Hi Atish, Thanks for this. Comments below.
On 16/10/2020 02:10, Atish Patra wrote:
This patch adds all minimum mandatory requirements to make RISC-V compatible with EBBR. Signed-off-by: Atish Patra <atish.pa...@wdc.com> --- source/chapter1-about.rst | 42 +++++++++++++++++++++++++++++++-- source/chapter2-uefi.rst | 10 +++++++- source/chapter3-secureworld.rst | 14 +++++++++++ source/references.rst | 4 ++++ 4 files changed, 67 insertions(+), 3 deletions(-) diff --git a/source/chapter1-about.rst b/source/chapter1-about.rst index 3db3f3280448..6927c87a125f 100644 --- a/source/chapter1-about.rst +++ b/source/chapter1-about.rst @@ -152,9 +152,10 @@ operating system. SBBR is targeted at the server ecosystem and places strict requirements on the platform to ensure cross vendor interoperability. EBBR on the other hand allows more flexibility to support embedded designs -which do not fit within the SBBR model. -For example, a platform that isn't SBBR compliant because the SoC is only +which do not fit within the SBBR model. For example, a platform that isn't SBBR compliant because the SoC is only
This hunk is a no-op change to the content and should be dropped from the patch, but it's a good opportunity to bring up a writing(coding) style comment. :-D As much as possible the EBBR source files should use "semantic linefeeds" with one sentence per line because when changes are made it eliminate diff hunks due to paragraph reflow. Here's how Brian Kernighan described it: Hints for Preparing Documents Most documents go through several versions (always more than you expected) before they are finally finished. Accordingly, you should do whatever possible to make the job of changing them easy. First, when you do the purely mechanical operations of typing, type so subsequent editing will be easy. Start each sentence on a new line. Make lines short, and break lines at natural places, such as after commas and semicolons, rather than randomly. Since most people change documents by rewriting phrases and adding, deleting and rearranging sentences, these precautions simplify any editing you have to do later. Brian W. Kernighan, 1974 Source : http://rhodesmill.org/brandon/2012/one-sentence-per-line/ I'll propose a patch adding this guidance to the EBBR repo.
supported using Devicetree could be EBBR compliant, but not SBBR compliant. +EBBR also supports multiple architectures such as AArch64 & RISC-V. However, RISC-V +is not compatible with SBBR. Thus, a EBBR compliant RISC-V platform would not be SBBR compliant.
This section is primarily commentary about the purpose of EBBR and how it compares with other specifications. Rather than defining where EBBR isn't aligned with SBBR, I'd rather rework the paragraph to state that EBBR is aligned with SBBR on AArch64 platforms. How about this for new text? --- This specification was inspired by the Server Base Boot Requirements specification [SBBR]_ used by the Arm AArch64 architecture. SBBR is targeted at the server ecosystem, and places strict requirements on the firmware interfaces presented to OSes to ensure cross vendor interoperability. Similarly, EBBR provides requirements on firmware interfaces using many of the same technologies, but provides more flexibility to support embedded designs which do not align with server platform requirements. EBBR strives to remain aligned with SBBR by requiring the same interfaces where possible, and ensuring EBBR requirements are not mutually exclusive to SBBR. For example, SBBR requires an ACPI system description, but EBBR allows either ACPI or a Devicetree. If ACPI support was added to an EBBR platform, it would still retain EBBR compliance. By definition, this means that all Arm SBBR compliant systems are also EBBR compliant, but the converse is not true. --- I won't be committing this as-is because I still need to do a bit more rework to transition from SBBR to BBR as part of Arm SystemReady. There is a bunch of AArch64 text that will get pulled out of EBBR because things like exception level handling are detailed properly in the BBR now. Details here: https://developer.arm.com/architectures/system-architectures/arm-systemready https://developer.arm.com/documentation/den0044/latest
By definition, all SBBR compliant systems are also EBBR compliant, but the converse is not true. @@ -228,6 +229,43 @@ This document uses the following terms and abbreviations. Original Equipment Manufacturer. In this document, the final device manufacturer. + RISC-V + An open standard Instruction Set Architecture (ISA) based on Reduced Instruction + Set Architecture (RISC). + + HART + Hardware thread in RISC-V. This is the hardware execution context that contains + all the state mandated by the ISA. + + M Mode + Machine mode is the most secure and privileged mode in RISC-V.
Nit: "M Mode" here, but in the spec text "M-Mode" is used. Should be identical.
+ + S Mode + Supervisor mode is the next secure mode where virtual memory is enabled. + + HS Mode + Hypervisor-extended-supervisor mode which virtualizes the supervisor mode. + + U Mode + User mode where userspace application is expected to run. + + HSM + Hart State Management (HSM) is an SBI extension that enables the supervisor + mode software to implement ordered booting. + + SEE + Supervisor Execution Environment in RISC-V. This can be M mode or HS mode. + + SBI + Supervisor Binary Interface. This is an interface between SEE and supervisor + mode in RISC-V. + + RV32 + 32 bit execution mode in RISC-V. + + RV64 + 64 bit execution mode in RISC-V. > +
I disagree with Daniel. I think all the RISC-V specific terms should be collected into a sub header, and the same should be done for ARM and AArch64. Mixing architecture specific terms together seems confusing to me.
SiP Silicon Partner. In this document, the silicon manufacturer. diff --git a/source/chapter2-uefi.rst b/source/chapter2-uefi.rst index 74ef70e29784..ad9d9543555e 100644 --- a/source/chapter2-uefi.rst +++ b/source/chapter2-uefi.rst @@ -36,7 +36,7 @@ Resident UEFI firmware might target a specific privilege level. In contrast, UEFI Loaded Images, such as third-party drivers and boot applications, must not contain any built-in assumptions that they are to be loaded at a given privilege level during boot time since they can, for example, -legitimately be loaded into either EL1 or EL2 on AArch64. +legitimately be loaded into either EL1 or EL2 on AArch64 and HS or S mode in RISC-V. AArch64 Exception Levels ------------------------ @@ -59,6 +59,14 @@ UEFI-compliant Operating System. In this instance, the UEFI boot-time environment can be provided, as a virtualized service, by the hypervisor and not as part of the host firmware. +RISC-V privilege levels +----------------------- + +UEFI shall execute in RV32/RV64 mode either in S or HS mode depending on whether +or not virtualization is supported in hardware and available at OS load time. +If the UEFI firmware is running in HS mode, the hypervisor is responsible for +providing the virtualized boot-time/runtime services. + UEFI Boot Services ================== diff --git a/source/chapter3-secureworld.rst b/source/chapter3-secureworld.rst index 9c51bca24f33..ad5c8fc17e40 100644 --- a/source/chapter3-secureworld.rst +++ b/source/chapter3-secureworld.rst @@ -27,3 +27,17 @@ Platforms without EL3 must implement one of: However, the spin table protocol is strongly discouraged. Future versions of this specification will only allow PSCI, and PSCI should be implemented in all new designs. + + +RISC-V Multiprocessor Startup protocol +====================================== +The firmware resident in M-mode or hypervisor running in HS mode must implement +and conform to at least Supervisor Binary Specification [SBI]_ v0.2 with HART +State Management(HSM) extension for both RV32 and RV64. In addition to that, the +firmware must ensure the following condition before jumping to the UEFI +application. + +- The device tree must contain a property named **boot-hartid** under the */chosen* + node. This property must indicate the id of the booting hart. There is no support + for ACPI in RISC-V yet. That's why, passing of the boot hart id via ACPI tables + has not been defined yet. diff --git a/source/references.rst b/source/references.rst index 1eb05090647e..9c96cb977c7e 100644 --- a/source/references.rst +++ b/source/references.rst @@ -23,3 +23,7 @@ .. [UEFI] `Unified Extensable Firmware Interface Specification v2.8 Errata A <https://uefi.org/sites/default/files/resources/UEFI_Spec_2_8_A_Feb14.pdf>`_, February 2020, `UEFI Forum <http://www.uefi.org>`_ + +.. [SBI] `Supervisor Binary Interface (SBI)
Should be `RISC-V Supervisor Binary Interface (SBI)`
+ <https://github.com/riscv/riscv-sbi-doc/blob/master/riscv-sbi.adoc>`_ + 11 October 2020, `RISC-V International <https://riscv.org/>`_
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