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[mirror_ubuntu-artful-kernel.git] / drivers / acpi / acpica / utresrc.c

/*******************************************************************************
 *
 * Module Name: utresrc - Resource management utilities
 *
 ******************************************************************************/

/*
 * Copyright (C) 2000 - 2016, Intel Corp.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions, and the following disclaimer,
 *    without modification.
 * 2. Redistributions in binary form must reproduce at minimum a disclaimer
 *    substantially similar to the "NO WARRANTY" disclaimer below
 *    ("Disclaimer") and any redistribution must be conditioned upon
 *    including a substantially similar Disclaimer requirement for further
 *    binary redistribution.
 * 3. Neither the names of the above-listed copyright holders nor the names
 *    of any contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * Alternatively, this software may be distributed under the terms of the
 * GNU General Public License ("GPL") version 2 as published by the Free
 * Software Foundation.
 *
 * NO WARRANTY
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGES.
 */

#include <acpi/acpi.h>
#include "accommon.h"
#include "acresrc.h"

#define _COMPONENT          ACPI_UTILITIES
ACPI_MODULE_NAME("utresrc")

#if defined(ACPI_DEBUG_OUTPUT) || defined (ACPI_DISASSEMBLER) || defined (ACPI_DEBUGGER)
/*
 * Strings used to decode resource descriptors.
 * Used by both the disassembler and the debugger resource dump routines
 */
const char *acpi_gbl_bm_decode[] = {
        "NotBusMaster",
        "BusMaster"
};

const char *acpi_gbl_config_decode[] = {
        "0 - Good Configuration",
        "1 - Acceptable Configuration",
        "2 - Suboptimal Configuration",
        "3 - ***Invalid Configuration***",
};

const char *acpi_gbl_consume_decode[] = {
        "ResourceProducer",
        "ResourceConsumer"
};

const char *acpi_gbl_dec_decode[] = {
        "PosDecode",
        "SubDecode"
};

const char *acpi_gbl_he_decode[] = {
        "Level",
        "Edge"
};

const char *acpi_gbl_io_decode[] = {
        "Decode10",
        "Decode16"
};

const char *acpi_gbl_ll_decode[] = {
        "ActiveHigh",
        "ActiveLow",
        "ActiveBoth",
        "Reserved"
};

const char *acpi_gbl_max_decode[] = {
        "MaxNotFixed",
        "MaxFixed"
};

const char *acpi_gbl_mem_decode[] = {
        "NonCacheable",
        "Cacheable",
        "WriteCombining",
        "Prefetchable"
};

const char *acpi_gbl_min_decode[] = {
        "MinNotFixed",
        "MinFixed"
};

const char *acpi_gbl_mtp_decode[] = {
        "AddressRangeMemory",
        "AddressRangeReserved",
        "AddressRangeACPI",
        "AddressRangeNVS"
};

const char *acpi_gbl_rng_decode[] = {
        "InvalidRanges",
        "NonISAOnlyRanges",
        "ISAOnlyRanges",
        "EntireRange"
};

const char *acpi_gbl_rw_decode[] = {
        "ReadOnly",
        "ReadWrite"
};

const char *acpi_gbl_shr_decode[] = {
        "Exclusive",
        "Shared",
        "ExclusiveAndWake",     /* ACPI 5.0 */
        "SharedAndWake"         /* ACPI 5.0 */
};

const char *acpi_gbl_siz_decode[] = {
        "Transfer8",
        "Transfer8_16",
        "Transfer16",
        "InvalidSize"
};

const char *acpi_gbl_trs_decode[] = {
        "DenseTranslation",
        "SparseTranslation"
};

const char *acpi_gbl_ttp_decode[] = {
        "TypeStatic",
        "TypeTranslation"
};

const char *acpi_gbl_typ_decode[] = {
        "Compatibility",
        "TypeA",
        "TypeB",
        "TypeF"
};

const char *acpi_gbl_ppc_decode[] = {
        "PullDefault",
        "PullUp",
        "PullDown",
        "PullNone"
};

const char *acpi_gbl_ior_decode[] = {
        "IoRestrictionNone",
        "IoRestrictionInputOnly",
        "IoRestrictionOutputOnly",
        "IoRestrictionNoneAndPreserve"
};

const char *acpi_gbl_dts_decode[] = {
        "Width8bit",
        "Width16bit",
        "Width32bit",
        "Width64bit",
        "Width128bit",
        "Width256bit",
};

/* GPIO connection type */

const char *acpi_gbl_ct_decode[] = {
        "Interrupt",
        "I/O"
};

/* Serial bus type */

const char *acpi_gbl_sbt_decode[] = {
        "/* UNKNOWN serial bus type */",
        "I2C",
        "SPI",
        "UART"
};

/* I2C serial bus access mode */

const char *acpi_gbl_am_decode[] = {
        "AddressingMode7Bit",
        "AddressingMode10Bit"
};

/* I2C serial bus slave mode */

const char *acpi_gbl_sm_decode[] = {
        "ControllerInitiated",
        "DeviceInitiated"
};

/* SPI serial bus wire mode */

const char *acpi_gbl_wm_decode[] = {
        "FourWireMode",
        "ThreeWireMode"
};

/* SPI serial clock phase */

const char *acpi_gbl_cph_decode[] = {
        "ClockPhaseFirst",
        "ClockPhaseSecond"
};

/* SPI serial bus clock polarity */

const char *acpi_gbl_cpo_decode[] = {
        "ClockPolarityLow",
        "ClockPolarityHigh"
};

/* SPI serial bus device polarity */

const char *acpi_gbl_dp_decode[] = {
        "PolarityLow",
        "PolarityHigh"
};

/* UART serial bus endian */

const char *acpi_gbl_ed_decode[] = {
        "LittleEndian",
        "BigEndian"
};

/* UART serial bus bits per byte */

const char *acpi_gbl_bpb_decode[] = {
        "DataBitsFive",
        "DataBitsSix",
        "DataBitsSeven",
        "DataBitsEight",
        "DataBitsNine",
        "/* UNKNOWN Bits per byte */",
        "/* UNKNOWN Bits per byte */",
        "/* UNKNOWN Bits per byte */"
};

/* UART serial bus stop bits */

const char *acpi_gbl_sb_decode[] = {
        "StopBitsZero",
        "StopBitsOne",
        "StopBitsOnePlusHalf",
        "StopBitsTwo"
};

/* UART serial bus flow control */

const char *acpi_gbl_fc_decode[] = {
        "FlowControlNone",
        "FlowControlHardware",
        "FlowControlXON",
        "/* UNKNOWN flow control keyword */"
};

/* UART serial bus parity type */

const char *acpi_gbl_pt_decode[] = {
        "ParityTypeNone",
        "ParityTypeEven",
        "ParityTypeOdd",
        "ParityTypeMark",
        "ParityTypeSpace",
        "/* UNKNOWN parity keyword */",
        "/* UNKNOWN parity keyword */",
        "/* UNKNOWN parity keyword */"
};

#endif

/*
 * Base sizes of the raw AML resource descriptors, indexed by resource type.
 * Zero indicates a reserved (and therefore invalid) resource type.
 */
const u8 acpi_gbl_resource_aml_sizes[] = {
        /* Small descriptors */

        0,
        0,
        0,
        0,
        ACPI_AML_SIZE_SMALL(struct aml_resource_irq),
        ACPI_AML_SIZE_SMALL(struct aml_resource_dma),
        ACPI_AML_SIZE_SMALL(struct aml_resource_start_dependent),
        ACPI_AML_SIZE_SMALL(struct aml_resource_end_dependent),
        ACPI_AML_SIZE_SMALL(struct aml_resource_io),
        ACPI_AML_SIZE_SMALL(struct aml_resource_fixed_io),
        ACPI_AML_SIZE_SMALL(struct aml_resource_fixed_dma),
        0,
        0,
        0,
        ACPI_AML_SIZE_SMALL(struct aml_resource_vendor_small),
        ACPI_AML_SIZE_SMALL(struct aml_resource_end_tag),

        /* Large descriptors */

        0,
        ACPI_AML_SIZE_LARGE(struct aml_resource_memory24),
        ACPI_AML_SIZE_LARGE(struct aml_resource_generic_register),
        0,
        ACPI_AML_SIZE_LARGE(struct aml_resource_vendor_large),
        ACPI_AML_SIZE_LARGE(struct aml_resource_memory32),
        ACPI_AML_SIZE_LARGE(struct aml_resource_fixed_memory32),
        ACPI_AML_SIZE_LARGE(struct aml_resource_address32),
        ACPI_AML_SIZE_LARGE(struct aml_resource_address16),
        ACPI_AML_SIZE_LARGE(struct aml_resource_extended_irq),
        ACPI_AML_SIZE_LARGE(struct aml_resource_address64),
        ACPI_AML_SIZE_LARGE(struct aml_resource_extended_address64),
        ACPI_AML_SIZE_LARGE(struct aml_resource_gpio),
        0,
        ACPI_AML_SIZE_LARGE(struct aml_resource_common_serialbus),
};

const u8 acpi_gbl_resource_aml_serial_bus_sizes[] = {
        0,
        ACPI_AML_SIZE_LARGE(struct aml_resource_i2c_serialbus),
        ACPI_AML_SIZE_LARGE(struct aml_resource_spi_serialbus),
        ACPI_AML_SIZE_LARGE(struct aml_resource_uart_serialbus),
};

/*
 * Resource types, used to validate the resource length field.
 * The length of fixed-length types must match exactly, variable
 * lengths must meet the minimum required length, etc.
 * Zero indicates a reserved (and therefore invalid) resource type.
 */
static const u8 acpi_gbl_resource_types[] = {
        /* Small descriptors */

        0,
        0,
        0,
        0,
        ACPI_SMALL_VARIABLE_LENGTH,     /* 04 IRQ */
        ACPI_FIXED_LENGTH,      /* 05 DMA */
        ACPI_SMALL_VARIABLE_LENGTH,     /* 06 start_dependent_functions */
        ACPI_FIXED_LENGTH,      /* 07 end_dependent_functions */
        ACPI_FIXED_LENGTH,      /* 08 IO */
        ACPI_FIXED_LENGTH,      /* 09 fixed_IO */
        ACPI_FIXED_LENGTH,      /* 0A fixed_DMA */
        0,
        0,
        0,
        ACPI_VARIABLE_LENGTH,   /* 0E vendor_short */
        ACPI_FIXED_LENGTH,      /* 0F end_tag */

        /* Large descriptors */

        0,
        ACPI_FIXED_LENGTH,      /* 01 Memory24 */
        ACPI_FIXED_LENGTH,      /* 02 generic_register */
        0,
        ACPI_VARIABLE_LENGTH,   /* 04 vendor_long */
        ACPI_FIXED_LENGTH,      /* 05 Memory32 */
        ACPI_FIXED_LENGTH,      /* 06 memory32_fixed */
        ACPI_VARIABLE_LENGTH,   /* 07 Dword* address */
        ACPI_VARIABLE_LENGTH,   /* 08 Word* address */
        ACPI_VARIABLE_LENGTH,   /* 09 extended_IRQ */
        ACPI_VARIABLE_LENGTH,   /* 0A Qword* address */
        ACPI_FIXED_LENGTH,      /* 0B Extended* address */
        ACPI_VARIABLE_LENGTH,   /* 0C Gpio* */
        0,
        ACPI_VARIABLE_LENGTH    /* 0E *serial_bus */
};

/*******************************************************************************
 *
 * FUNCTION:    acpi_ut_walk_aml_resources
 *
 * PARAMETERS:  walk_state          - Current walk info
 * PARAMETERS:  aml                 - Pointer to the raw AML resource template
 *              aml_length          - Length of the entire template
 *              user_function       - Called once for each descriptor found. If
 *                                    NULL, a pointer to the end_tag is returned
 *              context             - Passed to user_function
 *
 * RETURN:      Status
 *
 * DESCRIPTION: Walk a raw AML resource list(buffer). User function called
 *              once for each resource found.
 *
 ******************************************************************************/

acpi_status
acpi_ut_walk_aml_resources(struct acpi_walk_state *walk_state,
                           u8 *aml,
                           acpi_size aml_length,
                           acpi_walk_aml_callback user_function, void **context)
{
        acpi_status status;
        u8 *end_aml;
        u8 resource_index;
        u32 length;
        u32 offset = 0;
        u8 end_tag[2] = { 0x79, 0x00 };

        ACPI_FUNCTION_TRACE(ut_walk_aml_resources);

        /* The absolute minimum resource template is one end_tag descriptor */

        if (aml_length < sizeof(struct aml_resource_end_tag)) {
                return_ACPI_STATUS(AE_AML_NO_RESOURCE_END_TAG);
        }

        /* Point to the end of the resource template buffer */

        end_aml = aml + aml_length;

        /* Walk the byte list, abort on any invalid descriptor type or length */

        while (aml < end_aml) {

                /* Validate the Resource Type and Resource Length */

                status =
                    acpi_ut_validate_resource(walk_state, aml, &resource_index);
                if (ACPI_FAILURE(status)) {
                        /*
                         * Exit on failure. Cannot continue because the descriptor
                         * length may be bogus also.
                         */
                        return_ACPI_STATUS(status);
                }

                /* Get the length of this descriptor */

                length = acpi_ut_get_descriptor_length(aml);

                /* Invoke the user function */

                if (user_function) {
                        status =
                            user_function(aml, length, offset, resource_index,
                                          context);
                        if (ACPI_FAILURE(status)) {
                                return_ACPI_STATUS(status);
                        }
                }

                /* An end_tag descriptor terminates this resource template */

                if (acpi_ut_get_resource_type(aml) ==
                    ACPI_RESOURCE_NAME_END_TAG) {
                        /*
                         * There must be at least one more byte in the buffer for
                         * the 2nd byte of the end_tag
                         */
                        if ((aml + 1) >= end_aml) {
                                return_ACPI_STATUS(AE_AML_NO_RESOURCE_END_TAG);
                        }

                        /* Return the pointer to the end_tag if requested */

                        if (!user_function) {
                                *context = aml;
                        }

                        /* Normal exit */

                        return_ACPI_STATUS(AE_OK);
                }

                aml += length;
                offset += length;
        }

        /* Did not find an end_tag descriptor */

        if (user_function) {

                /* Insert an end_tag anyway. acpi_rs_get_list_length always leaves room */

                (void)acpi_ut_validate_resource(walk_state, end_tag,
                                                &resource_index);
                status =
                    user_function(end_tag, 2, offset, resource_index, context);
                if (ACPI_FAILURE(status)) {
                        return_ACPI_STATUS(status);
                }
        }

        return_ACPI_STATUS(AE_AML_NO_RESOURCE_END_TAG);
}

/*******************************************************************************
 *
 * FUNCTION:    acpi_ut_validate_resource
 *
 * PARAMETERS:  walk_state          - Current walk info
 *              aml                 - Pointer to the raw AML resource descriptor
 *              return_index        - Where the resource index is returned. NULL
 *                                    if the index is not required.
 *
 * RETURN:      Status, and optionally the Index into the global resource tables
 *
 * DESCRIPTION: Validate an AML resource descriptor by checking the Resource
 *              Type and Resource Length. Returns an index into the global
 *              resource information/dispatch tables for later use.
 *
 ******************************************************************************/

acpi_status
acpi_ut_validate_resource(struct acpi_walk_state *walk_state,
                          void *aml, u8 *return_index)
{
        union aml_resource *aml_resource;
        u8 resource_type;
        u8 resource_index;
        acpi_rs_length resource_length;
        acpi_rs_length minimum_resource_length;

        ACPI_FUNCTION_ENTRY();

        /*
         * 1) Validate the resource_type field (Byte 0)
         */
        resource_type = ACPI_GET8(aml);

        /*
         * Byte 0 contains the descriptor name (Resource Type)
         * Examine the large/small bit in the resource header
         */
        if (resource_type & ACPI_RESOURCE_NAME_LARGE) {

                /* Verify the large resource type (name) against the max */

                if (resource_type > ACPI_RESOURCE_NAME_LARGE_MAX) {
                        goto invalid_resource;
                }

                /*
                 * Large Resource Type -- bits 6:0 contain the name
                 * Translate range 0x80-0x8B to index range 0x10-0x1B
                 */
                resource_index = (u8) (resource_type - 0x70);
        } else {
                /*
                 * Small Resource Type -- bits 6:3 contain the name
                 * Shift range to index range 0x00-0x0F
                 */
                resource_index = (u8)
                    ((resource_type & ACPI_RESOURCE_NAME_SMALL_MASK) >> 3);
        }

        /*
         * Check validity of the resource type, via acpi_gbl_resource_types.
         * Zero indicates an invalid resource.
         */
        if (!acpi_gbl_resource_types[resource_index]) {
                goto invalid_resource;
        }

        /*
         * Validate the resource_length field. This ensures that the length
         * is at least reasonable, and guarantees that it is non-zero.
         */
        resource_length = acpi_ut_get_resource_length(aml);
        minimum_resource_length = acpi_gbl_resource_aml_sizes[resource_index];

        /* Validate based upon the type of resource - fixed length or variable */

        switch (acpi_gbl_resource_types[resource_index]) {
        case ACPI_FIXED_LENGTH:

                /* Fixed length resource, length must match exactly */

                if (resource_length != minimum_resource_length) {
                        goto bad_resource_length;
                }
                break;

        case ACPI_VARIABLE_LENGTH:

                /* Variable length resource, length must be at least the minimum */

                if (resource_length < minimum_resource_length) {
                        goto bad_resource_length;
                }
                break;

        case ACPI_SMALL_VARIABLE_LENGTH:

                /* Small variable length resource, length can be (Min) or (Min-1) */

                if ((resource_length > minimum_resource_length) ||
                    (resource_length < (minimum_resource_length - 1))) {
                        goto bad_resource_length;
                }
                break;

        default:

                /* Shouldn't happen (because of validation earlier), but be sure */

                goto invalid_resource;
        }

        aml_resource = ACPI_CAST_PTR(union aml_resource, aml);
        if (resource_type == ACPI_RESOURCE_NAME_SERIAL_BUS) {

                /* Validate the bus_type field */

                if ((aml_resource->common_serial_bus.type == 0) ||
                    (aml_resource->common_serial_bus.type >
                     AML_RESOURCE_MAX_SERIALBUSTYPE)) {
                        if (walk_state) {
                                ACPI_ERROR((AE_INFO,
                                            "Invalid/unsupported SerialBus resource descriptor: BusType 0x%2.2X",
                                            aml_resource->common_serial_bus.
                                            type));
                        }
                        return (AE_AML_INVALID_RESOURCE_TYPE);
                }
        }

        /* Optionally return the resource table index */

        if (return_index) {
                *return_index = resource_index;
        }

        return (AE_OK);

invalid_resource:

        if (walk_state) {
                ACPI_ERROR((AE_INFO,
                            "Invalid/unsupported resource descriptor: Type 0x%2.2X",
                            resource_type));
        }
        return (AE_AML_INVALID_RESOURCE_TYPE);

bad_resource_length:

        if (walk_state) {
                ACPI_ERROR((AE_INFO,
                            "Invalid resource descriptor length: Type "
                            "0x%2.2X, Length 0x%4.4X, MinLength 0x%4.4X",
                            resource_type, resource_length,
                            minimum_resource_length));
        }
        return (AE_AML_BAD_RESOURCE_LENGTH);
}

/*******************************************************************************
 *
 * FUNCTION:    acpi_ut_get_resource_type
 *
 * PARAMETERS:  aml             - Pointer to the raw AML resource descriptor
 *
 * RETURN:      The Resource Type with no extraneous bits (except the
 *              Large/Small descriptor bit -- this is left alone)
 *
 * DESCRIPTION: Extract the Resource Type/Name from the first byte of
 *              a resource descriptor.
 *
 ******************************************************************************/

u8 acpi_ut_get_resource_type(void *aml)
{
        ACPI_FUNCTION_ENTRY();

        /*
         * Byte 0 contains the descriptor name (Resource Type)
         * Examine the large/small bit in the resource header
         */
        if (ACPI_GET8(aml) & ACPI_RESOURCE_NAME_LARGE) {

                /* Large Resource Type -- bits 6:0 contain the name */

                return (ACPI_GET8(aml));
        } else {
                /* Small Resource Type -- bits 6:3 contain the name */

                return ((u8) (ACPI_GET8(aml) & ACPI_RESOURCE_NAME_SMALL_MASK));
        }
}

/*******************************************************************************
 *
 * FUNCTION:    acpi_ut_get_resource_length
 *
 * PARAMETERS:  aml             - Pointer to the raw AML resource descriptor
 *
 * RETURN:      Byte Length
 *
 * DESCRIPTION: Get the "Resource Length" of a raw AML descriptor. By
 *              definition, this does not include the size of the descriptor
 *              header or the length field itself.
 *
 ******************************************************************************/

u16 acpi_ut_get_resource_length(void *aml)
{
        acpi_rs_length resource_length;

        ACPI_FUNCTION_ENTRY();

        /*
         * Byte 0 contains the descriptor name (Resource Type)
         * Examine the large/small bit in the resource header
         */
        if (ACPI_GET8(aml) & ACPI_RESOURCE_NAME_LARGE) {

                /* Large Resource type -- bytes 1-2 contain the 16-bit length */

                ACPI_MOVE_16_TO_16(&resource_length, ACPI_ADD_PTR(u8, aml, 1));

        } else {
                /* Small Resource type -- bits 2:0 of byte 0 contain the length */

                resource_length = (u16) (ACPI_GET8(aml) &
                                         ACPI_RESOURCE_NAME_SMALL_LENGTH_MASK);
        }

        return (resource_length);
}

/*******************************************************************************
 *
 * FUNCTION:    acpi_ut_get_resource_header_length
 *
 * PARAMETERS:  aml             - Pointer to the raw AML resource descriptor
 *
 * RETURN:      Length of the AML header (depends on large/small descriptor)
 *
 * DESCRIPTION: Get the length of the header for this resource.
 *
 ******************************************************************************/

u8 acpi_ut_get_resource_header_length(void *aml)
{
        ACPI_FUNCTION_ENTRY();

        /* Examine the large/small bit in the resource header */

        if (ACPI_GET8(aml) & ACPI_RESOURCE_NAME_LARGE) {
                return (sizeof(struct aml_resource_large_header));
        } else {
                return (sizeof(struct aml_resource_small_header));
        }
}

/*******************************************************************************
 *
 * FUNCTION:    acpi_ut_get_descriptor_length
 *
 * PARAMETERS:  aml             - Pointer to the raw AML resource descriptor
 *
 * RETURN:      Byte length
 *
 * DESCRIPTION: Get the total byte length of a raw AML descriptor, including the
 *              length of the descriptor header and the length field itself.
 *              Used to walk descriptor lists.
 *
 ******************************************************************************/

u32 acpi_ut_get_descriptor_length(void *aml)
{
        ACPI_FUNCTION_ENTRY();

        /*
         * Get the Resource Length (does not include header length) and add
         * the header length (depends on if this is a small or large resource)
         */
        return (acpi_ut_get_resource_length(aml) +
                acpi_ut_get_resource_header_length(aml));
}

/*******************************************************************************
 *
 * FUNCTION:    acpi_ut_get_resource_end_tag
 *
 * PARAMETERS:  obj_desc        - The resource template buffer object
 *              end_tag         - Where the pointer to the end_tag is returned
 *
 * RETURN:      Status, pointer to the end tag
 *
 * DESCRIPTION: Find the end_tag resource descriptor in an AML resource template
 *              Note: allows a buffer length of zero.
 *
 ******************************************************************************/

acpi_status
acpi_ut_get_resource_end_tag(union acpi_operand_object *obj_desc, u8 **end_tag)
{
        acpi_status status;

        ACPI_FUNCTION_TRACE(ut_get_resource_end_tag);

        /* Allow a buffer length of zero */

        if (!obj_desc->buffer.length) {
                *end_tag = obj_desc->buffer.pointer;
                return_ACPI_STATUS(AE_OK);
        }

        /* Validate the template and get a pointer to the end_tag */

        status = acpi_ut_walk_aml_resources(NULL, obj_desc->buffer.pointer,
                                            obj_desc->buffer.length, NULL,
                                            (void **)end_tag);

        return_ACPI_STATUS(status);
}