Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

[cris-mirror.git] / drivers / acpi / acpica / hwregs.c

/*******************************************************************************
 *
 * Module Name: hwregs - Read/write access functions for the various ACPI
 *                       control and status registers.
 *
 ******************************************************************************/

/*
 * Copyright (C) 2000 - 2018, 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 "acevents.h"

#define _COMPONENT          ACPI_HARDWARE
ACPI_MODULE_NAME("hwregs")

#if (!ACPI_REDUCED_HARDWARE)
/* Local Prototypes */
static u8
acpi_hw_get_access_bit_width(u64 address,
                             struct acpi_generic_address *reg,
                             u8 max_bit_width);

static acpi_status
acpi_hw_read_multiple(u32 *value,
                      struct acpi_generic_address *register_a,
                      struct acpi_generic_address *register_b);

static acpi_status
acpi_hw_write_multiple(u32 value,
                       struct acpi_generic_address *register_a,
                       struct acpi_generic_address *register_b);

#endif                          /* !ACPI_REDUCED_HARDWARE */

/******************************************************************************
 *
 * FUNCTION:    acpi_hw_get_access_bit_width
 *
 * PARAMETERS:  address             - GAS register address
 *              reg                 - GAS register structure
 *              max_bit_width       - Max bit_width supported (32 or 64)
 *
 * RETURN:      Status
 *
 * DESCRIPTION: Obtain optimal access bit width
 *
 ******************************************************************************/

static u8
acpi_hw_get_access_bit_width(u64 address,
                             struct acpi_generic_address *reg, u8 max_bit_width)
{
        u8 access_bit_width;

        /*
         * GAS format "register", used by FADT:
         *  1. Detected if bit_offset is 0 and bit_width is 8/16/32/64;
         *  2. access_size field is ignored and bit_width field is used for
         *     determining the boundary of the IO accesses.
         * GAS format "region", used by APEI registers:
         *  1. Detected if bit_offset is not 0 or bit_width is not 8/16/32/64;
         *  2. access_size field is used for determining the boundary of the
         *     IO accesses;
         *  3. bit_offset/bit_width fields are used to describe the "region".
         *
         * Note: This algorithm assumes that the "Address" fields should always
         *       contain aligned values.
         */
        if (!reg->bit_offset && reg->bit_width &&
            ACPI_IS_POWER_OF_TWO(reg->bit_width) &&
            ACPI_IS_ALIGNED(reg->bit_width, 8)) {
                access_bit_width = reg->bit_width;
        } else if (reg->access_width) {
                access_bit_width = ACPI_ACCESS_BIT_WIDTH(reg->access_width);
        } else {
                access_bit_width =
                    ACPI_ROUND_UP_POWER_OF_TWO_8(reg->bit_offset +
                                                 reg->bit_width);
                if (access_bit_width <= 8) {
                        access_bit_width = 8;
                } else {
                        while (!ACPI_IS_ALIGNED(address, access_bit_width >> 3)) {
                                access_bit_width >>= 1;
                        }
                }
        }

        /* Maximum IO port access bit width is 32 */

        if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_IO) {
                max_bit_width = 32;
        }

        /*
         * Return access width according to the requested maximum access bit width,
         * as the caller should know the format of the register and may enforce
         * a 32-bit accesses.
         */
        if (access_bit_width < max_bit_width) {
                return (access_bit_width);
        }
        return (max_bit_width);
}

/******************************************************************************
 *
 * FUNCTION:    acpi_hw_validate_register
 *
 * PARAMETERS:  reg                 - GAS register structure
 *              max_bit_width       - Max bit_width supported (32 or 64)
 *              address             - Pointer to where the gas->address
 *                                    is returned
 *
 * RETURN:      Status
 *
 * DESCRIPTION: Validate the contents of a GAS register. Checks the GAS
 *              pointer, Address, space_id, bit_width, and bit_offset.
 *
 ******************************************************************************/

acpi_status
acpi_hw_validate_register(struct acpi_generic_address *reg,
                          u8 max_bit_width, u64 *address)
{
        u8 bit_width;
        u8 access_width;

        /* Must have a valid pointer to a GAS structure */

        if (!reg) {
                return (AE_BAD_PARAMETER);
        }

        /*
         * Copy the target address. This handles possible alignment issues.
         * Address must not be null. A null address also indicates an optional
         * ACPI register that is not supported, so no error message.
         */
        ACPI_MOVE_64_TO_64(address, &reg->address);
        if (!(*address)) {
                return (AE_BAD_ADDRESS);
        }

        /* Validate the space_ID */

        if ((reg->space_id != ACPI_ADR_SPACE_SYSTEM_MEMORY) &&
            (reg->space_id != ACPI_ADR_SPACE_SYSTEM_IO)) {
                ACPI_ERROR((AE_INFO,
                            "Unsupported address space: 0x%X", reg->space_id));
                return (AE_SUPPORT);
        }

        /* Validate the access_width */

        if (reg->access_width > 4) {
                ACPI_ERROR((AE_INFO,
                            "Unsupported register access width: 0x%X",
                            reg->access_width));
                return (AE_SUPPORT);
        }

        /* Validate the bit_width, convert access_width into number of bits */

        access_width =
            acpi_hw_get_access_bit_width(*address, reg, max_bit_width);
        bit_width =
            ACPI_ROUND_UP(reg->bit_offset + reg->bit_width, access_width);
        if (max_bit_width < bit_width) {
                ACPI_WARNING((AE_INFO,
                              "Requested bit width 0x%X is smaller than register bit width 0x%X",
                              max_bit_width, bit_width));
                return (AE_SUPPORT);
        }

        return (AE_OK);
}

/******************************************************************************
 *
 * FUNCTION:    acpi_hw_read
 *
 * PARAMETERS:  value               - Where the value is returned
 *              reg                 - GAS register structure
 *
 * RETURN:      Status
 *
 * DESCRIPTION: Read from either memory or IO space. This is a 64-bit max
 *              version of acpi_read.
 *
 * LIMITATIONS: <These limitations also apply to acpi_hw_write>
 *      space_ID must be system_memory or system_IO.
 *
 ******************************************************************************/

acpi_status acpi_hw_read(u64 *value, struct acpi_generic_address *reg)
{
        u64 address;
        u8 access_width;
        u32 bit_width;
        u8 bit_offset;
        u64 value64;
        u32 value32;
        u8 index;
        acpi_status status;

        ACPI_FUNCTION_NAME(hw_read);

        /* Validate contents of the GAS register */

        status = acpi_hw_validate_register(reg, 64, &address);
        if (ACPI_FAILURE(status)) {
                return (status);
        }

        /*
         * Initialize entire 64-bit return value to zero, convert access_width
         * into number of bits based
         */
        *value = 0;
        access_width = acpi_hw_get_access_bit_width(address, reg, 64);
        bit_width = reg->bit_offset + reg->bit_width;
        bit_offset = reg->bit_offset;

        /*
         * Two address spaces supported: Memory or IO. PCI_Config is
         * not supported here because the GAS structure is insufficient
         */
        index = 0;
        while (bit_width) {
                if (bit_offset >= access_width) {
                        value64 = 0;
                        bit_offset -= access_width;
                } else {
                        if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
                                status =
                                    acpi_os_read_memory((acpi_physical_address)
                                                        address +
                                                        index *
                                                        ACPI_DIV_8
                                                        (access_width),
                                                        &value64, access_width);
                        } else {        /* ACPI_ADR_SPACE_SYSTEM_IO, validated earlier */

                                status = acpi_hw_read_port((acpi_io_address)
                                                           address +
                                                           index *
                                                           ACPI_DIV_8
                                                           (access_width),
                                                           &value32,
                                                           access_width);
                                value64 = (u64)value32;
                        }
                }

                /*
                 * Use offset style bit writes because "Index * AccessWidth" is
                 * ensured to be less than 64-bits by acpi_hw_validate_register().
                 */
                ACPI_SET_BITS(value, index * access_width,
                              ACPI_MASK_BITS_ABOVE_64(access_width), value64);

                bit_width -=
                    bit_width > access_width ? access_width : bit_width;
                index++;
        }

        ACPI_DEBUG_PRINT((ACPI_DB_IO,
                          "Read:  %8.8X%8.8X width %2d from %8.8X%8.8X (%s)\n",
                          ACPI_FORMAT_UINT64(*value), access_width,
                          ACPI_FORMAT_UINT64(address),
                          acpi_ut_get_region_name(reg->space_id)));

        return (status);
}

/******************************************************************************
 *
 * FUNCTION:    acpi_hw_write
 *
 * PARAMETERS:  value               - Value to be written
 *              reg                 - GAS register structure
 *
 * RETURN:      Status
 *
 * DESCRIPTION: Write to either memory or IO space. This is a 64-bit max
 *              version of acpi_write.
 *
 ******************************************************************************/

acpi_status acpi_hw_write(u64 value, struct acpi_generic_address *reg)
{
        u64 address;
        u8 access_width;
        u32 bit_width;
        u8 bit_offset;
        u64 value64;
        u8 index;
        acpi_status status;

        ACPI_FUNCTION_NAME(hw_write);

        /* Validate contents of the GAS register */

        status = acpi_hw_validate_register(reg, 64, &address);
        if (ACPI_FAILURE(status)) {
                return (status);
        }

        /* Convert access_width into number of bits based */

        access_width = acpi_hw_get_access_bit_width(address, reg, 64);
        bit_width = reg->bit_offset + reg->bit_width;
        bit_offset = reg->bit_offset;

        /*
         * Two address spaces supported: Memory or IO. PCI_Config is
         * not supported here because the GAS structure is insufficient
         */
        index = 0;
        while (bit_width) {
                /*
                 * Use offset style bit reads because "Index * AccessWidth" is
                 * ensured to be less than 64-bits by acpi_hw_validate_register().
                 */
                value64 = ACPI_GET_BITS(&value, index * access_width,
                                        ACPI_MASK_BITS_ABOVE_64(access_width));

                if (bit_offset >= access_width) {
                        bit_offset -= access_width;
                } else {
                        if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
                                status =
                                    acpi_os_write_memory((acpi_physical_address)
                                                         address +
                                                         index *
                                                         ACPI_DIV_8
                                                         (access_width),
                                                         value64, access_width);
                        } else {        /* ACPI_ADR_SPACE_SYSTEM_IO, validated earlier */

                                status = acpi_hw_write_port((acpi_io_address)
                                                            address +
                                                            index *
                                                            ACPI_DIV_8
                                                            (access_width),
                                                            (u32)value64,
                                                            access_width);
                        }
                }

                /*
                 * Index * access_width is ensured to be less than 32-bits by
                 * acpi_hw_validate_register().
                 */
                bit_width -=
                    bit_width > access_width ? access_width : bit_width;
                index++;
        }

        ACPI_DEBUG_PRINT((ACPI_DB_IO,
                          "Wrote: %8.8X%8.8X width %2d   to %8.8X%8.8X (%s)\n",
                          ACPI_FORMAT_UINT64(value), access_width,
                          ACPI_FORMAT_UINT64(address),
                          acpi_ut_get_region_name(reg->space_id)));

        return (status);
}

#if (!ACPI_REDUCED_HARDWARE)
/*******************************************************************************
 *
 * FUNCTION:    acpi_hw_clear_acpi_status
 *
 * PARAMETERS:  None
 *
 * RETURN:      Status
 *
 * DESCRIPTION: Clears all fixed and general purpose status bits
 *
 ******************************************************************************/

acpi_status acpi_hw_clear_acpi_status(void)
{
        acpi_status status;
        acpi_cpu_flags lock_flags = 0;

        ACPI_FUNCTION_TRACE(hw_clear_acpi_status);

        ACPI_DEBUG_PRINT((ACPI_DB_IO, "About to write %04X to %8.8X%8.8X\n",
                          ACPI_BITMASK_ALL_FIXED_STATUS,
                          ACPI_FORMAT_UINT64(acpi_gbl_xpm1a_status.address)));

        lock_flags = acpi_os_acquire_lock(acpi_gbl_hardware_lock);

        /* Clear the fixed events in PM1 A/B */

        status = acpi_hw_register_write(ACPI_REGISTER_PM1_STATUS,
                                        ACPI_BITMASK_ALL_FIXED_STATUS);

        acpi_os_release_lock(acpi_gbl_hardware_lock, lock_flags);

        if (ACPI_FAILURE(status)) {
                goto exit;
        }

        /* Clear the GPE Bits in all GPE registers in all GPE blocks */

        status = acpi_ev_walk_gpe_list(acpi_hw_clear_gpe_block, NULL);

exit:
        return_ACPI_STATUS(status);
}

/*******************************************************************************
 *
 * FUNCTION:    acpi_hw_get_bit_register_info
 *
 * PARAMETERS:  register_id         - Index of ACPI Register to access
 *
 * RETURN:      The bitmask to be used when accessing the register
 *
 * DESCRIPTION: Map register_id into a register bitmask.
 *
 ******************************************************************************/

struct acpi_bit_register_info *acpi_hw_get_bit_register_info(u32 register_id)
{
        ACPI_FUNCTION_ENTRY();

        if (register_id > ACPI_BITREG_MAX) {
                ACPI_ERROR((AE_INFO, "Invalid BitRegister ID: 0x%X",
                            register_id));
                return (NULL);
        }

        return (&acpi_gbl_bit_register_info[register_id]);
}

/******************************************************************************
 *
 * FUNCTION:    acpi_hw_write_pm1_control
 *
 * PARAMETERS:  pm1a_control        - Value to be written to PM1A control
 *              pm1b_control        - Value to be written to PM1B control
 *
 * RETURN:      Status
 *
 * DESCRIPTION: Write the PM1 A/B control registers. These registers are
 *              different than than the PM1 A/B status and enable registers
 *              in that different values can be written to the A/B registers.
 *              Most notably, the SLP_TYP bits can be different, as per the
 *              values returned from the _Sx predefined methods.
 *
 ******************************************************************************/

acpi_status acpi_hw_write_pm1_control(u32 pm1a_control, u32 pm1b_control)
{
        acpi_status status;

        ACPI_FUNCTION_TRACE(hw_write_pm1_control);

        status =
            acpi_hw_write(pm1a_control, &acpi_gbl_FADT.xpm1a_control_block);
        if (ACPI_FAILURE(status)) {
                return_ACPI_STATUS(status);
        }

        if (acpi_gbl_FADT.xpm1b_control_block.address) {
                status =
                    acpi_hw_write(pm1b_control,
                                  &acpi_gbl_FADT.xpm1b_control_block);
        }
        return_ACPI_STATUS(status);
}

/******************************************************************************
 *
 * FUNCTION:    acpi_hw_register_read
 *
 * PARAMETERS:  register_id         - ACPI Register ID
 *              return_value        - Where the register value is returned
 *
 * RETURN:      Status and the value read.
 *
 * DESCRIPTION: Read from the specified ACPI register
 *
 ******************************************************************************/
acpi_status acpi_hw_register_read(u32 register_id, u32 *return_value)
{
        u32 value = 0;
        u64 value64;
        acpi_status status;

        ACPI_FUNCTION_TRACE(hw_register_read);

        switch (register_id) {
        case ACPI_REGISTER_PM1_STATUS:  /* PM1 A/B: 16-bit access each */

                status = acpi_hw_read_multiple(&value,
                                               &acpi_gbl_xpm1a_status,
                                               &acpi_gbl_xpm1b_status);
                break;

        case ACPI_REGISTER_PM1_ENABLE:  /* PM1 A/B: 16-bit access each */

                status = acpi_hw_read_multiple(&value,
                                               &acpi_gbl_xpm1a_enable,
                                               &acpi_gbl_xpm1b_enable);
                break;

        case ACPI_REGISTER_PM1_CONTROL: /* PM1 A/B: 16-bit access each */

                status = acpi_hw_read_multiple(&value,
                                               &acpi_gbl_FADT.
                                               xpm1a_control_block,
                                               &acpi_gbl_FADT.
                                               xpm1b_control_block);

                /*
                 * Zero the write-only bits. From the ACPI specification, "Hardware
                 * Write-Only Bits": "Upon reads to registers with write-only bits,
                 * software masks out all write-only bits."
                 */
                value &= ~ACPI_PM1_CONTROL_WRITEONLY_BITS;
                break;

        case ACPI_REGISTER_PM2_CONTROL: /* 8-bit access */

                status =
                    acpi_hw_read(&value64, &acpi_gbl_FADT.xpm2_control_block);
                value = (u32)value64;
                break;

        case ACPI_REGISTER_PM_TIMER:    /* 32-bit access */

                status = acpi_hw_read(&value64, &acpi_gbl_FADT.xpm_timer_block);
                value = (u32)value64;
                break;

        case ACPI_REGISTER_SMI_COMMAND_BLOCK:   /* 8-bit access */

                status =
                    acpi_hw_read_port(acpi_gbl_FADT.smi_command, &value, 8);
                break;

        default:

                ACPI_ERROR((AE_INFO, "Unknown Register ID: 0x%X", register_id));
                status = AE_BAD_PARAMETER;
                break;
        }

        if (ACPI_SUCCESS(status)) {
                *return_value = (u32)value;
        }

        return_ACPI_STATUS(status);
}

/******************************************************************************
 *
 * FUNCTION:    acpi_hw_register_write
 *
 * PARAMETERS:  register_id         - ACPI Register ID
 *              value               - The value to write
 *
 * RETURN:      Status
 *
 * DESCRIPTION: Write to the specified ACPI register
 *
 * NOTE: In accordance with the ACPI specification, this function automatically
 * preserves the value of the following bits, meaning that these bits cannot be
 * changed via this interface:
 *
 * PM1_CONTROL[0] = SCI_EN
 * PM1_CONTROL[9]
 * PM1_STATUS[11]
 *
 * ACPI References:
 * 1) Hardware Ignored Bits: When software writes to a register with ignored
 *      bit fields, it preserves the ignored bit fields
 * 2) SCI_EN: OSPM always preserves this bit position
 *
 ******************************************************************************/

acpi_status acpi_hw_register_write(u32 register_id, u32 value)
{
        acpi_status status;
        u32 read_value;
        u64 read_value64;

        ACPI_FUNCTION_TRACE(hw_register_write);

        switch (register_id) {
        case ACPI_REGISTER_PM1_STATUS:  /* PM1 A/B: 16-bit access each */
                /*
                 * Handle the "ignored" bit in PM1 Status. According to the ACPI
                 * specification, ignored bits are to be preserved when writing.
                 * Normally, this would mean a read/modify/write sequence. However,
                 * preserving a bit in the status register is different. Writing a
                 * one clears the status, and writing a zero preserves the status.
                 * Therefore, we must always write zero to the ignored bit.
                 *
                 * This behavior is clarified in the ACPI 4.0 specification.
                 */
                value &= ~ACPI_PM1_STATUS_PRESERVED_BITS;

                status = acpi_hw_write_multiple(value,
                                                &acpi_gbl_xpm1a_status,
                                                &acpi_gbl_xpm1b_status);
                break;

        case ACPI_REGISTER_PM1_ENABLE:  /* PM1 A/B: 16-bit access each */

                status = acpi_hw_write_multiple(value,
                                                &acpi_gbl_xpm1a_enable,
                                                &acpi_gbl_xpm1b_enable);
                break;

        case ACPI_REGISTER_PM1_CONTROL: /* PM1 A/B: 16-bit access each */
                /*
                 * Perform a read first to preserve certain bits (per ACPI spec)
                 * Note: This includes SCI_EN, we never want to change this bit
                 */
                status = acpi_hw_read_multiple(&read_value,
                                               &acpi_gbl_FADT.
                                               xpm1a_control_block,
                                               &acpi_gbl_FADT.
                                               xpm1b_control_block);
                if (ACPI_FAILURE(status)) {
                        goto exit;
                }

                /* Insert the bits to be preserved */

                ACPI_INSERT_BITS(value, ACPI_PM1_CONTROL_PRESERVED_BITS,
                                 read_value);

                /* Now we can write the data */

                status = acpi_hw_write_multiple(value,
                                                &acpi_gbl_FADT.
                                                xpm1a_control_block,
                                                &acpi_gbl_FADT.
                                                xpm1b_control_block);
                break;

        case ACPI_REGISTER_PM2_CONTROL: /* 8-bit access */
                /*
                 * For control registers, all reserved bits must be preserved,
                 * as per the ACPI spec.
                 */
                status =
                    acpi_hw_read(&read_value64,
                                 &acpi_gbl_FADT.xpm2_control_block);
                if (ACPI_FAILURE(status)) {
                        goto exit;
                }
                read_value = (u32)read_value64;

                /* Insert the bits to be preserved */

                ACPI_INSERT_BITS(value, ACPI_PM2_CONTROL_PRESERVED_BITS,
                                 read_value);

                status =
                    acpi_hw_write(value, &acpi_gbl_FADT.xpm2_control_block);
                break;

        case ACPI_REGISTER_PM_TIMER:    /* 32-bit access */

                status = acpi_hw_write(value, &acpi_gbl_FADT.xpm_timer_block);
                break;

        case ACPI_REGISTER_SMI_COMMAND_BLOCK:   /* 8-bit access */

                /* SMI_CMD is currently always in IO space */

                status =
                    acpi_hw_write_port(acpi_gbl_FADT.smi_command, value, 8);
                break;

        default:

                ACPI_ERROR((AE_INFO, "Unknown Register ID: 0x%X", register_id));
                status = AE_BAD_PARAMETER;
                break;
        }

exit:
        return_ACPI_STATUS(status);
}

/******************************************************************************
 *
 * FUNCTION:    acpi_hw_read_multiple
 *
 * PARAMETERS:  value               - Where the register value is returned
 *              register_a           - First ACPI register (required)
 *              register_b           - Second ACPI register (optional)
 *
 * RETURN:      Status
 *
 * DESCRIPTION: Read from the specified two-part ACPI register (such as PM1 A/B)
 *
 ******************************************************************************/

static acpi_status
acpi_hw_read_multiple(u32 *value,
                      struct acpi_generic_address *register_a,
                      struct acpi_generic_address *register_b)
{
        u32 value_a = 0;
        u32 value_b = 0;
        u64 value64;
        acpi_status status;

        /* The first register is always required */

        status = acpi_hw_read(&value64, register_a);
        if (ACPI_FAILURE(status)) {
                return (status);
        }
        value_a = (u32)value64;

        /* Second register is optional */

        if (register_b->address) {
                status = acpi_hw_read(&value64, register_b);
                if (ACPI_FAILURE(status)) {
                        return (status);
                }
                value_b = (u32)value64;
        }

        /*
         * OR the two return values together. No shifting or masking is necessary,
         * because of how the PM1 registers are defined in the ACPI specification:
         *
         * "Although the bits can be split between the two register blocks (each
         * register block has a unique pointer within the FADT), the bit positions
         * are maintained. The register block with unimplemented bits (that is,
         * those implemented in the other register block) always returns zeros,
         * and writes have no side effects"
         */
        *value = (value_a | value_b);
        return (AE_OK);
}

/******************************************************************************
 *
 * FUNCTION:    acpi_hw_write_multiple
 *
 * PARAMETERS:  value               - The value to write
 *              register_a           - First ACPI register (required)
 *              register_b           - Second ACPI register (optional)
 *
 * RETURN:      Status
 *
 * DESCRIPTION: Write to the specified two-part ACPI register (such as PM1 A/B)
 *
 ******************************************************************************/

static acpi_status
acpi_hw_write_multiple(u32 value,
                       struct acpi_generic_address *register_a,
                       struct acpi_generic_address *register_b)
{
        acpi_status status;

        /* The first register is always required */

        status = acpi_hw_write(value, register_a);
        if (ACPI_FAILURE(status)) {
                return (status);
        }

        /*
         * Second register is optional
         *
         * No bit shifting or clearing is necessary, because of how the PM1
         * registers are defined in the ACPI specification:
         *
         * "Although the bits can be split between the two register blocks (each
         * register block has a unique pointer within the FADT), the bit positions
         * are maintained. The register block with unimplemented bits (that is,
         * those implemented in the other register block) always returns zeros,
         * and writes have no side effects"
         */
        if (register_b->address) {
                status = acpi_hw_write(value, register_b);
        }

        return (status);
}

#endif                          /* !ACPI_REDUCED_HARDWARE */