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asltree.c revision 1.12
      1 /******************************************************************************
      2  *
      3  * Module Name: asltree - Parse tree management
      4  *
      5  *****************************************************************************/
      6 
      7 /*
      8  * Copyright (C) 2000 - 2018, Intel Corp.
      9  * All rights reserved.
     10  *
     11  * Redistribution and use in source and binary forms, with or without
     12  * modification, are permitted provided that the following conditions
     13  * are met:
     14  * 1. Redistributions of source code must retain the above copyright
     15  *    notice, this list of conditions, and the following disclaimer,
     16  *    without modification.
     17  * 2. Redistributions in binary form must reproduce at minimum a disclaimer
     18  *    substantially similar to the "NO WARRANTY" disclaimer below
     19  *    ("Disclaimer") and any redistribution must be conditioned upon
     20  *    including a substantially similar Disclaimer requirement for further
     21  *    binary redistribution.
     22  * 3. Neither the names of the above-listed copyright holders nor the names
     23  *    of any contributors may be used to endorse or promote products derived
     24  *    from this software without specific prior written permission.
     25  *
     26  * Alternatively, this software may be distributed under the terms of the
     27  * GNU General Public License ("GPL") version 2 as published by the Free
     28  * Software Foundation.
     29  *
     30  * NO WARRANTY
     31  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     32  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     33  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR
     34  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
     35  * HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     36  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     37  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     38  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
     39  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
     40  * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     41  * POSSIBILITY OF SUCH DAMAGES.
     42  */
     43 
     44 #include "aslcompiler.h"
     45 #include "aslcompiler.y.h"
     46 #include "acapps.h"
     47 
     48 #define _COMPONENT          ACPI_COMPILER
     49         ACPI_MODULE_NAME    ("asltree")
     50 
     51 
     52 /*******************************************************************************
     53  *
     54  * FUNCTION:    TrSetOpIntegerValue
     55  *
     56  * PARAMETERS:  ParseOpcode         - New opcode to be assigned to the op
     57  *              Op                  - An existing parse op
     58  *
     59  * RETURN:      The updated op
     60  *
     61  * DESCRIPTION: Used to set the integer value of a op,
     62  *              usually to a specific size (8, 16, 32, or 64 bits)
     63  *
     64  ******************************************************************************/
     65 
     66 ACPI_PARSE_OBJECT *
     67 TrSetOpIntegerValue (
     68     UINT32                  ParseOpcode,
     69     ACPI_PARSE_OBJECT       *Op)
     70 {
     71 
     72     if (!Op)
     73     {
     74         return (NULL);
     75     }
     76 
     77     DbgPrint (ASL_PARSE_OUTPUT,
     78         "\nUpdateOp: Old - %s, New - %s\n",
     79         UtGetOpName (Op->Asl.ParseOpcode),
     80         UtGetOpName (ParseOpcode));
     81 
     82     /* Assign new opcode and name */
     83 
     84     if (Op->Asl.ParseOpcode == PARSEOP_ONES)
     85     {
     86         switch (ParseOpcode)
     87         {
     88         case PARSEOP_BYTECONST:
     89 
     90             Op->Asl.Value.Integer = ACPI_UINT8_MAX;
     91             break;
     92 
     93         case PARSEOP_WORDCONST:
     94 
     95             Op->Asl.Value.Integer = ACPI_UINT16_MAX;
     96             break;
     97 
     98         case PARSEOP_DWORDCONST:
     99 
    100             Op->Asl.Value.Integer = ACPI_UINT32_MAX;
    101             break;
    102 
    103         /* Don't need to do the QWORD case */
    104 
    105         default:
    106 
    107             /* Don't care about others */
    108             break;
    109         }
    110     }
    111 
    112     Op->Asl.ParseOpcode = (UINT16) ParseOpcode;
    113     UtSetParseOpName (Op);
    114 
    115     /*
    116      * For the BYTE, WORD, and DWORD constants, make sure that the integer
    117      * that was passed in will actually fit into the data type
    118      */
    119     switch (ParseOpcode)
    120     {
    121     case PARSEOP_BYTECONST:
    122 
    123         UtCheckIntegerRange (Op, 0x00, ACPI_UINT8_MAX);
    124         Op->Asl.Value.Integer &= ACPI_UINT8_MAX;
    125         break;
    126 
    127     case PARSEOP_WORDCONST:
    128 
    129         UtCheckIntegerRange (Op, 0x00, ACPI_UINT16_MAX);
    130         Op->Asl.Value.Integer &= ACPI_UINT16_MAX;
    131         break;
    132 
    133     case PARSEOP_DWORDCONST:
    134 
    135         UtCheckIntegerRange (Op, 0x00, ACPI_UINT32_MAX);
    136         Op->Asl.Value.Integer &= ACPI_UINT32_MAX;
    137         break;
    138 
    139     default:
    140 
    141         /* Don't care about others, don't need to check QWORD */
    142 
    143         break;
    144     }
    145 
    146     /* Converter: if this is a method invocation, turn off capture comments */
    147 
    148     if (AcpiGbl_CaptureComments &&
    149         (ParseOpcode == PARSEOP_METHODCALL))
    150     {
    151         Gbl_CommentState.CaptureComments = FALSE;
    152     }
    153 
    154     return (Op);
    155 }
    156 
    157 
    158 /*******************************************************************************
    159  *
    160  * FUNCTION:    TrSetOpFlags
    161  *
    162  * PARAMETERS:  Op                  - An existing parse op
    163  *              Flags               - New flags word
    164  *
    165  * RETURN:      The updated parser op
    166  *
    167  * DESCRIPTION: Set bits in the op flags word. Will not clear bits, only set
    168  *
    169  ******************************************************************************/
    170 
    171 ACPI_PARSE_OBJECT *
    172 TrSetOpFlags (
    173     ACPI_PARSE_OBJECT       *Op,
    174     UINT32                  Flags)
    175 {
    176 
    177     if (!Op)
    178     {
    179         return (NULL);
    180     }
    181 
    182     DbgPrint (ASL_PARSE_OUTPUT,
    183         "\nSetOpFlags: %s Op %p, %8.8X", Op->Asl.ParseOpName, Op, Flags);
    184 
    185     TrPrintOpFlags (Flags, ASL_PARSE_OUTPUT);
    186     DbgPrint (ASL_PARSE_OUTPUT, "\n\n");
    187 
    188     Op->Asl.CompileFlags |= Flags;
    189     return (Op);
    190 }
    191 
    192 
    193 /*******************************************************************************
    194  *
    195  * FUNCTION:    TrSetOpAmlLength
    196  *
    197  * PARAMETERS:  Op                  - An existing parse op
    198  *              Length              - AML Length
    199  *
    200  * RETURN:      The updated parser op
    201  *
    202  * DESCRIPTION: Set the AML Length in a op. Used by the parser to indicate
    203  *              the presence of a op that must be reduced to a fixed length
    204  *              constant.
    205  *
    206  ******************************************************************************/
    207 
    208 ACPI_PARSE_OBJECT *
    209 TrSetOpAmlLength (
    210     ACPI_PARSE_OBJECT       *Op,
    211     UINT32                  Length)
    212 {
    213 
    214     DbgPrint (ASL_PARSE_OUTPUT,
    215         "\nSetOpAmlLength: Op %p, %8.8X\n", Op, Length);
    216 
    217     if (!Op)
    218     {
    219         return (NULL);
    220     }
    221 
    222     Op->Asl.AmlLength = Length;
    223     return (Op);
    224 }
    225 
    226 
    227 /*******************************************************************************
    228  *
    229  * FUNCTION:    TrSetOpParent
    230  *
    231  * PARAMETERS:  Op                  - To be set to new parent
    232  *              ParentOp            - The parent
    233  *
    234  * RETURN:      None, sets Op parent directly
    235  *
    236  * DESCRIPTION: Change the parent of a parse op.
    237  *
    238  ******************************************************************************/
    239 
    240 void
    241 TrSetOpParent (
    242     ACPI_PARSE_OBJECT       *Op,
    243     ACPI_PARSE_OBJECT       *ParentOp)
    244 {
    245 
    246     Op->Asl.Parent = ParentOp;
    247 }
    248 
    249 
    250 /*******************************************************************************
    251  *
    252  * FUNCTION:    TrSetOpCurrentFilename
    253  *
    254  * PARAMETERS:  Op                  - An existing parse op
    255  *
    256  * RETURN:      None
    257  *
    258  * DESCRIPTION: Save the include file filename. Used for debug output only.
    259  *
    260  ******************************************************************************/
    261 
    262 void
    263 TrSetOpCurrentFilename (
    264     ACPI_PARSE_OBJECT       *Op)
    265 {
    266 
    267     Op->Asl.Filename = Gbl_PreviousIncludeFilename;
    268 }
    269 
    270 
    271 /*******************************************************************************
    272  *
    273  * FUNCTION:    TrSetOpIntegerWidth
    274  *
    275  * PARAMETERS:  Op                  - An existing parse op
    276  *
    277  * RETURN:      None
    278  *
    279  * DESCRIPTION:
    280  *
    281  ******************************************************************************/
    282 
    283 void
    284 TrSetOpIntegerWidth (
    285     ACPI_PARSE_OBJECT       *TableSignatureOp,
    286     ACPI_PARSE_OBJECT       *RevisionOp)
    287 {
    288 
    289     /* TBD: Check table sig? (DSDT vs. SSDT) */
    290 
    291     /* Handle command-line version override */
    292 
    293     if (Gbl_RevisionOverride)
    294     {
    295         AcpiUtSetIntegerWidth (Gbl_RevisionOverride);
    296     }
    297     else
    298     {
    299         AcpiUtSetIntegerWidth ((UINT8) RevisionOp->Asl.Value.Integer);
    300     }
    301 }
    302 
    303 
    304 /*******************************************************************************
    305  *
    306  * FUNCTION:    TrSetOpEndLineNumber
    307  *
    308  * PARAMETERS:  Op                - An existing parse op
    309  *
    310  * RETURN:      None.
    311  *
    312  * DESCRIPTION: Set the ending line numbers (file line and logical line) of a
    313  *              parse op to the current line numbers.
    314  *
    315  ******************************************************************************/
    316 
    317 void
    318 TrSetOpEndLineNumber (
    319     ACPI_PARSE_OBJECT       *Op)
    320 {
    321 
    322     /* If the end line # is already set, just return */
    323 
    324     if (Op->Asl.EndLine)
    325     {
    326         return;
    327     }
    328 
    329     Op->Asl.EndLine = Gbl_CurrentLineNumber;
    330     Op->Asl.EndLogicalLine = Gbl_LogicalLineNumber;
    331 }
    332 
    333 
    334 /*******************************************************************************
    335  *
    336  * FUNCTION:    TrLinkOpChildren
    337  *
    338  * PARAMETERS:  Op                - An existing parse op
    339  *              NumChildren        - Number of children to follow
    340  *              ...                - A list of child ops to link to the new
    341  *                                   op. NumChildren long.
    342  *
    343  * RETURN:      The updated (linked) op
    344  *
    345  * DESCRIPTION: Link a group of ops to an existing parse op
    346  *
    347  ******************************************************************************/
    348 
    349 ACPI_PARSE_OBJECT *
    350 TrLinkOpChildren (
    351     ACPI_PARSE_OBJECT       *Op,
    352     UINT32                  NumChildren,
    353     ...)
    354 {
    355     ACPI_PARSE_OBJECT       *Child;
    356     ACPI_PARSE_OBJECT       *PrevChild;
    357     va_list                 ap;
    358     UINT32                  i;
    359     BOOLEAN                 FirstChild;
    360 
    361 
    362     va_start (ap, NumChildren);
    363 
    364     TrSetOpEndLineNumber (Op);
    365 
    366     DbgPrint (ASL_PARSE_OUTPUT,
    367         "\nLinkChildren  Line [%u to %u] NewParent %p Child %u Op %s  ",
    368         Op->Asl.LineNumber, Op->Asl.EndLine,
    369         Op, NumChildren, UtGetOpName(Op->Asl.ParseOpcode));
    370 
    371     switch (Op->Asl.ParseOpcode)
    372     {
    373     case PARSEOP_ASL_CODE:
    374 
    375         Gbl_ParseTreeRoot = Op;
    376         Op->Asl.ParseOpcode = PARSEOP_DEFAULT_ARG;
    377         DbgPrint (ASL_PARSE_OUTPUT, "ASLCODE (Tree Completed)->");
    378         break;
    379 
    380     case PARSEOP_DEFINITION_BLOCK:
    381 
    382         DbgPrint (ASL_PARSE_OUTPUT, "DEFINITION_BLOCK (Tree Completed)->");
    383         break;
    384 
    385     case PARSEOP_OPERATIONREGION:
    386 
    387         DbgPrint (ASL_PARSE_OUTPUT, "OPREGION->");
    388         break;
    389 
    390     case PARSEOP_OR:
    391 
    392         DbgPrint (ASL_PARSE_OUTPUT, "OR->");
    393         break;
    394 
    395     default:
    396 
    397         /* Nothing to do for other opcodes */
    398 
    399         break;
    400     }
    401 
    402     /* The following is for capturing comments */
    403 
    404     if (AcpiGbl_CaptureComments)
    405     {
    406         /*
    407          * If there are "regular comments" detected at this point,
    408          * then is an endBlk comment. Categorize it as so and distribute
    409          * all regular comments to this parse op.
    410          */
    411         if (Gbl_CommentListHead)
    412         {
    413             Op->Asl.EndBlkComment = Gbl_CommentListHead;
    414             CvDbgPrint ("EndBlk Comment for %s: %s",
    415                 Op->Asl.ParseOpName, Gbl_CommentListHead->Comment);
    416             Gbl_CommentListHead = NULL;
    417             Gbl_CommentListTail = NULL;
    418         }
    419     }
    420 
    421     /* Link the new op to it's children */
    422 
    423     PrevChild = NULL;
    424     FirstChild = TRUE;
    425     for (i = 0; i < NumChildren; i++)
    426     {
    427         Child = va_arg (ap, ACPI_PARSE_OBJECT *);
    428 
    429         if ((Child == PrevChild) && (Child != NULL))
    430         {
    431             AslError (ASL_WARNING, ASL_MSG_COMPILER_INTERNAL, Child,
    432                 "Child op list invalid");
    433             va_end(ap);
    434             return (Op);
    435         }
    436 
    437         DbgPrint (ASL_PARSE_OUTPUT, "%p, ", Child);
    438 
    439         /*
    440          * If child is NULL, this means that an optional argument
    441          * was omitted. We must create a placeholder with a special
    442          * opcode (DEFAULT_ARG) so that the code generator will know
    443          * that it must emit the correct default for this argument
    444          */
    445         if (!Child)
    446         {
    447             Child = TrAllocateOp (PARSEOP_DEFAULT_ARG);
    448         }
    449 
    450         /* Link first child to parent */
    451 
    452         if (FirstChild)
    453         {
    454             FirstChild = FALSE;
    455             Op->Asl.Child = Child;
    456         }
    457 
    458         /* Point all children to parent */
    459 
    460         Child->Asl.Parent = Op;
    461 
    462         /* Link children in a peer list */
    463 
    464         if (PrevChild)
    465         {
    466             PrevChild->Asl.Next = Child;
    467         }
    468 
    469         /*
    470          * This child might be a list, point all ops in the list
    471          * to the same parent
    472          */
    473         while (Child->Asl.Next)
    474         {
    475             Child = Child->Asl.Next;
    476             Child->Asl.Parent = Op;
    477         }
    478 
    479         PrevChild = Child;
    480     }
    481 
    482     va_end(ap);
    483     DbgPrint (ASL_PARSE_OUTPUT, "\n\n");
    484 
    485     if (AcpiGbl_CaptureComments)
    486     {
    487         Gbl_CommentState.LatestParseOp = Op;
    488         CvDbgPrint ("TrLinkOpChildren=====Set latest parse op to this op.\n");
    489     }
    490 
    491     return (Op);
    492 }
    493 
    494 
    495 /*******************************************************************************
    496  *
    497  * FUNCTION:    TrLinkPeerOp
    498  *
    499  * PARAMETERS:  Op1           - First peer
    500  *              Op2           - Second peer
    501  *
    502  * RETURN:      Op1 or the non-null op.
    503  *
    504  * DESCRIPTION: Link two ops as peers. Handles cases where one peer is null.
    505  *
    506  ******************************************************************************/
    507 
    508 ACPI_PARSE_OBJECT *
    509 TrLinkPeerOp (
    510     ACPI_PARSE_OBJECT       *Op1,
    511     ACPI_PARSE_OBJECT       *Op2)
    512 {
    513     ACPI_PARSE_OBJECT       *Next;
    514 
    515 
    516     DbgPrint (ASL_PARSE_OUTPUT,
    517         "\nLinkPeerOp: 1=%p (%s), 2=%p (%s)\n",
    518         Op1, Op1 ? UtGetOpName(Op1->Asl.ParseOpcode) : NULL,
    519         Op2, Op2 ? UtGetOpName(Op2->Asl.ParseOpcode) : NULL);
    520 
    521 
    522     if ((!Op1) && (!Op2))
    523     {
    524         DbgPrint (ASL_PARSE_OUTPUT, "\nTwo Null ops!\n");
    525         return (Op1);
    526     }
    527 
    528     /* If one of the ops is null, just return the non-null op */
    529 
    530     if (!Op2)
    531     {
    532         return (Op1);
    533     }
    534 
    535     if (!Op1)
    536     {
    537         return (Op2);
    538     }
    539 
    540     if (Op1 == Op2)
    541     {
    542         DbgPrint (ASL_DEBUG_OUTPUT,
    543             "\n************* Internal error, linking op to itself %p\n",
    544             Op1);
    545         AslError (ASL_WARNING, ASL_MSG_COMPILER_INTERNAL, Op1,
    546             "Linking op to itself");
    547         return (Op1);
    548     }
    549 
    550     Op1->Asl.Parent = Op2->Asl.Parent;
    551 
    552     /*
    553      * Op 1 may already have a peer list (such as an IF/ELSE pair),
    554      * so we must walk to the end of the list and attach the new
    555      * peer at the end
    556      */
    557     Next = Op1;
    558     while (Next->Asl.Next)
    559     {
    560         Next = Next->Asl.Next;
    561     }
    562 
    563     Next->Asl.Next = Op2;
    564     return (Op1);
    565 }
    566 
    567 
    568 /*******************************************************************************
    569  *
    570  * FUNCTION:    TrLinkPeerOps
    571  *
    572  * PARAMETERS:  NumPeers            - The number of ops in the list to follow
    573  *              ...                 - A list of ops to link together as peers
    574  *
    575  * RETURN:      The first op in the list (head of the peer list)
    576  *
    577  * DESCRIPTION: Link together an arbitrary number of peer ops.
    578  *
    579  ******************************************************************************/
    580 
    581 ACPI_PARSE_OBJECT *
    582 TrLinkPeerOps (
    583     UINT32                  NumPeers,
    584     ...)
    585 {
    586     ACPI_PARSE_OBJECT       *This;
    587     ACPI_PARSE_OBJECT       *Next;
    588     va_list                 ap;
    589     UINT32                  i;
    590     ACPI_PARSE_OBJECT       *Start;
    591 
    592 
    593     DbgPrint (ASL_PARSE_OUTPUT,
    594         "\nLinkPeerOps: (%u) ", NumPeers);
    595 
    596     va_start (ap, NumPeers);
    597     This = va_arg (ap, ACPI_PARSE_OBJECT *);
    598     Start = This;
    599 
    600     /*
    601      * Link all peers
    602      */
    603     for (i = 0; i < (NumPeers -1); i++)
    604     {
    605         DbgPrint (ASL_PARSE_OUTPUT, "%u=%p ", (i+1), This);
    606 
    607         while (This->Asl.Next)
    608         {
    609             This = This->Asl.Next;
    610         }
    611 
    612         /* Get another peer op */
    613 
    614         Next = va_arg (ap, ACPI_PARSE_OBJECT *);
    615         if (!Next)
    616         {
    617             Next = TrAllocateOp (PARSEOP_DEFAULT_ARG);
    618         }
    619 
    620         /* link new op to the current op */
    621 
    622         This->Asl.Next = Next;
    623         This = Next;
    624     }
    625 
    626     va_end (ap);
    627     DbgPrint (ASL_PARSE_OUTPUT,"\n");
    628     return (Start);
    629 }
    630 
    631 
    632 /*******************************************************************************
    633  *
    634  * FUNCTION:    TrLinkChildOp
    635  *
    636  * PARAMETERS:  Op1           - Parent op
    637  *              Op2           - Op to become a child
    638  *
    639  * RETURN:      The parent op
    640  *
    641  * DESCRIPTION: Link two ops together as a parent and child
    642  *
    643  ******************************************************************************/
    644 
    645 ACPI_PARSE_OBJECT *
    646 TrLinkChildOp (
    647     ACPI_PARSE_OBJECT       *Op1,
    648     ACPI_PARSE_OBJECT       *Op2)
    649 {
    650     ACPI_PARSE_OBJECT       *Next;
    651 
    652 
    653     DbgPrint (ASL_PARSE_OUTPUT,
    654         "\nLinkChildOp: Parent=%p (%s), Child=%p (%s)\n",
    655         Op1, Op1 ? UtGetOpName(Op1->Asl.ParseOpcode): NULL,
    656         Op2, Op2 ? UtGetOpName(Op2->Asl.ParseOpcode): NULL);
    657 
    658     /*
    659      * Converter: if TrLinkChildOp is called to link a method call,
    660      * turn on capture comments as it signifies that we are done parsing
    661      * a method call.
    662      */
    663     if (AcpiGbl_CaptureComments && Op1)
    664     {
    665         if (Op1->Asl.ParseOpcode == PARSEOP_METHODCALL)
    666         {
    667             Gbl_CommentState.CaptureComments = TRUE;
    668         }
    669         Gbl_CommentState.LatestParseOp = Op1;
    670     }
    671 
    672     if (!Op1 || !Op2)
    673     {
    674         return (Op1);
    675     }
    676 
    677     Op1->Asl.Child = Op2;
    678 
    679     /* Set the child and all peers of the child to point to the parent */
    680 
    681     Next = Op2;
    682     while (Next)
    683     {
    684         Next->Asl.Parent = Op1;
    685         Next = Next->Asl.Next;
    686     }
    687 
    688     return (Op1);
    689 }
    690 
    691 
    692 /*******************************************************************************
    693  *
    694  * FUNCTION:    TrWalkParseTree
    695  *
    696  * PARAMETERS:  Op                      - Walk starting point
    697  *              Visitation              - Type of walk
    698  *              DescendingCallback      - Called during tree descent
    699  *              AscendingCallback       - Called during tree ascent
    700  *              Context                 - To be passed to the callbacks
    701  *
    702  * RETURN:      Status from callback(s)
    703  *
    704  * DESCRIPTION: Walk the entire parse tree.
    705  *
    706  ******************************************************************************/
    707 
    708 ACPI_STATUS
    709 TrWalkParseTree (
    710     ACPI_PARSE_OBJECT       *Op,
    711     UINT32                  Visitation,
    712     ASL_WALK_CALLBACK       DescendingCallback,
    713     ASL_WALK_CALLBACK       AscendingCallback,
    714     void                    *Context)
    715 {
    716     UINT32                  Level;
    717     BOOLEAN                 OpPreviouslyVisited;
    718     ACPI_PARSE_OBJECT       *StartOp = Op;
    719     ACPI_STATUS             Status;
    720 
    721 
    722     if (!Gbl_ParseTreeRoot)
    723     {
    724         return (AE_OK);
    725     }
    726 
    727     Level = 0;
    728     OpPreviouslyVisited = FALSE;
    729 
    730     switch (Visitation)
    731     {
    732     case ASL_WALK_VISIT_DOWNWARD:
    733 
    734         while (Op)
    735         {
    736             if (!OpPreviouslyVisited)
    737             {
    738                 /* Let the callback process the op. */
    739 
    740                 Status = DescendingCallback (Op, Level, Context);
    741                 if (ACPI_SUCCESS (Status))
    742                 {
    743                     /* Visit children first, once */
    744 
    745                     if (Op->Asl.Child)
    746                     {
    747                         Level++;
    748                         Op = Op->Asl.Child;
    749                         continue;
    750                     }
    751                 }
    752                 else if (Status != AE_CTRL_DEPTH)
    753                 {
    754                     /* Exit immediately on any error */
    755 
    756                     return (Status);
    757                 }
    758             }
    759 
    760             /* Terminate walk at start op */
    761 
    762             if (Op == StartOp)
    763             {
    764                 break;
    765             }
    766 
    767             /* No more children, visit peers */
    768 
    769             if (Op->Asl.Next)
    770             {
    771                 Op = Op->Asl.Next;
    772                 OpPreviouslyVisited = FALSE;
    773             }
    774             else
    775             {
    776                 /* No children or peers, re-visit parent */
    777 
    778                 if (Level != 0 )
    779                 {
    780                     Level--;
    781                 }
    782                 Op = Op->Asl.Parent;
    783                 OpPreviouslyVisited = TRUE;
    784             }
    785         }
    786         break;
    787 
    788     case ASL_WALK_VISIT_UPWARD:
    789 
    790         while (Op)
    791         {
    792             /* Visit leaf op (no children) or parent op on return trip */
    793 
    794             if ((!Op->Asl.Child) ||
    795                 (OpPreviouslyVisited))
    796             {
    797                 /* Let the callback process the op. */
    798 
    799                 Status = AscendingCallback (Op, Level, Context);
    800                 if (ACPI_FAILURE (Status))
    801                 {
    802                     return (Status);
    803                 }
    804             }
    805             else
    806             {
    807                 /* Visit children first, once */
    808 
    809                 Level++;
    810                 Op = Op->Asl.Child;
    811                 continue;
    812             }
    813 
    814             /* Terminate walk at start op */
    815 
    816             if (Op == StartOp)
    817             {
    818                 break;
    819             }
    820 
    821             /* No more children, visit peers */
    822 
    823             if (Op->Asl.Next)
    824             {
    825                 Op = Op->Asl.Next;
    826                 OpPreviouslyVisited = FALSE;
    827             }
    828             else
    829             {
    830                 /* No children or peers, re-visit parent */
    831 
    832                 if (Level != 0 )
    833                 {
    834                     Level--;
    835                 }
    836                 Op = Op->Asl.Parent;
    837                 OpPreviouslyVisited = TRUE;
    838             }
    839         }
    840         break;
    841 
    842      case ASL_WALK_VISIT_TWICE:
    843 
    844         while (Op)
    845         {
    846             if (OpPreviouslyVisited)
    847             {
    848                 Status = AscendingCallback (Op, Level, Context);
    849                 if (ACPI_FAILURE (Status))
    850                 {
    851                     return (Status);
    852                 }
    853             }
    854             else
    855             {
    856                 /* Let the callback process the op. */
    857 
    858                 Status = DescendingCallback (Op, Level, Context);
    859                 if (ACPI_SUCCESS (Status))
    860                 {
    861                     /* Visit children first, once */
    862 
    863                     if (Op->Asl.Child)
    864                     {
    865                         Level++;
    866                         Op = Op->Asl.Child;
    867                         continue;
    868                     }
    869                 }
    870                 else if (Status != AE_CTRL_DEPTH)
    871                 {
    872                     /* Exit immediately on any error */
    873 
    874                     return (Status);
    875                 }
    876             }
    877 
    878             /* Terminate walk at start op */
    879 
    880             if (Op == StartOp)
    881             {
    882                 break;
    883             }
    884 
    885             /* No more children, visit peers */
    886 
    887             if (Op->Asl.Next)
    888             {
    889                 Op = Op->Asl.Next;
    890                 OpPreviouslyVisited = FALSE;
    891             }
    892             else
    893             {
    894                 /* No children or peers, re-visit parent */
    895 
    896                 if (Level != 0 )
    897                 {
    898                     Level--;
    899                 }
    900                 Op = Op->Asl.Parent;
    901                 OpPreviouslyVisited = TRUE;
    902             }
    903         }
    904         break;
    905 
    906     default:
    907         /* No other types supported */
    908         break;
    909     }
    910 
    911     /* If we get here, the walk completed with no errors */
    912 
    913     return (AE_OK);
    914 }
    915