diff options
| author | Evan Green | 2023-04-07 16:10:59 -0700 |
|---|---|---|
| committer | Palmer Dabbelt | 2023-04-18 15:48:14 -0700 |
| commit | ea3de9ce8aa280c5175c835bd3e94a3a9b814b74 (patch) | |
| tree | 835575d48af67ab432d8e3497d9156538f8e6668 /Documentation/riscv | |
| parent | ff77cf5b2e033d0bb5e3b7f83ebf65c5adc20d12 (diff) | |
RISC-V: Add a syscall for HW probing
We don't have enough space for these all in ELF_HWCAP{,2} and there's no
system call that quite does this, so let's just provide an arch-specific
one to probe for hardware capabilities. This currently just provides
m{arch,imp,vendor}id, but with the key-value pairs we can pass more in
the future.
Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Evan Green <evan@rivosinc.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
Tested-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
Reviewed-by: Paul Walmsley <paul.walmsley@sifive.com>
Link: https://lore.kernel.org/r/20230407231103.2622178-3-evan@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Diffstat (limited to 'Documentation/riscv')
| -rw-r--r-- | Documentation/riscv/hwprobe.rst | 41 | ||||
| -rw-r--r-- | Documentation/riscv/index.rst | 1 |
2 files changed, 42 insertions, 0 deletions
diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst new file mode 100644 index 000000000000..211828f706e3 --- /dev/null +++ b/Documentation/riscv/hwprobe.rst @@ -0,0 +1,41 @@ +.. SPDX-License-Identifier: GPL-2.0 + +RISC-V Hardware Probing Interface +--------------------------------- + +The RISC-V hardware probing interface is based around a single syscall, which +is defined in <asm/hwprobe.h>:: + + struct riscv_hwprobe { + __s64 key; + __u64 value; + }; + + long sys_riscv_hwprobe(struct riscv_hwprobe *pairs, size_t pair_count, + size_t cpu_count, cpu_set_t *cpus, + unsigned int flags); + +The arguments are split into three groups: an array of key-value pairs, a CPU +set, and some flags. The key-value pairs are supplied with a count. Userspace +must prepopulate the key field for each element, and the kernel will fill in the +value if the key is recognized. If a key is unknown to the kernel, its key field +will be cleared to -1, and its value set to 0. The CPU set is defined by +CPU_SET(3). For value-like keys (eg. vendor/arch/impl), the returned value will +be only be valid if all CPUs in the given set have the same value. Otherwise -1 +will be returned. For boolean-like keys, the value returned will be a logical +AND of the values for the specified CPUs. Usermode can supply NULL for cpus and +0 for cpu_count as a shortcut for all online CPUs. There are currently no flags, +this value must be zero for future compatibility. + +On success 0 is returned, on failure a negative error code is returned. + +The following keys are defined: + +* :c:macro:`RISCV_HWPROBE_KEY_MVENDORID`: Contains the value of ``mvendorid``, + as defined by the RISC-V privileged architecture specification. + +* :c:macro:`RISCV_HWPROBE_KEY_MARCHID`: Contains the value of ``marchid``, as + defined by the RISC-V privileged architecture specification. + +* :c:macro:`RISCV_HWPROBE_KEY_MIMPLID`: Contains the value of ``mimplid``, as + defined by the RISC-V privileged architecture specification. diff --git a/Documentation/riscv/index.rst b/Documentation/riscv/index.rst index 2e5b18fbb145..175a91db0200 100644 --- a/Documentation/riscv/index.rst +++ b/Documentation/riscv/index.rst @@ -7,6 +7,7 @@ RISC-V architecture boot-image-header vm-layout + hwprobe patch-acceptance uabi |