mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-21 08:19:28 +00:00
![Andy Shevchenko](/assets/img/avatar_default.png)
This updates the following: 1) The ASL code to follow latest ACPI requirements, i.e. - static buffer to be defined outside of the method - The _ADR and _HID shouldn't be together for the same device 2) EFI section relies on the additional kernel configuration option, i.e. CONFIG_EFI_CUSTOM_SSDT_OVERLAYS 3) Refer to ACPI machine language as AML (capitalized) 4) Miscellaneous amendments Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
181 lines
6.6 KiB
ReStructuredText
181 lines
6.6 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
=============
|
|
SSDT Overlays
|
|
=============
|
|
|
|
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 (_HID, "BMA222E")
|
|
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
|
|
}
|
|
})
|
|
|
|
Method (_CRS, 0, Serialized)
|
|
{
|
|
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] https://www.elinux.org/Minnowboard:MinnowMax#Low_Speed_Expansion_.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. To enable it, the
|
|
CONFIG_EFI_CUSTOM_SSDT_OVERLAYS shoyld be chosen to y.
|
|
|
|
In order to load SSDTs from an EFI variable the ``"efivar_ssdt=..."`` kernel
|
|
command line parameter can be used (the name has a limitation of 16 characters).
|
|
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 [ -n "$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 user space 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
|
|
/sys/kernel/config.
|
|
|
|
New tables can be loading by creating new directories in /sys/kernel/config/acpi/table
|
|
and writing the SSDT AML code in the aml attribute::
|
|
|
|
cd /sys/kernel/config/acpi/table
|
|
mkdir my_ssdt
|
|
cat ~/ssdt.aml > my_ssdt/aml
|