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-rw-r--r--drivers/acpi/acpica/hwregs.c802
1 files changed, 802 insertions, 0 deletions
diff --git a/drivers/acpi/acpica/hwregs.c b/drivers/acpi/acpica/hwregs.c
new file mode 100644
index 000000000..f62d5d024
--- /dev/null
+++ b/drivers/acpi/acpica/hwregs.c
@@ -0,0 +1,802 @@
+// SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
+/*******************************************************************************
+ *
+ * Module Name: hwregs - Read/write access functions for the various ACPI
+ * control and status registers.
+ *
+ ******************************************************************************/
+
+#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_raw_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_raw_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 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);
+ if (ACPI_SUCCESS(status)) {
+ value = (u32)value64;
+ }
+ break;
+
+ case ACPI_REGISTER_PM_TIMER: /* 32-bit access */
+
+ status = acpi_hw_read(&value64, &acpi_gbl_FADT.xpm_timer_block);
+ if (ACPI_SUCCESS(status)) {
+ 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 */