36d842d654
The "count" parameter associated with the 'cpus' parameter of the hwprobe syscall is the size in bytes of 'cpus'. Naming it 'cpu_count' may mislead users (it did me) to think it's the number of CPUs that are or can be represented by 'cpus' instead. This is particularly easy (IMO) to get wrong since 'cpus' is documented to be defined by CPU_SET(3) and CPU_SET(3) also documents a CPU_COUNT() (the number of CPUs in set) macro. CPU_SET(3) refers to the size of cpu sets with 'setsize'. Adopt 'cpusetsize' for the hwprobe parameter and specifically state it is in bytes in Documentation/riscv/hwprobe.rst to clarify. Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com> Reviewed-by: Conor Dooley <conor.dooley@microchip.com> Signed-off-by: Andrew Jones <ajones@ventanamicro.com> Link: https://lore.kernel.org/r/20231122164700.127954-7-ajones@ventanamicro.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
106 lines
4.7 KiB
ReStructuredText
106 lines
4.7 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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RISC-V Hardware Probing Interface
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---------------------------------
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The RISC-V hardware probing interface is based around a single syscall, which
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is defined in <asm/hwprobe.h>::
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struct riscv_hwprobe {
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__s64 key;
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__u64 value;
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};
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long sys_riscv_hwprobe(struct riscv_hwprobe *pairs, size_t pair_count,
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size_t cpusetsize, cpu_set_t *cpus,
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unsigned int flags);
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The arguments are split into three groups: an array of key-value pairs, a CPU
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set, and some flags. The key-value pairs are supplied with a count. Userspace
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must prepopulate the key field for each element, and the kernel will fill in the
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value if the key is recognized. If a key is unknown to the kernel, its key field
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will be cleared to -1, and its value set to 0. The CPU set is defined by
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CPU_SET(3) with size ``cpusetsize`` bytes. For value-like keys (eg. vendor,
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arch, impl), the returned value will only be valid if all CPUs in the given set
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have the same value. Otherwise -1 will be returned. For boolean-like keys, the
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value returned will be a logical AND of the values for the specified CPUs.
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Usermode can supply NULL for ``cpus`` and 0 for ``cpusetsize`` as a shortcut for
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all online CPUs. There are currently no flags, this value must be zero for
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future compatibility.
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On success 0 is returned, on failure a negative error code is returned.
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The following keys are defined:
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* :c:macro:`RISCV_HWPROBE_KEY_MVENDORID`: Contains the value of ``mvendorid``,
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as defined by the RISC-V privileged architecture specification.
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* :c:macro:`RISCV_HWPROBE_KEY_MARCHID`: Contains the value of ``marchid``, as
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defined by the RISC-V privileged architecture specification.
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* :c:macro:`RISCV_HWPROBE_KEY_MIMPLID`: Contains the value of ``mimplid``, as
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defined by the RISC-V privileged architecture specification.
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* :c:macro:`RISCV_HWPROBE_KEY_BASE_BEHAVIOR`: A bitmask containing the base
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user-visible behavior that this kernel supports. The following base user ABIs
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are defined:
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* :c:macro:`RISCV_HWPROBE_BASE_BEHAVIOR_IMA`: Support for rv32ima or
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rv64ima, as defined by version 2.2 of the user ISA and version 1.10 of the
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privileged ISA, with the following known exceptions (more exceptions may be
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added, but only if it can be demonstrated that the user ABI is not broken):
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* The ``fence.i`` instruction cannot be directly executed by userspace
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programs (it may still be executed in userspace via a
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kernel-controlled mechanism such as the vDSO).
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* :c:macro:`RISCV_HWPROBE_KEY_IMA_EXT_0`: A bitmask containing the extensions
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that are compatible with the :c:macro:`RISCV_HWPROBE_BASE_BEHAVIOR_IMA`:
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base system behavior.
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* :c:macro:`RISCV_HWPROBE_IMA_FD`: The F and D extensions are supported, as
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defined by commit cd20cee ("FMIN/FMAX now implement
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minimumNumber/maximumNumber, not minNum/maxNum") of the RISC-V ISA manual.
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* :c:macro:`RISCV_HWPROBE_IMA_C`: The C extension is supported, as defined
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by version 2.2 of the RISC-V ISA manual.
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* :c:macro:`RISCV_HWPROBE_IMA_V`: The V extension is supported, as defined by
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version 1.0 of the RISC-V Vector extension manual.
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* :c:macro:`RISCV_HWPROBE_EXT_ZBA`: The Zba address generation extension is
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supported, as defined in version 1.0 of the Bit-Manipulation ISA
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extensions.
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* :c:macro:`RISCV_HWPROBE_EXT_ZBB`: The Zbb extension is supported, as defined
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in version 1.0 of the Bit-Manipulation ISA extensions.
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* :c:macro:`RISCV_HWPROBE_EXT_ZBS`: The Zbs extension is supported, as defined
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in version 1.0 of the Bit-Manipulation ISA extensions.
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* :c:macro:`RISCV_HWPROBE_EXT_ZICBOZ`: The Zicboz extension is supported, as
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ratified in commit 3dd606f ("Create cmobase-v1.0.pdf") of riscv-CMOs.
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* :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains performance
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information about the selected set of processors.
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* :c:macro:`RISCV_HWPROBE_MISALIGNED_UNKNOWN`: The performance of misaligned
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accesses is unknown.
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* :c:macro:`RISCV_HWPROBE_MISALIGNED_EMULATED`: Misaligned accesses are
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emulated via software, either in or below the kernel. These accesses are
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always extremely slow.
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* :c:macro:`RISCV_HWPROBE_MISALIGNED_SLOW`: Misaligned accesses are slower
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than equivalent byte accesses. Misaligned accesses may be supported
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directly in hardware, or trapped and emulated by software.
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* :c:macro:`RISCV_HWPROBE_MISALIGNED_FAST`: Misaligned accesses are faster
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than equivalent byte accesses.
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* :c:macro:`RISCV_HWPROBE_MISALIGNED_UNSUPPORTED`: Misaligned accesses are
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not supported at all and will generate a misaligned address fault.
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* :c:macro:`RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE`: An unsigned int which
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represents the size of the Zicboz block in bytes.
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