ACPICA: Update for field unit access

Mostly for access to Generic Serial Bus, but also cleanup
for the other fields.

Signed-off-by: Bob Moore <[e-mail]>
Signed-off-by: Erik Schmauss <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/acpi/acpica/acinterp.h

···
  * exfield - ACPI AML (p-code) execution - field manipulation
  */
 acpi_status
+acpi_ex_get_protocol_buffer_length(u32 protocol_id, u32 *return_length);
+
+acpi_status
 acpi_ex_common_buffer_setup(union acpi_operand_object *obj_desc,
 			    u32 buffer_length, u32 * datum_count);
 

drivers/acpi/acpica/exfield.c

···
 // SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
 /******************************************************************************
  *
- * Module Name: exfield - ACPI AML (p-code) execution - field manipulation
+ * Module Name: exfield - AML execution - field_unit read/write
  *
  * Copyright (C) 2000 - 2018, Intel Corp.
  *
···
 ACPI_MODULE_NAME("exfield")
 
 /* Local prototypes */
-static u32
-acpi_ex_get_serial_access_length(u32 accessor_type, u32 access_length);
+static acpi_status
+acpi_ex_read_serial_bus(union acpi_operand_object *obj_desc,
+			union acpi_operand_object **return_buffer);
+
+static acpi_status
+acpi_ex_write_serial_bus(union acpi_operand_object *source_desc,
+			 union acpi_operand_object *obj_desc,
+			 union acpi_operand_object **return_buffer);
+
+static acpi_status
+acpi_ex_read_gpio(union acpi_operand_object *obj_desc, void *buffer);
+
+static acpi_status
+acpi_ex_write_gpio(union acpi_operand_object *source_desc,
+		   union acpi_operand_object *obj_desc,
+		   union acpi_operand_object **return_buffer);
+
+/*
+ * This table maps the various Attrib protocols to the byte transfer
+ * length. Used for the generic serial bus.
+ */
+#define ACPI_INVALID_PROTOCOL_ID        0x80
+#define ACPI_MAX_PROTOCOL_ID            0x0F
+
+const u8 acpi_protocol_lengths[] = {
+	ACPI_INVALID_PROTOCOL_ID,	/* 0 - reserved */
+	ACPI_INVALID_PROTOCOL_ID,	/* 1 - reserved */
+	0x00,			/* 2 - ATTRIB_QUICK */
+	ACPI_INVALID_PROTOCOL_ID,	/* 3 - reserved */
+	0x01,			/* 4 - ATTRIB_SEND_RECEIVE */
+	ACPI_INVALID_PROTOCOL_ID,	/* 5 - reserved */
+	0x01,			/* 6 - ATTRIB_BYTE */
+	ACPI_INVALID_PROTOCOL_ID,	/* 7 - reserved */
+	0x02,			/* 8 - ATTRIB_WORD */
+	ACPI_INVALID_PROTOCOL_ID,	/* 9 - reserved */
+	0xFF,			/* A - ATTRIB_BLOCK  */
+	0xFF,			/* B - ATTRIB_BYTES */
+	0x02,			/* C - ATTRIB_PROCESS_CALL */
+	0xFF,			/* D - ATTRIB_BLOCK_PROCESS_CALL */
+	0xFF,			/* E - ATTRIB_RAW_BYTES */
+	0xFF			/* F - ATTRIB_RAW_PROCESS_BYTES */
+};
 
 /*******************************************************************************
  *
- * FUNCTION:    acpi_ex_get_serial_access_length
+ * FUNCTION:    acpi_ex_get_protocol_buffer_length
  *
- * PARAMETERS:  accessor_type   - The type of the protocol indicated by region
+ * PARAMETERS:  protocol_id     - The type of the protocol indicated by region
  *                                field access attributes
- *              access_length   - The access length of the region field
+ *              return_length   - Where the protocol byte transfer length is
+ *                                returned
  *
- * RETURN:      Decoded access length
+ * RETURN:      Status and decoded byte transfer length
  *
  * DESCRIPTION: This routine returns the length of the generic_serial_bus
  *              protocol bytes
  *
  ******************************************************************************/
 
-static u32
-acpi_ex_get_serial_access_length(u32 accessor_type, u32 access_length)
+acpi_status
+acpi_ex_get_protocol_buffer_length(u32 protocol_id, u32 *return_length)
 {
-	u32 length;
 
-	switch (accessor_type) {
-	case AML_FIELD_ATTRIB_QUICK:
+	if ((protocol_id > ACPI_MAX_PROTOCOL_ID) ||
+	    (acpi_protocol_lengths[protocol_id] == ACPI_INVALID_PROTOCOL_ID)) {
+		ACPI_ERROR((AE_INFO,
+			    "Invalid Field/AccessAs protocol ID: 0x%4.4X",
+			    protocol_id));
 
-		length = 0;
-		break;
-
-	case AML_FIELD_ATTRIB_SEND_RCV:
-	case AML_FIELD_ATTRIB_BYTE:
-
-		length = 1;
-		break;
-
-	case AML_FIELD_ATTRIB_WORD:
-	case AML_FIELD_ATTRIB_WORD_CALL:
-
-		length = 2;
-		break;
-
-	case AML_FIELD_ATTRIB_MULTIBYTE:
-	case AML_FIELD_ATTRIB_RAW_BYTES:
-
-		length = access_length;
-		break;
-
-	case AML_FIELD_ATTRIB_RAW_PROCESS:
-		/*
-		 * Worst case bidirectional buffer size. This ignores the
-		 * access_length argument to access_as because it is not needed.
-		 * August 2018.
-		 */
-		length = ACPI_MAX_GSBUS_BUFFER_SIZE;
-		break;
-
-	case AML_FIELD_ATTRIB_BLOCK:
-	case AML_FIELD_ATTRIB_BLOCK_CALL:
-	default:
-
-		length = ACPI_GSBUS_BUFFER_SIZE - 2;
-		break;
+		return (AE_AML_PROTOCOL);
 	}
 
-	return (length);
+	*return_length = acpi_protocol_lengths[protocol_id];
+	return (AE_OK);
 }
 
 /*******************************************************************************
···
 {
 	acpi_status status;
 	union acpi_operand_object *buffer_desc;
-	acpi_size length;
 	void *buffer;
-	u32 function;
-	u16 accessor_type;
+	u32 buffer_length;
 
 	ACPI_FUNCTION_TRACE_PTR(ex_read_data_from_field, obj_desc);
 
···
 		    ACPI_ADR_SPACE_GSBUS
 		    || obj_desc->field.region_obj->region.space_id ==
 		    ACPI_ADR_SPACE_IPMI)) {
-		/*
-		 * This is an SMBus, GSBus or IPMI read. We must create a buffer to
-		 * hold the data and then directly access the region handler.
-		 *
-		 * Note: SMBus and GSBus protocol value is passed in upper 16-bits
-		 * of Function
-		 */
-		if (obj_desc->field.region_obj->region.space_id ==
-		    ACPI_ADR_SPACE_SMBUS) {
-			length = ACPI_SMBUS_BUFFER_SIZE;
-			function =
-			    ACPI_READ | (obj_desc->field.attribute << 16);
-		} else if (obj_desc->field.region_obj->region.space_id ==
-			   ACPI_ADR_SPACE_GSBUS) {
-			accessor_type = obj_desc->field.attribute;
-			if (accessor_type == AML_FIELD_ATTRIB_RAW_PROCESS) {
-				ACPI_ERROR((AE_INFO,
-					    "Invalid direct read using bidirectional write-then-read protocol"));
 
-				return_ACPI_STATUS(AE_AML_PROTOCOL);
-			}
+		/* SMBus, GSBus, IPMI serial */
 
-			length =
-			    acpi_ex_get_serial_access_length(accessor_type,
-							     obj_desc->field.
-							     access_length);
-
-			/*
-			 * Add additional 2 bytes for the generic_serial_bus data buffer:
-			 *
-			 *     Status;    (Byte 0 of the data buffer)
-			 *     Length;    (Byte 1 of the data buffer)
-			 *     Data[x-1]: (Bytes 2-x of the arbitrary length data buffer)
-			 */
-			length += 2;
-			function = ACPI_READ | (accessor_type << 16);
-		} else {	/* IPMI */
-
-			length = ACPI_IPMI_BUFFER_SIZE;
-			function = ACPI_READ;
-		}
-
-		buffer_desc = acpi_ut_create_buffer_object(length);
-		if (!buffer_desc) {
-			return_ACPI_STATUS(AE_NO_MEMORY);
-		}
-
-		/* Lock entire transaction if requested */
-
-		acpi_ex_acquire_global_lock(obj_desc->common_field.field_flags);
-
-		/* Call the region handler for the read */
-
-		status = acpi_ex_access_region(obj_desc, 0,
-					       ACPI_CAST_PTR(u64,
-							     buffer_desc->
-							     buffer.pointer),
-					       function);
-
-		acpi_ex_release_global_lock(obj_desc->common_field.field_flags);
-		goto exit;
+		status = acpi_ex_read_serial_bus(obj_desc, ret_buffer_desc);
+		return_ACPI_STATUS(status);
 	}
 
 	/*
···
 	 *
 	 * Note: Field.length is in bits.
 	 */
-	length =
+	buffer_length =
 	    (acpi_size)ACPI_ROUND_BITS_UP_TO_BYTES(obj_desc->field.bit_length);
 
-	if (length > acpi_gbl_integer_byte_width) {
+	if (buffer_length > acpi_gbl_integer_byte_width) {
 
 		/* Field is too large for an Integer, create a Buffer instead */
 
-		buffer_desc = acpi_ut_create_buffer_object(length);
+		buffer_desc = acpi_ut_create_buffer_object(buffer_length);
 		if (!buffer_desc) {
 			return_ACPI_STATUS(AE_NO_MEMORY);
 		}
···
 			return_ACPI_STATUS(AE_NO_MEMORY);
 		}
 
-		length = acpi_gbl_integer_byte_width;
+		buffer_length = acpi_gbl_integer_byte_width;
 		buffer = &buffer_desc->integer.value;
 	}
 
 	if ((obj_desc->common.type == ACPI_TYPE_LOCAL_REGION_FIELD) &&
 	    (obj_desc->field.region_obj->region.space_id ==
 	     ACPI_ADR_SPACE_GPIO)) {
-		/*
-		 * For GPIO (general_purpose_io), the Address will be the bit offset
-		 * from the previous Connection() operator, making it effectively a
-		 * pin number index. The bit_length is the length of the field, which
-		 * is thus the number of pins.
-		 */
-		ACPI_DEBUG_PRINT((ACPI_DB_BFIELD,
-				  "GPIO FieldRead [FROM]:  Pin %u Bits %u\n",
-				  obj_desc->field.pin_number_index,
-				  obj_desc->field.bit_length));
 
-		/* Lock entire transaction if requested */
+		/* General Purpose I/O */
 
-		acpi_ex_acquire_global_lock(obj_desc->common_field.field_flags);
-
-		/* Perform the write */
-
-		status =
-		    acpi_ex_access_region(obj_desc, 0, (u64 *)buffer,
-					  ACPI_READ);
-
-		acpi_ex_release_global_lock(obj_desc->common_field.field_flags);
-		if (ACPI_FAILURE(status)) {
-			acpi_ut_remove_reference(buffer_desc);
-		} else {
-			*ret_buffer_desc = buffer_desc;
-		}
-		return_ACPI_STATUS(status);
+		status = acpi_ex_read_gpio(obj_desc, buffer);
+		goto exit;
 	}
 
 	ACPI_DEBUG_PRINT((ACPI_DB_BFIELD,
 			  "FieldRead [TO]:   Obj %p, Type %X, Buf %p, ByteLen %X\n",
 			  obj_desc, obj_desc->common.type, buffer,
-			  (u32) length));
+			  buffer_length));
 	ACPI_DEBUG_PRINT((ACPI_DB_BFIELD,
 			  "FieldRead [FROM]: BitLen %X, BitOff %X, ByteOff %X\n",
 			  obj_desc->common_field.bit_length,
···
 
 	/* Read from the field */
 
-	status = acpi_ex_extract_from_field(obj_desc, buffer, (u32) length);
+	status = acpi_ex_extract_from_field(obj_desc, buffer, buffer_length);
 	acpi_ex_release_global_lock(obj_desc->common_field.field_flags);
 
 exit:
···
 			    union acpi_operand_object **result_desc)
 {
 	acpi_status status;
-	u32 length;
-	u32 data_length;
+	u32 buffer_length;
 	void *buffer;
-	union acpi_operand_object *buffer_desc;
-	u32 function;
-	u16 accessor_type;
 
 	ACPI_FUNCTION_TRACE_PTR(ex_write_data_to_field, obj_desc);
 
···
 		}
 	} else if ((obj_desc->common.type == ACPI_TYPE_LOCAL_REGION_FIELD) &&
 		   (obj_desc->field.region_obj->region.space_id ==
+		    ACPI_ADR_SPACE_GPIO)) {
+
+		/* General Purpose I/O */
+
+		status = acpi_ex_write_gpio(source_desc, obj_desc, result_desc);
+		return_ACPI_STATUS(status);
+	} else if ((obj_desc->common.type == ACPI_TYPE_LOCAL_REGION_FIELD) &&
+		   (obj_desc->field.region_obj->region.space_id ==
 		    ACPI_ADR_SPACE_SMBUS
 		    || obj_desc->field.region_obj->region.space_id ==
 		    ACPI_ADR_SPACE_GSBUS
 		    || obj_desc->field.region_obj->region.space_id ==
 		    ACPI_ADR_SPACE_IPMI)) {
-		/*
-		 * This is an SMBus, GSBus or IPMI write. We will bypass the entire
-		 * field mechanism and handoff the buffer directly to the handler.
-		 * For these address spaces, the buffer is bi-directional; on a
-		 * write, return data is returned in the same buffer.
-		 *
-		 * Source must be a buffer of sufficient size:
-		 * ACPI_SMBUS_BUFFER_SIZE, ACPI_GSBUS_BUFFER_SIZE, or
-		 * ACPI_IPMI_BUFFER_SIZE.
-		 *
-		 * Note: SMBus and GSBus protocol type is passed in upper 16-bits
-		 * of Function
-		 */
-		if (source_desc->common.type != ACPI_TYPE_BUFFER) {
-			ACPI_ERROR((AE_INFO,
-				    "SMBus/IPMI/GenericSerialBus write requires "
-				    "Buffer, found type %s",
-				    acpi_ut_get_object_type_name(source_desc)));
 
-			return_ACPI_STATUS(AE_AML_OPERAND_TYPE);
-		}
-
-		if (obj_desc->field.region_obj->region.space_id ==
-		    ACPI_ADR_SPACE_SMBUS) {
-			length = ACPI_SMBUS_BUFFER_SIZE;
-			data_length = length;
-			function =
-			    ACPI_WRITE | (obj_desc->field.attribute << 16);
-		} else if (obj_desc->field.region_obj->region.space_id ==
-			   ACPI_ADR_SPACE_GSBUS) {
-			accessor_type = obj_desc->field.attribute;
-			length =
-			    acpi_ex_get_serial_access_length(accessor_type,
-							     obj_desc->field.
-							     access_length);
-
-			/*
-			 * Buffer format for Generic Serial Bus protocols:
-			 *     Status;    (Byte 0 of the data buffer)
-			 *     Length;    (Byte 1 of the data buffer)
-			 *     Data[x-1]: (Bytes 2-x of the arbitrary length data buffer)
-			 */
-			data_length = source_desc->buffer.pointer[1];	/* Data length is 2nd byte */
-			if (!data_length) {
-				ACPI_ERROR((AE_INFO,
-					    "Invalid zero data length in transfer buffer"));
-
-				return_ACPI_STATUS(AE_AML_BUFFER_LENGTH);
-			}
-
-			function = ACPI_WRITE | (accessor_type << 16);
-		} else {	/* IPMI */
-
-			length = ACPI_IPMI_BUFFER_SIZE;
-			data_length = length;
-			function = ACPI_WRITE;
-		}
-
-		if (source_desc->buffer.length < data_length) {
-			ACPI_ERROR((AE_INFO,
-				    "SMBus/IPMI/GenericSerialBus write requires "
-				    "Buffer data length %u, found buffer length %u",
-				    data_length, source_desc->buffer.length));
-
-			return_ACPI_STATUS(AE_AML_BUFFER_LIMIT);
-		}
-
-		/* Create the transfer/bidirectional buffer */
-
-		buffer_desc = acpi_ut_create_buffer_object(length);
-		if (!buffer_desc) {
-			return_ACPI_STATUS(AE_NO_MEMORY);
-		}
-
-		/* Copy the input buffer data to the transfer buffer */
-
-		buffer = buffer_desc->buffer.pointer;
-		memcpy(buffer, source_desc->buffer.pointer, data_length);
-
-		/* Lock entire transaction if requested */
-
-		acpi_ex_acquire_global_lock(obj_desc->common_field.field_flags);
-
-		/*
-		 * Perform the write (returns status and perhaps data in the
-		 * same buffer)
-		 */
-		status =
-		    acpi_ex_access_region(obj_desc, 0, (u64 *)buffer, function);
-		acpi_ex_release_global_lock(obj_desc->common_field.field_flags);
-
-		*result_desc = buffer_desc;
-		return_ACPI_STATUS(status);
-	} else if ((obj_desc->common.type == ACPI_TYPE_LOCAL_REGION_FIELD) &&
-		   (obj_desc->field.region_obj->region.space_id ==
-		    ACPI_ADR_SPACE_GPIO)) {
-		/*
-		 * For GPIO (general_purpose_io), we will bypass the entire field
-		 * mechanism and handoff the bit address and bit width directly to
-		 * the handler. The Address will be the bit offset
-		 * from the previous Connection() operator, making it effectively a
-		 * pin number index. The bit_length is the length of the field, which
-		 * is thus the number of pins.
-		 */
-		if (source_desc->common.type != ACPI_TYPE_INTEGER) {
-			return_ACPI_STATUS(AE_AML_OPERAND_TYPE);
-		}
-
-		ACPI_DEBUG_PRINT((ACPI_DB_BFIELD,
-				  "GPIO FieldWrite [FROM]: (%s:%X), Val %.8X  [TO]: Pin %u Bits %u\n",
-				  acpi_ut_get_type_name(source_desc->common.
-							type),
-				  source_desc->common.type,
-				  (u32)source_desc->integer.value,
-				  obj_desc->field.pin_number_index,
-				  obj_desc->field.bit_length));
-
-		buffer = &source_desc->integer.value;
-
-		/* Lock entire transaction if requested */
-
-		acpi_ex_acquire_global_lock(obj_desc->common_field.field_flags);
-
-		/* Perform the write */
+		/* SMBus, GSBus, IPMI serial */
 
 		status =
-		    acpi_ex_access_region(obj_desc, 0, (u64 *)buffer,
-					  ACPI_WRITE);
-		acpi_ex_release_global_lock(obj_desc->common_field.field_flags);
+		    acpi_ex_write_serial_bus(source_desc, obj_desc,
+					     result_desc);
 		return_ACPI_STATUS(status);
 	}
 
···
 	case ACPI_TYPE_INTEGER:
 
 		buffer = &source_desc->integer.value;
-		length = sizeof(source_desc->integer.value);
+		buffer_length = sizeof(source_desc->integer.value);
 		break;
 
 	case ACPI_TYPE_BUFFER:
 
 		buffer = source_desc->buffer.pointer;
-		length = source_desc->buffer.length;
+		buffer_length = source_desc->buffer.length;
 		break;
 
 	case ACPI_TYPE_STRING:
 
 		buffer = source_desc->string.pointer;
-		length = source_desc->string.length;
+		buffer_length = source_desc->string.length;
 		break;
 
 	default:
-
 		return_ACPI_STATUS(AE_AML_OPERAND_TYPE);
 	}
 
···
 			  "FieldWrite [FROM]: Obj %p (%s:%X), Buf %p, ByteLen %X\n",
 			  source_desc,
 			  acpi_ut_get_type_name(source_desc->common.type),
-			  source_desc->common.type, buffer, length));
+			  source_desc->common.type, buffer, buffer_length));
 
 	ACPI_DEBUG_PRINT((ACPI_DB_BFIELD,
 			  "FieldWrite [TO]:   Obj %p (%s:%X), BitLen %X, BitOff %X, ByteOff %X\n",
···
 
 	/* Write to the field */
 
-	status = acpi_ex_insert_into_field(obj_desc, buffer, length);
+	status = acpi_ex_insert_into_field(obj_desc, buffer, buffer_length);
+	acpi_ex_release_global_lock(obj_desc->common_field.field_flags);
+	return_ACPI_STATUS(status);
+}
+
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_ex_read_gpio
+ *
+ * PARAMETERS:  obj_desc            - The named field to read
+ *              buffer              - Where the return data is returnd
+ *
+ * RETURN:      Status
+ *
+ * DESCRIPTION: Read from a named field that references a Generic Serial Bus
+ *              field
+ *
+ ******************************************************************************/
+
+static acpi_status
+acpi_ex_read_gpio(union acpi_operand_object *obj_desc, void *buffer)
+{
+	acpi_status status;
+
+	ACPI_FUNCTION_TRACE_PTR(ex_read_gpio, obj_desc);
+
+	/*
+	 * For GPIO (general_purpose_io), the Address will be the bit offset
+	 * from the previous Connection() operator, making it effectively a
+	 * pin number index. The bit_length is the length of the field, which
+	 * is thus the number of pins.
+	 */
+	ACPI_DEBUG_PRINT((ACPI_DB_BFIELD,
+			  "GPIO FieldRead [FROM]:  Pin %u Bits %u\n",
+			  obj_desc->field.pin_number_index,
+			  obj_desc->field.bit_length));
+
+	/* Lock entire transaction if requested */
+
+	acpi_ex_acquire_global_lock(obj_desc->common_field.field_flags);
+
+	/* Perform the read */
+
+	status = acpi_ex_access_region(obj_desc, 0, (u64 *)buffer, ACPI_READ);
+
+	acpi_ex_release_global_lock(obj_desc->common_field.field_flags);
+	return_ACPI_STATUS(status);
+}
+
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_ex_write_gpio
+ *
+ * PARAMETERS:  source_desc         - Contains data to write. Expect to be
+ *                                    an Integer object.
+ *              obj_desc            - The named field
+ *              result_desc         - Where the return value is returned, if any
+ *
+ * RETURN:      Status
+ *
+ * DESCRIPTION: Write to a named field that references a General Purpose I/O
+ *              field.
+ *
+ ******************************************************************************/
+
+static acpi_status
+acpi_ex_write_gpio(union acpi_operand_object *source_desc,
+		   union acpi_operand_object *obj_desc,
+		   union acpi_operand_object **return_buffer)
+{
+	acpi_status status;
+	void *buffer;
+
+	ACPI_FUNCTION_TRACE_PTR(ex_write_gpio, obj_desc);
+
+	/*
+	 * For GPIO (general_purpose_io), we will bypass the entire field
+	 * mechanism and handoff the bit address and bit width directly to
+	 * the handler. The Address will be the bit offset
+	 * from the previous Connection() operator, making it effectively a
+	 * pin number index. The bit_length is the length of the field, which
+	 * is thus the number of pins.
+	 */
+	if (source_desc->common.type != ACPI_TYPE_INTEGER) {
+		return_ACPI_STATUS(AE_AML_OPERAND_TYPE);
+	}
+
+	ACPI_DEBUG_PRINT((ACPI_DB_BFIELD,
+			  "GPIO FieldWrite [FROM]: (%s:%X), Value %.8X  [TO]: Pin %u Bits %u\n",
+			  acpi_ut_get_type_name(source_desc->common.type),
+			  source_desc->common.type,
+			  (u32)source_desc->integer.value,
+			  obj_desc->field.pin_number_index,
+			  obj_desc->field.bit_length));
+
+	buffer = &source_desc->integer.value;
+
+	/* Lock entire transaction if requested */
+
+	acpi_ex_acquire_global_lock(obj_desc->common_field.field_flags);
+
+	/* Perform the write */
+
+	status = acpi_ex_access_region(obj_desc, 0, (u64 *)buffer, ACPI_WRITE);
+	acpi_ex_release_global_lock(obj_desc->common_field.field_flags);
+	return_ACPI_STATUS(status);
+}
+
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_ex_read_serial_bus
+ *
+ * PARAMETERS:  obj_desc            - The named field to read
+ *              return_buffer       - Where the return value is returned, if any
+ *
+ * RETURN:      Status
+ *
+ * DESCRIPTION: Read from a named field that references a serial bus
+ *              (SMBus, IPMI, or GSBus).
+ *
+ ******************************************************************************/
+
+static acpi_status
+acpi_ex_read_serial_bus(union acpi_operand_object *obj_desc,
+			union acpi_operand_object **return_buffer)
+{
+	acpi_status status;
+	u32 buffer_length;
+	union acpi_operand_object *buffer_desc;
+	u32 function;
+	u16 accessor_type;
+
+	ACPI_FUNCTION_TRACE_PTR(ex_read_serial_bus, obj_desc);
+
+	/*
+	 * This is an SMBus, GSBus or IPMI read. We must create a buffer to
+	 * hold the data and then directly access the region handler.
+	 *
+	 * Note: SMBus and GSBus protocol value is passed in upper 16-bits
+	 * of Function
+	 *
+	 * Common buffer format:
+	 *     Status;    (Byte 0 of the data buffer)
+	 *     Length;    (Byte 1 of the data buffer)
+	 *     Data[x-1]: (Bytes 2-x of the arbitrary length data buffer)
+	 */
+	switch (obj_desc->field.region_obj->region.space_id) {
+	case ACPI_ADR_SPACE_SMBUS:
+
+		buffer_length = ACPI_SMBUS_BUFFER_SIZE;
+		function = ACPI_READ | (obj_desc->field.attribute << 16);
+		break;
+
+	case ACPI_ADR_SPACE_IPMI:
+
+		buffer_length = ACPI_IPMI_BUFFER_SIZE;
+		function = ACPI_READ;
+		break;
+
+	case ACPI_ADR_SPACE_GSBUS:
+
+		accessor_type = obj_desc->field.attribute;
+		if (accessor_type == AML_FIELD_ATTRIB_RAW_PROCESS_BYTES) {
+			ACPI_ERROR((AE_INFO,
+				    "Invalid direct read using bidirectional write-then-read protocol"));
+
+			return_ACPI_STATUS(AE_AML_PROTOCOL);
+		}
+
+		status =
+		    acpi_ex_get_protocol_buffer_length(accessor_type,
+						       &buffer_length);
+		if (ACPI_FAILURE(status)) {
+			ACPI_ERROR((AE_INFO,
+				    "Invalid protocol ID for GSBus: 0x%4.4X",
+				    accessor_type));
+
+			return_ACPI_STATUS(status);
+		}
+
+		/* Add header length to get the full size of the buffer */
+
+		buffer_length += ACPI_SERIAL_HEADER_SIZE;
+		function = ACPI_READ | (accessor_type << 16);
+		break;
+
+	default:
+		return_ACPI_STATUS(AE_AML_INVALID_SPACE_ID);
+	}
+
+	/* Create the local transfer buffer that is returned to the caller */
+
+	buffer_desc = acpi_ut_create_buffer_object(buffer_length);
+	if (!buffer_desc) {
+		return_ACPI_STATUS(AE_NO_MEMORY);
+	}
+
+	/* Lock entire transaction if requested */
+
+	acpi_ex_acquire_global_lock(obj_desc->common_field.field_flags);
+
+	/* Call the region handler for the write-then-read */
+
+	status = acpi_ex_access_region(obj_desc, 0,
+				       ACPI_CAST_PTR(u64,
+						     buffer_desc->buffer.
+						     pointer), function);
 	acpi_ex_release_global_lock(obj_desc->common_field.field_flags);
 
+	*return_buffer = buffer_desc;
+	return_ACPI_STATUS(status);
+}
+
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_ex_write_serial_bus
+ *
+ * PARAMETERS:  source_desc         - Contains data to write
+ *              obj_desc            - The named field
+ *              return_buffer       - Where the return value is returned, if any
+ *
+ * RETURN:      Status
+ *
+ * DESCRIPTION: Write to a named field that references a serial bus
+ *              (SMBus, IPMI, GSBus).
+ *
+ ******************************************************************************/
+
+static acpi_status
+acpi_ex_write_serial_bus(union acpi_operand_object *source_desc,
+			 union acpi_operand_object *obj_desc,
+			 union acpi_operand_object **return_buffer)
+{
+	acpi_status status;
+	u32 buffer_length;
+	u32 data_length;
+	void *buffer;
+	union acpi_operand_object *buffer_desc;
+	u32 function;
+	u16 accessor_type;
+
+	ACPI_FUNCTION_TRACE_PTR(ex_write_serial_bus, obj_desc);
+
+	/*
+	 * This is an SMBus, GSBus or IPMI write. We will bypass the entire
+	 * field mechanism and handoff the buffer directly to the handler.
+	 * For these address spaces, the buffer is bidirectional; on a
+	 * write, return data is returned in the same buffer.
+	 *
+	 * Source must be a buffer of sufficient size, these are fixed size:
+	 * ACPI_SMBUS_BUFFER_SIZE, or ACPI_IPMI_BUFFER_SIZE.
+	 *
+	 * Note: SMBus and GSBus protocol type is passed in upper 16-bits
+	 * of Function
+	 *
+	 * Common buffer format:
+	 *     Status;    (Byte 0 of the data buffer)
+	 *     Length;    (Byte 1 of the data buffer)
+	 *     Data[x-1]: (Bytes 2-x of the arbitrary length data buffer)
+	 */
+	if (source_desc->common.type != ACPI_TYPE_BUFFER) {
+		ACPI_ERROR((AE_INFO,
+			    "SMBus/IPMI/GenericSerialBus write requires "
+			    "Buffer, found type %s",
+			    acpi_ut_get_object_type_name(source_desc)));
+
+		return_ACPI_STATUS(AE_AML_OPERAND_TYPE);
+	}
+
+	switch (obj_desc->field.region_obj->region.space_id) {
+	case ACPI_ADR_SPACE_SMBUS:
+
+		buffer_length = ACPI_SMBUS_BUFFER_SIZE;
+		data_length = ACPI_SMBUS_DATA_SIZE;
+		function = ACPI_WRITE | (obj_desc->field.attribute << 16);
+		break;
+
+	case ACPI_ADR_SPACE_IPMI:
+
+		buffer_length = ACPI_IPMI_BUFFER_SIZE;
+		data_length = ACPI_IPMI_DATA_SIZE;
+		function = ACPI_WRITE;
+		break;
+
+	case ACPI_ADR_SPACE_GSBUS:
+
+		accessor_type = obj_desc->field.attribute;
+		status =
+		    acpi_ex_get_protocol_buffer_length(accessor_type,
+						       &buffer_length);
+		if (ACPI_FAILURE(status)) {
+			ACPI_ERROR((AE_INFO,
+				    "Invalid protocol ID for GSBus: 0x%4.4X",
+				    accessor_type));
+
+			return_ACPI_STATUS(status);
+		}
+
+		/* Add header length to get the full size of the buffer */
+
+		buffer_length += ACPI_SERIAL_HEADER_SIZE;
+		data_length = source_desc->buffer.pointer[1];
+		function = ACPI_WRITE | (accessor_type << 16);
+		break;
+
+	default:
+		return_ACPI_STATUS(AE_AML_INVALID_SPACE_ID);
+	}
+
+#if 0
+	OBSOLETE ?
+	    /* Check for possible buffer overflow */
+	    if (data_length > source_desc->buffer.length) {
+		ACPI_ERROR((AE_INFO,
+			    "Length in buffer header (%u)(%u) is greater than "
+			    "the physical buffer length (%u) and will overflow",
+			    data_length, buffer_length,
+			    source_desc->buffer.length));
+
+		return_ACPI_STATUS(AE_AML_BUFFER_LIMIT);
+	}
+#endif
+
+	/* Create the transfer/bidirectional/return buffer */
+
+	buffer_desc = acpi_ut_create_buffer_object(buffer_length);
+	if (!buffer_desc) {
+		return_ACPI_STATUS(AE_NO_MEMORY);
+	}
+
+	/* Copy the input buffer data to the transfer buffer */
+
+	buffer = buffer_desc->buffer.pointer;
+	memcpy(buffer, source_desc->buffer.pointer, data_length);
+
+	/* Lock entire transaction if requested */
+
+	acpi_ex_acquire_global_lock(obj_desc->common_field.field_flags);
+
+	/*
+	 * Perform the write (returns status and perhaps data in the
+	 * same buffer)
+	 */
+	status = acpi_ex_access_region(obj_desc, 0, (u64 *)buffer, function);
+	acpi_ex_release_global_lock(obj_desc->common_field.field_flags);
+
+	*return_buffer = buffer_desc;
 	return_ACPI_STATUS(status);
 }

include/acpi/acconfig.h

···
 #define ACPI_RSDP_CHECKSUM_LENGTH       20
 #define ACPI_RSDP_XCHECKSUM_LENGTH      36
 
-/* SMBus, GSBus and IPMI bidirectional buffer size */
+/*
+ * SMBus, GSBus and IPMI buffer sizes. All have a 2-byte header,
+ * containing both Status and Length.
+ */
+#define ACPI_SERIAL_HEADER_SIZE         2	/* Common for below. Status and Length fields */
 
-#define ACPI_SMBUS_BUFFER_SIZE          34
-#define ACPI_IPMI_BUFFER_SIZE           66
-#define ACPI_GSBUS_BUFFER_SIZE          34	/* Not clear if this is needed */
-#define ACPI_MAX_GSBUS_BUFFER_SIZE      255	/* Worst-case bidirectional buffer */
+#define ACPI_SMBUS_DATA_SIZE            32
+#define ACPI_SMBUS_BUFFER_SIZE          ACPI_SERIAL_HEADER_SIZE + ACPI_SMBUS_DATA_SIZE
+
+#define ACPI_IPMI_DATA_SIZE             64
+#define ACPI_IPMI_BUFFER_SIZE           ACPI_SERIAL_HEADER_SIZE + ACPI_IPMI_DATA_SIZE
+
+#define ACPI_MAX_GSBUS_DATA_SIZE        255
+#define ACPI_MAX_GSBUS_BUFFER_SIZE      ACPI_SERIAL_HEADER_SIZE + ACPI_MAX_GSBUS_DATA_SIZE
 
 /* _sx_d and _sx_w control methods */