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995f226f3f
When -march=rv64im_zalrsc_zicsr is used, provide atomic operations and locks using lr and sc instructions only. Signed-off-by: Chao-ying Fu <cfu@mips.com> Reviewed-by: Anup Patel <anup@brainfault.org> Link: https://lore.kernel.org/r/20250226014727.19710-1-cfu@mips.com Signed-off-by: Anup Patel <anup@brainfault.org>
49 lines
1.8 KiB
Markdown
49 lines
1.8 KiB
Markdown
OpenSBI Platform Requirements
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=============================
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The RISC-V platform requirements for OpenSBI can change over time
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with advances in RISC-V specifications and ecosystem.
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To handle this, we have two types of RISC-V platform requirements:
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1. **Base platform requirements** which apply to all OpenSBI releases
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2. **Release specific platform requirements** which apply to a OpenSBI
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release and later releases
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Currently, we don't have any **Release specific platform requirements**,
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but such platform requirements will be added in future.
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Base Platform Requirements
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--------------------------
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The base RISC-V platform requirements for OpenSBI are as follows:
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1. At least rv32ima_zicsr or rv64ima_zicsr required on all HARTs
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* Users may restrict the usage of atomic instructions to lr/sc
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via rv32im_zalrsc_zicsr or rv64im_zalrsc_zicsr if preferred
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2. At least one HART should have S-mode support because:
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* SBI calls are meant for RISC-V S-mode (Supervisor mode)
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* OpenSBI implements SBI calls for S-mode software
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3. The MTVEC CSR on all HARTs must support direct mode
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4. The PMP CSRs are optional. If PMP CSRs are not implemented then
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OpenSBI cannot protect M-mode firmware and secured memory regions
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5. The TIME CSR is optional. If TIME CSR is not implemented in
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hardware then a 64-bit MMIO counter is required to track time
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and emulate TIME CSR
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6. Hardware support for injecting M-mode software interrupts on
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a multi-HART platform
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The RISC-V extensions not covered by rv32ima_zicsr or rv64ima_zicsr are optional
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for OpenSBI. Although, OpenSBI will detect and handle some of these
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optional RISC-V extensions at runtime.
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The optional RISC-V extensions handled by OpenSBI at runtime are:
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* D-extension: Double precision floating point
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* F-extension: Single precision floating point
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* H-extension: Hypervisor
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