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Diffstat (limited to 'Documentation/acpi/ssdt-overlays.txt')
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diff --git a/Documentation/acpi/ssdt-overlays.txt b/Documentation/acpi/ssdt-overlays.txt deleted file mode 100644 index 5ae13f161ea2..000000000000 --- a/Documentation/acpi/ssdt-overlays.txt +++ /dev/null @@ -1,172 +0,0 @@ - -In order to support ACPI open-ended hardware configurations (e.g. development -boards) we need a way to augment the ACPI configuration provided by the firmware -image. A common example is connecting sensors on I2C / SPI buses on development -boards. - -Although this can be accomplished by creating a kernel platform driver or -recompiling the firmware image with updated ACPI tables, neither is practical: -the former proliferates board specific kernel code while the latter requires -access to firmware tools which are often not publicly available. - -Because ACPI supports external references in AML code a more practical -way to augment firmware ACPI configuration is by dynamically loading -user defined SSDT tables that contain the board specific information. - -For example, to enumerate a Bosch BMA222E accelerometer on the I2C bus of the -Minnowboard MAX development board exposed via the LSE connector [1], the -following ASL code can be used: - -DefinitionBlock ("minnowmax.aml", "SSDT", 1, "Vendor", "Accel", 0x00000003) -{ - External (\_SB.I2C6, DeviceObj) - - Scope (\_SB.I2C6) - { - Device (STAC) - { - Name (_ADR, Zero) - Name (_HID, "BMA222E") - - Method (_CRS, 0, Serialized) - { - Name (RBUF, ResourceTemplate () - { - I2cSerialBus (0x0018, ControllerInitiated, 0x00061A80, - AddressingMode7Bit, "\\_SB.I2C6", 0x00, - ResourceConsumer, ,) - GpioInt (Edge, ActiveHigh, Exclusive, PullDown, 0x0000, - "\\_SB.GPO2", 0x00, ResourceConsumer, , ) - { // Pin list - 0 - } - }) - Return (RBUF) - } - } - } -} - -which can then be compiled to AML binary format: - -$ iasl minnowmax.asl - -Intel ACPI Component Architecture -ASL Optimizing Compiler version 20140214-64 [Mar 29 2014] -Copyright (c) 2000 - 2014 Intel Corporation - -ASL Input: minnomax.asl - 30 lines, 614 bytes, 7 keywords -AML Output: minnowmax.aml - 165 bytes, 6 named objects, 1 executable opcodes - -[1] http://wiki.minnowboard.org/MinnowBoard_MAX#Low_Speed_Expansion_Connector_.28Top.29 - -The resulting AML code can then be loaded by the kernel using one of the methods -below. - -== Loading ACPI SSDTs from initrd == - -This option allows loading of user defined SSDTs from initrd and it is useful -when the system does not support EFI or when there is not enough EFI storage. - -It works in a similar way with initrd based ACPI tables override/upgrade: SSDT -aml code must be placed in the first, uncompressed, initrd under the -"kernel/firmware/acpi" path. Multiple files can be used and this will translate -in loading multiple tables. Only SSDT and OEM tables are allowed. See -initrd_table_override.txt for more details. - -Here is an example: - -# Add the raw ACPI tables to an uncompressed cpio archive. -# They must be put into a /kernel/firmware/acpi directory inside the -# cpio archive. -# The uncompressed cpio archive must be the first. -# Other, typically compressed cpio archives, must be -# concatenated on top of the uncompressed one. -mkdir -p kernel/firmware/acpi -cp ssdt.aml kernel/firmware/acpi - -# Create the uncompressed cpio archive and concatenate the original initrd -# on top: -find kernel | cpio -H newc --create > /boot/instrumented_initrd -cat /boot/initrd >>/boot/instrumented_initrd - -== Loading ACPI SSDTs from EFI variables == - -This is the preferred method, when EFI is supported on the platform, because it -allows a persistent, OS independent way of storing the user defined SSDTs. There -is also work underway to implement EFI support for loading user defined SSDTs -and using this method will make it easier to convert to the EFI loading -mechanism when that will arrive. - -In order to load SSDTs from an EFI variable the efivar_ssdt kernel command line -parameter can be used. The argument for the option is the variable name to -use. If there are multiple variables with the same name but with different -vendor GUIDs, all of them will be loaded. - -In order to store the AML code in an EFI variable the efivarfs filesystem can be -used. It is enabled and mounted by default in /sys/firmware/efi/efivars in all -recent distribution. - -Creating a new file in /sys/firmware/efi/efivars will automatically create a new -EFI variable. Updating a file in /sys/firmware/efi/efivars will update the EFI -variable. Please note that the file name needs to be specially formatted as -"Name-GUID" and that the first 4 bytes in the file (little-endian format) -represent the attributes of the EFI variable (see EFI_VARIABLE_MASK in -include/linux/efi.h). Writing to the file must also be done with one write -operation. - -For example, you can use the following bash script to create/update an EFI -variable with the content from a given file: - -#!/bin/sh -e - -while ! [ -z "$1" ]; do - case "$1" in - "-f") filename="$2"; shift;; - "-g") guid="$2"; shift;; - *) name="$1";; - esac - shift -done - -usage() -{ - echo "Syntax: ${0##*/} -f filename [ -g guid ] name" - exit 1 -} - -[ -n "$name" -a -f "$filename" ] || usage - -EFIVARFS="/sys/firmware/efi/efivars" - -[ -d "$EFIVARFS" ] || exit 2 - -if stat -tf $EFIVARFS | grep -q -v de5e81e4; then - mount -t efivarfs none $EFIVARFS -fi - -# try to pick up an existing GUID -[ -n "$guid" ] || guid=$(find "$EFIVARFS" -name "$name-*" | head -n1 | cut -f2- -d-) - -# use a randomly generated GUID -[ -n "$guid" ] || guid="$(cat /proc/sys/kernel/random/uuid)" - -# efivarfs expects all of the data in one write -tmp=$(mktemp) -/bin/echo -ne "\007\000\000\000" | cat - $filename > $tmp -dd if=$tmp of="$EFIVARFS/$name-$guid" bs=$(stat -c %s $tmp) -rm $tmp - -== Loading ACPI SSDTs from configfs == - -This option allows loading of user defined SSDTs from userspace via the configfs -interface. The CONFIG_ACPI_CONFIGFS option must be select and configfs must be -mounted. In the following examples, we assume that configfs has been mounted in -/config. - -New tables can be loading by creating new directories in /config/acpi/table/ and -writing the SSDT aml code in the aml attribute: - -cd /config/acpi/table -mkdir my_ssdt -cat ~/ssdt.aml > my_ssdt/aml |