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docs: Add platform requirements document

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We add platform requirements document to clarify OpenSBI
expectations from a RISC-V platform.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Bin Meng <bin.meng@windriver.com>
This commit is contained in:
Anup Patel
2020-05-05 09:46:46 +05:30
committed by Anup Patel
parent b4efa70d12
commit dfd9dd67dc
3 changed files with 47 additions and 0 deletions
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README.md
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@@ -218,6 +218,7 @@ Detailed documentation of various aspects of OpenSBI can be found under the
* [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
@@ -270,6 +271,7 @@ make I=<install_directory> install_docs
[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

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docs/doxygen.cfg
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INPUT = @@SRC_DIR@@/README.md \
@@SRC_DIR@@/docs/contributing.md \
@@SRC_DIR@@/docs/platform_guide.md \
@@SRC_DIR@@/docs/platform_requirements.md \
@@SRC_DIR@@/docs/library_usage.md \
@@SRC_DIR@@/docs/firmware \
@@SRC_DIR@@/docs/platform \

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docs/platform_requirements.md Normal file
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OpenSBI Platform Requirements
=============================
The RISC-V platform requirements for OpenSBI can change over time
with advances in RISC-V specifications and ecosystem.
To handle this, we have two types of RISC-V platform requirements:
1. **Base platform requirements** which apply to all OpenSBI releases
2. **Release specific platform requirements** which apply to a OpenSBI
release and later releases
Currently, we don't have any **Release specific platform requirements**
but such platform requirements will be added in future.
Base Platform Requirements
--------------------------
The base RISC-V platform requirements for OpenSBI are as follows:
1. At least rv32ima or rv64ima required on all HARTs
2. At least one HART should have S-mode support because:
* SBI calls are meant for RISC-V S-mode (Supervisor mode)
* OpenSBI implements SBI calls for S-mode software
3. The MTVEC CSR on all HARTs must support direct mode
4. The PMP CSRs are optional. If PMP CSRs are not implemented then
OpenSBI cannot protect M-mode firmware and secured memory regions
5. The TIME CSR is optional. If TIME CSR is not implemented in
hardware then a 64-bit MMIO counter is required to track time
and emulate TIME CSR
6. Hardware support for injecting M-mode software interrupts on
a multi-HART platform
The RISC-V extensions not covered by rv32ima or rv64ima are optional
for OpenSBI. Although, OpenSBI will detect and handle some of these
optional RISC-V extensions at runtime.
The optional RISC-V extensions handled by OpenSBI at runtime are:
* D-extension: Double precision floating point
* F-extension: Single precision floating point
* H-extension: Hypervisor