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1 | |
2 | In order to support ACPI open-ended hardware configurations (e.g. development | |
3 | boards) we need a way to augment the ACPI configuration provided by the firmware | |
4 | image. A common example is connecting sensors on I2C / SPI buses on development | |
5 | boards. | |
6 | ||
7 | Although this can be accomplished by creating a kernel platform driver or | |
8 | recompiling the firmware image with updated ACPI tables, neither is practical: | |
9 | the former proliferates board specific kernel code while the latter requires | |
10 | access to firmware tools which are often not publicly available. | |
11 | ||
12 | Because ACPI supports external references in AML code a more practical | |
13 | way to augment firmware ACPI configuration is by dynamically loading | |
14 | user defined SSDT tables that contain the board specific information. | |
15 | ||
16 | For example, to enumerate a Bosch BMA222E accelerometer on the I2C bus of the | |
17 | Minnowboard MAX development board exposed via the LSE connector [1], the | |
18 | following ASL code can be used: | |
19 | ||
20 | DefinitionBlock ("minnowmax.aml", "SSDT", 1, "Vendor", "Accel", 0x00000003) | |
21 | { | |
22 | External (\_SB.I2C6, DeviceObj) | |
23 | ||
24 | Scope (\_SB.I2C6) | |
25 | { | |
26 | Device (STAC) | |
27 | { | |
28 | Name (_ADR, Zero) | |
29 | Name (_HID, "BMA222E") | |
30 | ||
31 | Method (_CRS, 0, Serialized) | |
32 | { | |
33 | Name (RBUF, ResourceTemplate () | |
34 | { | |
35 | I2cSerialBus (0x0018, ControllerInitiated, 0x00061A80, | |
36 | AddressingMode7Bit, "\\_SB.I2C6", 0x00, | |
37 | ResourceConsumer, ,) | |
38 | GpioInt (Edge, ActiveHigh, Exclusive, PullDown, 0x0000, | |
39 | "\\_SB.GPO2", 0x00, ResourceConsumer, , ) | |
40 | { // Pin list | |
41 | 0 | |
42 | } | |
43 | }) | |
44 | Return (RBUF) | |
45 | } | |
46 | } | |
47 | } | |
48 | } | |
49 | ||
50 | which can then be compiled to AML binary format: | |
51 | ||
52 | $ iasl minnowmax.asl | |
53 | ||
54 | Intel ACPI Component Architecture | |
55 | ASL Optimizing Compiler version 20140214-64 [Mar 29 2014] | |
56 | Copyright (c) 2000 - 2014 Intel Corporation | |
57 | ||
58 | ASL Input: minnomax.asl - 30 lines, 614 bytes, 7 keywords | |
59 | AML Output: minnowmax.aml - 165 bytes, 6 named objects, 1 executable opcodes | |
60 | ||
61 | [1] http://wiki.minnowboard.org/MinnowBoard_MAX#Low_Speed_Expansion_Connector_.28Top.29 | |
62 | ||
63 | The resulting AML code can then be loaded by the kernel using one of the methods | |
64 | below. | |
65 | ||
66 | == Loading ACPI SSDTs from initrd == | |
67 | ||
68 | This option allows loading of user defined SSDTs from initrd and it is useful | |
69 | when the system does not support EFI or when there is not enough EFI storage. | |
70 | ||
71 | It works in a similar way with initrd based ACPI tables override/upgrade: SSDT | |
72 | aml code must be placed in the first, uncompressed, initrd under the | |
73 | "kernel/firmware/acpi" path. Multiple files can be used and this will translate | |
74 | in loading multiple tables. Only SSDT and OEM tables are allowed. See | |
75 | initrd_table_override.txt for more details. | |
76 | ||
77 | Here is an example: | |
78 | ||
79 | # Add the raw ACPI tables to an uncompressed cpio archive. | |
80 | # They must be put into a /kernel/firmware/acpi directory inside the | |
81 | # cpio archive. | |
82 | # The uncompressed cpio archive must be the first. | |
83 | # Other, typically compressed cpio archives, must be | |
84 | # concatenated on top of the uncompressed one. | |
85 | mkdir -p kernel/firmware/acpi | |
86 | cp ssdt.aml kernel/firmware/acpi | |
87 | ||
88 | # Create the uncompressed cpio archive and concatenate the original initrd | |
89 | # on top: | |
90 | find kernel | cpio -H newc --create > /boot/instrumented_initrd | |
91 | cat /boot/initrd >>/boot/instrumented_initrd | |
475fb4e8 OP |
92 | |
93 | == Loading ACPI SSDTs from EFI variables == | |
94 | ||
95 | This is the preferred method, when EFI is supported on the platform, because it | |
96 | allows a persistent, OS independent way of storing the user defined SSDTs. There | |
97 | is also work underway to implement EFI support for loading user defined SSDTs | |
98 | and using this method will make it easier to convert to the EFI loading | |
99 | mechanism when that will arrive. | |
100 | ||
101 | In order to load SSDTs from an EFI variable the efivar_ssdt kernel command line | |
102 | parameter can be used. The argument for the option is the variable name to | |
103 | use. If there are multiple variables with the same name but with different | |
104 | vendor GUIDs, all of them will be loaded. | |
105 | ||
106 | In order to store the AML code in an EFI variable the efivarfs filesystem can be | |
107 | used. It is enabled and mounted by default in /sys/firmware/efi/efivars in all | |
108 | recent distribution. | |
109 | ||
110 | Creating a new file in /sys/firmware/efi/efivars will automatically create a new | |
111 | EFI variable. Updating a file in /sys/firmware/efi/efivars will update the EFI | |
112 | variable. Please note that the file name needs to be specially formatted as | |
113 | "Name-GUID" and that the first 4 bytes in the file (little-endian format) | |
114 | represent the attributes of the EFI variable (see EFI_VARIABLE_MASK in | |
115 | include/linux/efi.h). Writing to the file must also be done with one write | |
116 | operation. | |
117 | ||
118 | For example, you can use the following bash script to create/update an EFI | |
119 | variable with the content from a given file: | |
120 | ||
121 | #!/bin/sh -e | |
122 | ||
123 | while ! [ -z "$1" ]; do | |
124 | case "$1" in | |
125 | "-f") filename="$2"; shift;; | |
126 | "-g") guid="$2"; shift;; | |
127 | *) name="$1";; | |
128 | esac | |
129 | shift | |
130 | done | |
131 | ||
132 | usage() | |
133 | { | |
134 | echo "Syntax: ${0##*/} -f filename [ -g guid ] name" | |
135 | exit 1 | |
136 | } | |
137 | ||
138 | [ -n "$name" -a -f "$filename" ] || usage | |
139 | ||
140 | EFIVARFS="/sys/firmware/efi/efivars" | |
141 | ||
142 | [ -d "$EFIVARFS" ] || exit 2 | |
143 | ||
144 | if stat -tf $EFIVARFS | grep -q -v de5e81e4; then | |
145 | mount -t efivarfs none $EFIVARFS | |
146 | fi | |
147 | ||
148 | # try to pick up an existing GUID | |
149 | [ -n "$guid" ] || guid=$(find "$EFIVARFS" -name "$name-*" | head -n1 | cut -f2- -d-) | |
150 | ||
151 | # use a randomly generated GUID | |
152 | [ -n "$guid" ] || guid="$(cat /proc/sys/kernel/random/uuid)" | |
153 | ||
154 | # efivarfs expects all of the data in one write | |
155 | tmp=$(mktemp) | |
156 | /bin/echo -ne "\007\000\000\000" | cat - $filename > $tmp | |
157 | dd if=$tmp of="$EFIVARFS/$name-$guid" bs=$(stat -c %s $tmp) | |
158 | rm $tmp | |
612bd01f OP |
159 | |
160 | == Loading ACPI SSDTs from configfs == | |
161 | ||
162 | This option allows loading of user defined SSDTs from userspace via the configfs | |
163 | interface. The CONFIG_ACPI_CONFIGFS option must be select and configfs must be | |
164 | mounted. In the following examples, we assume that configfs has been mounted in | |
165 | /config. | |
166 | ||
167 | New tables can be loading by creating new directories in /config/acpi/table/ and | |
168 | writing the SSDT aml code in the aml attribute: | |
169 | ||
170 | cd /config/acpi/table | |
171 | mkdir my_ssdt | |
172 | cat ~/ssdt.aml > my_ssdt/aml |