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We can declare platform device information in dts file, rather than hard coding every data into operating system. Taking "arm" architecture as example. it supports dts and we will take dts from arch/arm/boot/dts/xx.dts. Convert this xx.dts into xx.dtb and loaded with kernel Image. I recently came across ACPI, when i came across x86 architecture, from the documents, what i understood is ACPI is similar to device tree. We can declare platform device information information in ACPI tables, my doubt is where exactly these ACPI tables present. How can i load this info to linux. What is the advantage of using ACPI over dts. Please correct me if i am wrong. Thanks in advance
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dtsi files are included files, containing definitions of SoC-level information, while . dts files are final device trees containing board-level information. The . dtsi extension denotes “device tree source include”.
Section 1.3 (Goals) of the UEFI specifications has a list of goals for UEFI. ACPI is a standardized interface to pass information (in the form of tables and bytecode) from the firmware to the OS. Some hardware is not discoverable and the OS could only support it by including a big list of presence-tests and drivers.
Not completely correct:
ACPI was always very limited in scope and depends on firmware, while DT stands on its own (just requires the bootloader to pass the right dtb to the kernel).
ACPI is the unprofessional, hackish attempt of bios and board vendors to solve a small subset of the problems that DT already solved long ago. A major pro argument for those gallows-wearing folks probably is that ACPI/BIOS hides lots of low level configuration stuff (up to runtime device programming, eg. for power management) in the firmware blob, thus preventing the OS kernel to have full control over the machine. (which finally leads to things like broken machines by broken BIOS, etc). We, the kernel developers, often have to work around crappy BIOSes.
My strong advice: get of ACPI when you can.
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Breathe with lungs or gills? Depends on where you live.
A rough classification of architectures is
x86 - Server/PC - ACPI table
ARM - embedded systems - Device Tree
On server/PC motherboards, the ACPI table is a part of the UEFI firmware, which resides on the flash chip. The OS would be installed later somewhere else (hard drive or so). The OS parses the ACPI table, but OS developers don't control what is already written in the firmware; or they don't even know the internal design of the board. The board vendor (firmware provider) needs to support whatever OS to be installed, not only Linux, so they have to follow standards (UEFI), instead of focusing on a Linux thing, such as device tree.
On embedded systems, OS and everything else are programmed once by the vendor and never again by the user. The OS is part of the firmware. So no need to worry about the OS support matrix, and just have a 1-to-1 relationship between the board and your OS image. U-Boot, kernel, initramfs, device tree blob reside on the same flash storage (i.e. NAND). So developers have access and control to what to be deployed as the device tree (must match real hardware though).
Hardware designers should be able to provide both an ACPI table and a device tree. Depending on the receiver, one will be preferred.
References:
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IMHO
ACPI and DT are used for similar purposes, but they have their unique functionalities. Nowadays the effort of defining ACPI configs in DT.
ACPI and DT are used to solve different issues:
Device tree is mostly passed to the linux kernel before it boots up. ACPI is usually loaded while linux kernel is booting (check Documentation/acpi/enumeration.txt for more info)
for any other thing just comment.
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ACPI and DT used in different architecture.
you can manually differentiate this inside linux kernel source code.
Reference:
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