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+RISC-V Open Source Supervisor Binary Interface (OpenSBI)
+========================================================
+
+Copyright and License
+---------------------
+
+The OpenSBI project is copyright (c) 2019 Western Digital Corporation
+or its affiliates and other contributors.
+
+It is distributed under the terms of the BSD 2-clause license
+("Simplified BSD License" or "FreeBSD License", SPDX: *BSD-2-Clause*).
+A copy of this license with OpenSBI copyright can be found in the file
+[COPYING.BSD].
+
+All source files in OpenSBI contain the 2-Clause BSD license SPDX short
+identifier in place of the full license text.
+
+```
+SPDX-License-Identifier:    BSD-2-Clause
+```
+
+This enables machine processing of license information based on the SPDX
+License Identifiers that are available on the [SPDX] web site.
+
+OpenSBI source code also contains code reused from other projects as listed
+below. The original license text of these projects is included in the source
+files where the reused code is present.
+
+* The libfdt source code is disjunctively dual licensed
+  (GPL-2.0+ OR BSD-2-Clause). Some of this project code is used in OpenSBI
+  under the terms of the BSD 2-Clause license. Any contributions to this
+  code must be made under the terms of both licenses.
+
+See also the [third party notices] file for more information.
+
+Introduction
+------------
+
+The **RISC-V Supervisor Binary Interface (SBI)** is the recommended interface
+between:
+
+1. A platform-specific firmware running in M-mode and a bootloader, a
+   hypervisor or a general-purpose OS executing in S-mode or HS-mode.
+2. A hypervisor running in HS-mode and a bootloader or a general-purpose OS
+   executing in VS-mode.
+
+The *RISC-V SBI specification* is maintained as an independent project by the
+RISC-V Foundation on [Github].
+
+The goal of the OpenSBI project is to provide an open-source reference
+implementation of the RISC-V SBI specifications for platform-specific firmwares
+executing in M-mode (case 1 mentioned above). An OpenSBI implementation can be
+easily extended by RISC-V platform and system-on-chip vendors to fit a
+particular hardware configuration.
+
+The main component of OpenSBI is provided in the form of a platform-independent
+static library **libsbi.a** implementing the SBI interface. A firmware or
+bootloader implementation can link against this library to ensure conformance
+with the SBI interface specifications. *libsbi.a* also defines an interface for
+integrating with platform-specific operations provided by the platform firmware
+implementation (e.g. console access functions, inter-processor interrupt
+control, etc).
+
+To illustrate the use of the *libsbi.a* library, OpenSBI also provides a set of
+platform-specific support examples. For each example, a platform-specific
+static library *libplatsbi.a* can be compiled. This library implements
+SBI call processing by integrating *libsbi.a* with the necessary
+platform-dependent hardware manipulation functions. For all supported platforms,
+OpenSBI also provides several runtime firmware examples built using the platform
+*libplatsbi.a*. These example firmwares can be used to replace the legacy
+*riscv-pk* bootloader (aka BBL) and enable the use of well-known bootloaders
+such as [U-Boot].
+
+Supported SBI version
+---------------------
+Currently, OpenSBI fully supports SBI specification *v0.2*. OpenSBI also
+supports Hart State Management (HSM) SBI extension starting from OpenSBI v0.7.
+HSM extension allows S-mode software to boot all the harts a defined order
+rather than legacy method of random booting of harts. As a result, many
+required features such as CPU hotplug, kexec/kdump can also be supported easily
+in S-mode. HSM extension in OpenSBI is implemented in a non-backward compatible
+manner to reduce the maintenance burden and avoid confusion. That's why, any
+S-mode software using OpenSBI will not be able to boot more than 1 hart if HSM
+extension is not supported in S-mode.
+
+Linux kernel already supports SBI v0.2 and HSM SBI extension starting from
+**v5.7-rc1**. If you are using an Linux kernel older than **5.7-rc1** or any
+other S-mode software without HSM SBI extension, you should stick to OpenSBI
+v0.6 to boot all the harts. For a UMP systems, it doesn't matter.
+
+N.B. Any S-mode boot loader (i.e. U-Boot) doesn't need to support HSM extension,
+as it doesn't need to boot all the harts. The operating system should be
+capable enough to bring up all other non-booting harts using HSM extension.
+
+Required Toolchain
+------------------
+
+OpenSBI can be compiled natively or cross-compiled on a x86 host. For
+cross-compilation, you can build your own toolchain or just download
+a prebuilt one from the [Bootlin toolchain repository].
+
+Please note that only a 64-bit version of the toolchain is available in
+the Bootlin toolchain repository for now.
+
+Building and Installing the OpenSBI Platform-Independent Library
+----------------------------------------------------------------
+
+The OpenSBI platform-independent static library *libsbi.a* can be compiled
+natively or it can be cross-compiled on a host with a different base
+architecture than RISC-V.
+
+For cross-compiling, the environment variable *CROSS_COMPILE* must be defined
+to specify the name prefix of the RISC-V compiler toolchain executables, e.g.
+*riscv64-unknown-elf-* if the gcc executable used is *riscv64-unknown-elf-gcc*.
+
+To build *libsbi.a* simply execute:
+```
+make
+```
+
+All compiled binaries as well as the resulting *libsbi.a* static library file
+will be placed in the *build/lib* directory. To specify an alternate build root
+directory path, run:
+```
+make O=<build_directory>
+```
+
+To generate files to be installed for using *libsbi.a* in other projects, run:
+```
+make install
+```
+
+This will create the *install* directory with all necessary include files
+copied under the *install/include* directory and the library file copied into
+the *install/lib* directory. To specify an alternate installation root
+directory path, run:
+```
+make I=<install_directory> install
+```
+
+Building and Installing a Reference Platform Static Library and Firmware
+------------------------------------------------------------------------
+
+When the *PLATFORM=<platform_subdir>* argument is specified on the make command
+line, the platform-specific static library *libplatsbi.a* and firmware examples
+are built for the platform *<platform_subdir>* present in the directory
+*platform* in the OpenSBI top directory. For example, to compile the platform
+library and the firmware examples for the QEMU RISC-V *virt* machine,
+*<platform_subdir>* should be *generic*.
+
+To build *libsbi.a*, *libplatsbi.a* and the firmware for one of the supported
+platforms, run:
+```
+make PLATFORM=<platform_subdir>
+```
+
+An alternate build directory path can also be specified:
+```
+make PLATFORM=<platform_subdir> O=<build_directory>
+```
+
+The platform-specific library *libplatsbi.a* will be generated in the
+*build/platform/<platform_subdir>/lib* directory. The platform firmware files
+will be under the *build/platform/<platform_subdir>/firmware* directory.
+The compiled firmwares will be available in two different formats: an ELF file
+and an expanded image file.
+
+To install *libsbi.a*, *libplatsbi.a*, and the compiled firmwares, run:
+```
+make PLATFORM=<platform_subdir> install
+```
+
+This will copy the compiled platform-specific libraries and firmware files
+under the *install/platform/<platform_subdir>/* directory. An alternate
+install root directory path can be specified as follows:
+```
+make PLATFORM=<platform_subdir> I=<install_directory> install
+```
+
+In addition, platform-specific configuration options can be specified with the
+top-level make command line. These options, such as *PLATFORM_<xyz>* or
+*FW_<abc>*, are platform-specific and described in more details in the
+*docs/platform/<platform_name>.md* files and
+*docs/firmware/<firmware_name>.md* files.
+
+Building 32-bit / 64-bit OpenSBI Images
+---------------------------------------
+By default, building OpenSBI generates 32-bit or 64-bit images based on the
+supplied RISC-V cross-compile toolchain. For example if *CROSS_COMPILE* is set
+to *riscv64-unknown-elf-*, 64-bit OpenSBI images will be generated. If building
+32-bit OpenSBI images, *CROSS_COMPILE* should be set to a toolchain that is
+pre-configured to generate 32-bit RISC-V codes, like *riscv32-unknown-elf-*.
+
+However it's possible to explicitly specify the image bits we want to build with
+a given RISC-V toolchain. This can be done by setting the environment variable
+*PLATFORM_RISCV_XLEN* to the desired width, for example:
+
+```
+export CROSS_COMPILE=riscv64-unknown-elf-
+export PLATFORM_RISCV_XLEN=32
+```
+
+will generate 32-bit OpenSBI images. And vice vesa.
+
+Contributing to OpenSBI
+-----------------------
+
+The OpenSBI project encourages and welcomes contributions. Contributions should
+follow the rules described in the OpenSBI [Contribution Guideline] document.
+In particular, all patches sent should contain a Signed-off-by tag.
+
+The [Contributors List] document provides a list of individuals and
+organizations actively contributing to the OpenSBI project.
+
+Documentation
+-------------
+
+Detailed documentation of various aspects of OpenSBI can be found under the
+*docs* directory. The documentation covers the following topics.
+
+* [Contribution Guideline]: Guideline for contributing code to OpenSBI project
+* [Library Usage]: API documentation of OpenSBI static library *libsbi.a*
+* [Platform Requirements]: Requirements for using OpenSBI on a platform
+* [Platform Support Guide]: Guideline for implementing support for new platforms
+* [Platform Documentation]: Documentation of the platforms currently supported.
+* [Firmware Documentation]: Documentation for the different types of firmware
+  examples build supported by OpenSBI.
+* [Domain Support]: Documentation for the OpenSBI domain support which helps
+  users achieve system-level partitioning using OpenSBI.
+
+OpenSBI source code is also well documented. For source level documentation,
+doxygen style is used. Please refer to the [Doxygen manual] for details on this
+format.
+
+Doxygen can be installed on Linux distributions using *.deb* packages using
+the following command.
+```
+sudo apt-get install doxygen doxygen-latex doxygen-doc doxygen-gui graphviz
+```
+
+For *.rpm* based Linux distributions, the following commands can be used.
+```
+sudo yum install doxygen doxygen-latex doxywizard graphviz
+```
+or
+```
+sudo yum install doxygen doxygen-latex doxywizard graphviz
+```
+
+To build a consolidated *refman.pdf* of all documentation, run:
+```
+make docs
+```
+or
+```
+make O=<build_directory> docs
+```
+
+the resulting *refman.pdf* will be available under the directory
+*<build_directory>/docs/latex*. To install this file, run:
+```
+make install_docs
+```
+or
+```
+make I=<install_directory> install_docs
+```
+
+*refman.pdf* will be installed under *<install_directory>/docs*.
+
+[Github]: https://github.com/riscv/riscv-sbi-doc
+[U-Boot]: https://www.denx.de/wiki/U-Boot/SourceCode
+[Bootlin toolchain repository]: https://toolchains.bootlin.com/
+[COPYING.BSD]: COPYING.BSD
+[SPDX]: http://spdx.org/licenses/
+[Contribution Guideline]: docs/contributing.md
+[Contributors List]: CONTRIBUTORS.md
+[Library Usage]: docs/library_usage.md
+[Platform Requirements]: docs/platform_requirements.md
+[Platform Support Guide]: docs/platform_guide.md
+[Platform Documentation]: docs/platform/platform.md
+[Firmware Documentation]: docs/firmware/fw.md
+[Domain Support]: docs/domain_support.md
+[Doxygen manual]: http://www.doxygen.nl/manual/index.html
+[Kendryte standalone SDK]: https://github.com/kendryte/kendryte-standalone-sdk
+[third party notices]: ThirdPartyNotices.md