  
  87   94  #endif /* __lint */
  88   95  
  89   96  #if defined(__lint)
  90   97  
  91   98  /* ARGSUSED */
  92   99  void

  93  100  fakeload_mmu_enable(void)
  94  101  {}
  95  102  
  96  103  #else   /* __lint */
  97  104  
  98  105          /*
  99  106           * We first make sure that the ARMv6 pages are enabled (bit 23) and then
 100  107           * enable the MMU (bit 0).
 101  108           */
 102  109          ENTRY(fakeload_mmu_enable)
 103  110          mrc     p15, 0, r0, c1, c0, 0
 104  111          orr     r0, #0x800000           /* enable ARMv6 pages */
 105  112          orr     r0, #0x1                /* enable MMU */
 106  113          mcr     p15, 0, r0, c1, c0, 0
 107  114          bx      lr
 108  115          SET_SIZE(fakeload_mmu_enable)
 109  116  #endif  /* __lint */
 110  117  
 111  118  
 112  119          ENTRY(fakeload_exec)
 113  120          blx     r3
 114  121          /* We should never execute this. If we do we'll go back to a panic */
 115  122          bx      lr
 116  123          SET_SIZE(fakeload_exec)

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