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ACPICA: Add support for complex _PLD buffers.

Browse source 
_PLD (Physical Location of Device) returns a bit-packed buffer that
is difficult to parse. This change adds a new interface,
AcpiDecodePldBuffer that parses the buffer into a more usable
local struct. Also adds macros to both get and set individual
fields within the packed _PLD buffer. Adds a new include file,
acbuffer.h - which will be expanded to add structs for other
ACPI names that return buffers. ACPICA BZ 954.

Emit (in comments) the decoded contents of a static _PLD buffer
in order to improve comprehension of this bit-packed buffer.

Add multi-endian support to the _PLD decode routine. Deploy the
multi-endian macros to extract data from the _PLD buffer.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
This commit is contained in:
Bob Moore 2012-08-17 13:07:54 +08:00 committed by Len Brown
parent 4e2f9c278a
commit be030a5768
10 changed files with 360 additions and 24 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

22
drivers/acpi/acpica/aclocal.h
View file

@ -707,15 +707,18 @@ union acpi_parse_value {
u8 disasm_opcode; /* Subtype used for disassembly */\
char aml_op_name[16]) /* Op name (debug only) */
#define ACPI_DASM_BUFFER 0x00
#define ACPI_DASM_RESOURCE 0x01
#define ACPI_DASM_STRING 0x02
#define ACPI_DASM_UNICODE 0x03
#define ACPI_DASM_EISAID 0x04
#define ACPI_DASM_MATCHOP 0x05
#define ACPI_DASM_LNOT_PREFIX 0x06
#define ACPI_DASM_LNOT_SUFFIX 0x07
#define ACPI_DASM_IGNORE 0x08
/* Flags for disasm_flags field above */
#define ACPI_DASM_BUFFER 0x00 /* Buffer is a simple data buffer */
#define ACPI_DASM_RESOURCE 0x01 /* Buffer is a Resource Descriptor */
#define ACPI_DASM_STRING 0x02 /* Buffer is a ASCII string */
#define ACPI_DASM_UNICODE 0x03 /* Buffer is a Unicode string */
#define ACPI_DASM_PLD_METHOD 0x04 /* Buffer is a _PLD method bit-packed buffer */
#define ACPI_DASM_EISAID 0x05 /* Integer is an EISAID */
#define ACPI_DASM_MATCHOP 0x06 /* Parent opcode is a Match() operator */
#define ACPI_DASM_LNOT_PREFIX 0x07 /* Start of a Lnot_equal (etc.) pair of opcodes */
#define ACPI_DASM_LNOT_SUFFIX 0x08 /* End of a Lnot_equal (etc.) pair of opcodes */
#define ACPI_DASM_IGNORE 0x09 /* Not used at this time */
/*
* Generic operation (for example: If, While, Store)
@ -1025,6 +1028,7 @@ struct acpi_port_info {
****************************************************************************/
struct acpi_db_method_info {
acpi_handle method;
acpi_handle main_thread_gate;
acpi_handle thread_complete_gate;
acpi_thread_id *threads;

29
drivers/acpi/acpica/acmacros.h
View file

@ -277,10 +277,33 @@
/* Bitfields within ACPI registers */
#define ACPI_REGISTER_PREPARE_BITS(val, pos, mask) ((val << pos) & mask)
#define ACPI_REGISTER_INSERT_VALUE(reg, pos, mask, val) reg = (reg & (~(mask))) | ACPI_REGISTER_PREPARE_BITS(val, pos, mask)
#define ACPI_REGISTER_PREPARE_BITS(val, pos, mask) \
((val << pos) & mask)
#define ACPI_INSERT_BITS(target, mask, source) target = ((target & (~(mask))) | (source & mask))
#define ACPI_REGISTER_INSERT_VALUE(reg, pos, mask, val) \
reg = (reg & (~(mask))) | ACPI_REGISTER_PREPARE_BITS(val, pos, mask)
#define ACPI_INSERT_BITS(target, mask, source) \
target = ((target & (~(mask))) | (source & mask))
/* Generic bitfield macros and masks */
#define ACPI_GET_BITS(source_ptr, position, mask) \
((*source_ptr >> position) & mask)
#define ACPI_SET_BITS(target_ptr, position, mask, value) \
(*target_ptr |= ((value & mask) << position))
#define ACPI_1BIT_MASK 0x00000001
#define ACPI_2BIT_MASK 0x00000003
#define ACPI_3BIT_MASK 0x00000007
#define ACPI_4BIT_MASK 0x0000000F
#define ACPI_5BIT_MASK 0x0000001F
#define ACPI_6BIT_MASK 0x0000003F
#define ACPI_7BIT_MASK 0x0000007F
#define ACPI_8BIT_MASK 0x000000FF
#define ACPI_16BIT_MASK 0x0000FFFF
#define ACPI_24BIT_MASK 0x00FFFFFF
/*
* An object of type struct acpi_namespace_node can appear in some contexts

87
drivers/acpi/acpica/utxface.c
View file

@ -418,3 +418,90 @@ acpi_check_address_range(acpi_adr_space_type space_id,
ACPI_EXPORT_SYMBOL(acpi_check_address_range)
#endif /* !ACPI_ASL_COMPILER */
/*******************************************************************************
*
* FUNCTION: acpi_decode_pld_buffer
*
* PARAMETERS: in_buffer - Buffer returned by _PLD method
* length - Length of the in_buffer
* return_buffer - Where the decode buffer is returned
*
* RETURN: Status and the decoded _PLD buffer. User must deallocate
* the buffer via ACPI_FREE.
*
* DESCRIPTION: Decode the bit-packed buffer returned by the _PLD method into
* a local struct that is much more useful to an ACPI driver.
*
******************************************************************************/
acpi_status
acpi_decode_pld_buffer(u8 *in_buffer,
acpi_size length, struct acpi_pld_info ** return_buffer)
{
struct acpi_pld_info *pld_info;
u32 *buffer = ACPI_CAST_PTR(u32, in_buffer);
u32 dword;
/* Parameter validation */
if (!in_buffer || !return_buffer || (length < 16)) {
return (AE_BAD_PARAMETER);
}
pld_info = ACPI_ALLOCATE_ZEROED(sizeof(struct acpi_pld_info));
if (!pld_info) {
return (AE_NO_MEMORY);
}
/* First 32-bit DWord */
ACPI_MOVE_32_TO_32(&dword, &buffer[0]);
pld_info->revision = ACPI_PLD_GET_REVISION(&dword);
pld_info->ignore_color = ACPI_PLD_GET_IGNORE_COLOR(&dword);
pld_info->color = ACPI_PLD_GET_COLOR(&dword);
/* Second 32-bit DWord */
ACPI_MOVE_32_TO_32(&dword, &buffer[1]);
pld_info->width = ACPI_PLD_GET_WIDTH(&dword);
pld_info->height = ACPI_PLD_GET_HEIGHT(&dword);
/* Third 32-bit DWord */
ACPI_MOVE_32_TO_32(&dword, &buffer[2]);
pld_info->user_visible = ACPI_PLD_GET_USER_VISIBLE(&dword);
pld_info->dock = ACPI_PLD_GET_DOCK(&dword);
pld_info->lid = ACPI_PLD_GET_LID(&dword);
pld_info->panel = ACPI_PLD_GET_PANEL(&dword);
pld_info->vertical_position = ACPI_PLD_GET_VERTICAL(&dword);
pld_info->horizontal_position = ACPI_PLD_GET_HORIZONTAL(&dword);
pld_info->shape = ACPI_PLD_GET_SHAPE(&dword);
pld_info->group_orientation = ACPI_PLD_GET_ORIENTATION(&dword);
pld_info->group_token = ACPI_PLD_GET_TOKEN(&dword);
pld_info->group_position = ACPI_PLD_GET_POSITION(&dword);
pld_info->bay = ACPI_PLD_GET_BAY(&dword);
/* Fourth 32-bit DWord */
ACPI_MOVE_32_TO_32(&dword, &buffer[3]);
pld_info->ejectable = ACPI_PLD_GET_EJECTABLE(&dword);
pld_info->ospm_eject_required = ACPI_PLD_GET_OSPM_EJECT(&dword);
pld_info->cabinet_number = ACPI_PLD_GET_CABINET(&dword);
pld_info->card_cage_number = ACPI_PLD_GET_CARD_CAGE(&dword);
pld_info->reference = ACPI_PLD_GET_REFERENCE(&dword);
pld_info->rotation = ACPI_PLD_GET_ROTATION(&dword);
pld_info->order = ACPI_PLD_GET_ORDER(&dword);
if (length >= ACPI_PLD_BUFFER_SIZE) {
/* Fifth 32-bit DWord (Revision 2 of _PLD) */
ACPI_MOVE_32_TO_32(&dword, &buffer[4]);
pld_info->vertical_offset = ACPI_PLD_GET_VERT_OFFSET(&dword);
pld_info->horizontal_offset = ACPI_PLD_GET_HORIZ_OFFSET(&dword);
}
*return_buffer = pld_info;
return (AE_OK);
}
ACPI_EXPORT_SYMBOL(acpi_decode_pld_buffer)

192
include/acpi/acbuffer.h Normal file
View file

@ -0,0 +1,192 @@
/******************************************************************************
*
* Name: acbuffer.h - Support for buffers returned by ACPI predefined names
*
*****************************************************************************/
/*
* Copyright (C) 2000 - 2012, 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.
*/
#ifndef __ACBUFFER_H__
#define __ACBUFFER_H__
/*
* Note: C bitfields are not used for this reason:
*
* "Bitfields are great and easy to read, but unfortunately the C language
* does not specify the layout of bitfields in memory, which means they are
* essentially useless for dealing with packed data in on-disk formats or
* binary wire protocols." (Or ACPI tables and buffers.) "If you ask me,
* this decision was a design error in C. Ritchie could have picked an order
* and stuck with it." Norman Ramsey.
* See http://stackoverflow.com/a/1053662/41661
*/
/*
* Formatted _PLD return value. The minimum size is a package containing
* one buffer.
* Revision 1: Buffer is 16 bytes (128 bits)
* Revision 2: Buffer is 20 bytes (160 bits)
*
* Note: This structure is returned from the acpi_decode_pld_buffer
* interface.
*/
struct acpi_pld_info {
u8 revision;
u8 ignore_color;
u32 color;
u16 width;
u16 height;
u8 user_visible;
u8 dock;
u8 lid;
u8 panel;
u8 vertical_position;
u8 horizontal_position;
u8 shape;
u8 group_orientation;
u8 group_token;
u8 group_position;
u8 bay;
u8 ejectable;
u8 ospm_eject_required;
u8 cabinet_number;
u8 card_cage_number;
u8 reference;
u8 rotation;
u8 order;
u8 reserved;
u16 vertical_offset;
u16 horizontal_offset;
};
/*
* Macros to:
* 1) Convert a _PLD buffer to internal struct acpi_pld_info format - ACPI_PLD_GET*
* (Used by acpi_decode_pld_buffer)
* 2) Construct a _PLD buffer - ACPI_PLD_SET*
* (Intended for BIOS use only)
*/
#define ACPI_PLD_REV1_BUFFER_SIZE 16 /* For Revision 1 of the buffer (From ACPI spec) */
#define ACPI_PLD_BUFFER_SIZE 20 /* For Revision 2 of the buffer (From ACPI spec) */
/* First 32-bit dword, bits 0:32 */
#define ACPI_PLD_GET_REVISION(dword) ACPI_GET_BITS (dword, 0, ACPI_7BIT_MASK)
#define ACPI_PLD_SET_REVISION(dword,value) ACPI_SET_BITS (dword, 0, ACPI_7BIT_MASK, value) /* Offset 0, Len 7 */
#define ACPI_PLD_GET_IGNORE_COLOR(dword) ACPI_GET_BITS (dword, 7, ACPI_1BIT_MASK)
#define ACPI_PLD_SET_IGNORE_COLOR(dword,value) ACPI_SET_BITS (dword, 7, ACPI_1BIT_MASK, value) /* Offset 7, Len 1 */
#define ACPI_PLD_GET_COLOR(dword) ACPI_GET_BITS (dword, 8, ACPI_24BIT_MASK)
#define ACPI_PLD_SET_COLOR(dword,value) ACPI_SET_BITS (dword, 8, ACPI_24BIT_MASK, value) /* Offset 8, Len 24 */
/* Second 32-bit dword, bits 33:63 */
#define ACPI_PLD_GET_WIDTH(dword) ACPI_GET_BITS (dword, 0, ACPI_16BIT_MASK)
#define ACPI_PLD_SET_WIDTH(dword,value) ACPI_SET_BITS (dword, 0, ACPI_16BIT_MASK, value) /* Offset 32+0=32, Len 16 */
#define ACPI_PLD_GET_HEIGHT(dword) ACPI_GET_BITS (dword, 16, ACPI_16BIT_MASK)
#define ACPI_PLD_SET_HEIGHT(dword,value) ACPI_SET_BITS (dword, 16, ACPI_16BIT_MASK, value) /* Offset 32+16=48, Len 16 */
/* Third 32-bit dword, bits 64:95 */
#define ACPI_PLD_GET_USER_VISIBLE(dword) ACPI_GET_BITS (dword, 0, ACPI_1BIT_MASK)
#define ACPI_PLD_SET_USER_VISIBLE(dword,value) ACPI_SET_BITS (dword, 0, ACPI_1BIT_MASK, value) /* Offset 64+0=64, Len 1 */
#define ACPI_PLD_GET_DOCK(dword) ACPI_GET_BITS (dword, 1, ACPI_1BIT_MASK)
#define ACPI_PLD_SET_DOCK(dword,value) ACPI_SET_BITS (dword, 1, ACPI_1BIT_MASK, value) /* Offset 64+1=65, Len 1 */
#define ACPI_PLD_GET_LID(dword) ACPI_GET_BITS (dword, 2, ACPI_1BIT_MASK)
#define ACPI_PLD_SET_LID(dword,value) ACPI_SET_BITS (dword, 2, ACPI_1BIT_MASK, value) /* Offset 64+2=66, Len 1 */
#define ACPI_PLD_GET_PANEL(dword) ACPI_GET_BITS (dword, 3, ACPI_3BIT_MASK)
#define ACPI_PLD_SET_PANEL(dword,value) ACPI_SET_BITS (dword, 3, ACPI_3BIT_MASK, value) /* Offset 64+3=67, Len 3 */
#define ACPI_PLD_GET_VERTICAL(dword) ACPI_GET_BITS (dword, 6, ACPI_2BIT_MASK)
#define ACPI_PLD_SET_VERTICAL(dword,value) ACPI_SET_BITS (dword, 6, ACPI_2BIT_MASK, value) /* Offset 64+6=70, Len 2 */
#define ACPI_PLD_GET_HORIZONTAL(dword) ACPI_GET_BITS (dword, 8, ACPI_2BIT_MASK)
#define ACPI_PLD_SET_HORIZONTAL(dword,value) ACPI_SET_BITS (dword, 8, ACPI_2BIT_MASK, value) /* Offset 64+8=72, Len 2 */
#define ACPI_PLD_GET_SHAPE(dword) ACPI_GET_BITS (dword, 10, ACPI_4BIT_MASK)
#define ACPI_PLD_SET_SHAPE(dword,value) ACPI_SET_BITS (dword, 10, ACPI_4BIT_MASK, value) /* Offset 64+10=74, Len 4 */
#define ACPI_PLD_GET_ORIENTATION(dword) ACPI_GET_BITS (dword, 14, ACPI_1BIT_MASK)
#define ACPI_PLD_SET_ORIENTATION(dword,value) ACPI_SET_BITS (dword, 14, ACPI_1BIT_MASK, value) /* Offset 64+14=78, Len 1 */
#define ACPI_PLD_GET_TOKEN(dword) ACPI_GET_BITS (dword, 15, ACPI_8BIT_MASK)
#define ACPI_PLD_SET_TOKEN(dword,value) ACPI_SET_BITS (dword, 15, ACPI_8BIT_MASK, value) /* Offset 64+15=79, Len 8 */
#define ACPI_PLD_GET_POSITION(dword) ACPI_GET_BITS (dword, 23, ACPI_8BIT_MASK)
#define ACPI_PLD_SET_POSITION(dword,value) ACPI_SET_BITS (dword, 23, ACPI_8BIT_MASK, value) /* Offset 64+23=87, Len 8 */
#define ACPI_PLD_GET_BAY(dword) ACPI_GET_BITS (dword, 31, ACPI_1BIT_MASK)
#define ACPI_PLD_SET_BAY(dword,value) ACPI_SET_BITS (dword, 31, ACPI_1BIT_MASK, value) /* Offset 64+31=95, Len 1 */
/* Fourth 32-bit dword, bits 96:127 */
#define ACPI_PLD_GET_EJECTABLE(dword) ACPI_GET_BITS (dword, 0, ACPI_1BIT_MASK)
#define ACPI_PLD_SET_EJECTABLE(dword,value) ACPI_SET_BITS (dword, 0, ACPI_1BIT_MASK, value) /* Offset 96+0=96, Len 1 */
#define ACPI_PLD_GET_OSPM_EJECT(dword) ACPI_GET_BITS (dword, 1, ACPI_1BIT_MASK)
#define ACPI_PLD_SET_OSPM_EJECT(dword,value) ACPI_SET_BITS (dword, 1, ACPI_1BIT_MASK, value) /* Offset 96+1=97, Len 1 */
#define ACPI_PLD_GET_CABINET(dword) ACPI_GET_BITS (dword, 2, ACPI_8BIT_MASK)
#define ACPI_PLD_SET_CABINET(dword,value) ACPI_SET_BITS (dword, 2, ACPI_8BIT_MASK, value) /* Offset 96+2=98, Len 8 */
#define ACPI_PLD_GET_CARD_CAGE(dword) ACPI_GET_BITS (dword, 10, ACPI_8BIT_MASK)
#define ACPI_PLD_SET_CARD_CAGE(dword,value) ACPI_SET_BITS (dword, 10, ACPI_8BIT_MASK, value) /* Offset 96+10=106, Len 8 */
#define ACPI_PLD_GET_REFERENCE(dword) ACPI_GET_BITS (dword, 18, ACPI_1BIT_MASK)
#define ACPI_PLD_SET_REFERENCE(dword,value) ACPI_SET_BITS (dword, 18, ACPI_1BIT_MASK, value) /* Offset 96+18=114, Len 1 */
#define ACPI_PLD_GET_ROTATION(dword) ACPI_GET_BITS (dword, 19, ACPI_4BIT_MASK)
#define ACPI_PLD_SET_ROTATION(dword,value) ACPI_SET_BITS (dword, 19, ACPI_4BIT_MASK, value) /* Offset 96+19=115, Len 4 */
#define ACPI_PLD_GET_ORDER(dword) ACPI_GET_BITS (dword, 23, ACPI_5BIT_MASK)
#define ACPI_PLD_SET_ORDER(dword,value) ACPI_SET_BITS (dword, 23, ACPI_5BIT_MASK, value) /* Offset 96+23=119, Len 5 */
/* Fifth 32-bit dword, bits 128:159 (Revision 2 of _PLD only) */
#define ACPI_PLD_GET_VERT_OFFSET(dword) ACPI_GET_BITS (dword, 0, ACPI_16BIT_MASK)
#define ACPI_PLD_SET_VERT_OFFSET(dword,value) ACPI_SET_BITS (dword, 0, ACPI_16BIT_MASK, value) /* Offset 128+0=128, Len 16 */
#define ACPI_PLD_GET_HORIZ_OFFSET(dword) ACPI_GET_BITS (dword, 16, ACPI_16BIT_MASK)
#define ACPI_PLD_SET_HORIZ_OFFSET(dword,value) ACPI_SET_BITS (dword, 16, ACPI_16BIT_MASK, value) /* Offset 128+16=144, Len 16 */
#endif /* ACBUFFER_H */

1
include/acpi/acnames.h
View file

@ -63,6 +63,7 @@
#define METHOD_NAME__PRW "_PRW"
#define METHOD_NAME__SRS "_SRS"
#define METHOD_NAME__CBA "_CBA"
#define METHOD_NAME__PLD "_PLD"
/* Method names - these methods must appear at the namespace root */

5
include/acpi/acpixf.h
View file

@ -52,6 +52,7 @@
#include "acconfig.h"
#include "actypes.h"
#include "actbl.h"
#include "acbuffer.h"
extern u8 acpi_gbl_permanent_mmap;
@ -144,6 +145,10 @@ acpi_check_address_range(acpi_adr_space_type space_id,
acpi_physical_address address,
acpi_size length, u8 warn);
acpi_status
acpi_decode_pld_buffer(u8 *in_buffer,
acpi_size length, struct acpi_pld_info **return_buffer);
/*
* ACPI Memory management
*/

12
include/acpi/actbl.h
View file

@ -79,9 +79,15 @@
#pragma pack(1)
/*
* Note about bitfields: The u8 type is used for bitfields in ACPI tables.
* This is the only type that is even remotely portable. Anything else is not
* portable, so do not use any other bitfield types.
* Note: C bitfields are not used for this reason:
*
* "Bitfields are great and easy to read, but unfortunately the C language
* does not specify the layout of bitfields in memory, which means they are
* essentially useless for dealing with packed data in on-disk formats or
* binary wire protocols." (Or ACPI tables and buffers.) "If you ask me,
* this decision was a design error in C. Ritchie could have picked an order
* and stuck with it." Norman Ramsey.
* See http://stackoverflow.com/a/1053662/41661
*/
/*******************************************************************************

12
include/acpi/actbl1.h
View file

@ -79,9 +79,15 @@
#pragma pack(1)
/*
* Note about bitfields: The u8 type is used for bitfields in ACPI tables.
* This is the only type that is even remotely portable. Anything else is not
* portable, so do not use any other bitfield types.
* Note: C bitfields are not used for this reason:
*
* "Bitfields are great and easy to read, but unfortunately the C language
* does not specify the layout of bitfields in memory, which means they are
* essentially useless for dealing with packed data in on-disk formats or
* binary wire protocols." (Or ACPI tables and buffers.) "If you ask me,
* this decision was a design error in C. Ritchie could have picked an order
* and stuck with it." Norman Ramsey.
* See http://stackoverflow.com/a/1053662/41661
*/
/*******************************************************************************

12
include/acpi/actbl2.h
View file

@ -98,9 +98,15 @@
#pragma pack(1)
/*
* Note about bitfields: The u8 type is used for bitfields in ACPI tables.
* This is the only type that is even remotely portable. Anything else is not
* portable, so do not use any other bitfield types.
* Note: C bitfields are not used for this reason:
*
* "Bitfields are great and easy to read, but unfortunately the C language
* does not specify the layout of bitfields in memory, which means they are
* essentially useless for dealing with packed data in on-disk formats or
* binary wire protocols." (Or ACPI tables and buffers.) "If you ask me,
* this decision was a design error in C. Ritchie could have picked an order
* and stuck with it." Norman Ramsey.
* See http://stackoverflow.com/a/1053662/41661
*/
/*******************************************************************************

12
include/acpi/actbl3.h
View file

@ -86,9 +86,15 @@
#pragma pack(1)
/*
* Note about bitfields: The u8 type is used for bitfields in ACPI tables.
* This is the only type that is even remotely portable. Anything else is not
* portable, so do not use any other bitfield types.
* Note: C bitfields are not used for this reason:
*
* "Bitfields are great and easy to read, but unfortunately the C language
* does not specify the layout of bitfields in memory, which means they are
* essentially useless for dealing with packed data in on-disk formats or
* binary wire protocols." (Or ACPI tables and buffers.) "If you ask me,
* this decision was a design error in C. Ritchie could have picked an order
* and stuck with it." Norman Ramsey.
* See http://stackoverflow.com/a/1053662/41661
*/
/*******************************************************************************