Unverified Commit ea3de9ce authored by Evan Green's avatar Evan Green Committed by Palmer Dabbelt
Browse files

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: default avatarPalmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: default avatarEvan Green <evan@rivosinc.com>
Reviewed-by: default avatarConor Dooley <conor.dooley@microchip.com>
Reviewed-by: default avatarHeiko Stuebner <heiko.stuebner@vrull.eu>
Tested-by: default avatarHeiko Stuebner <heiko.stuebner@vrull.eu>
Reviewed-by: default avatarPaul Walmsley <paul.walmsley@sifive.com>
Link: https://lore.kernel.org/r/20230407231103.2622178-3-evan@rivosinc.com


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent ff77cf5b

Documentation/riscv/hwprobe.rst

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.. 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.

Documentation/riscv/index.rst

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@@ -7,6 +7,7 @@ RISC-V architecture 


    boot-image-header

    vm-layout

    hwprobe

    patch-acceptance

    uabi

arch/riscv/include/asm/hwprobe.h

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/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */

/*

 * Copyright 2023 Rivos, Inc

 */



#ifndef _ASM_HWPROBE_H

#define _ASM_HWPROBE_H



#include <uapi/asm/hwprobe.h>



#define RISCV_HWPROBE_MAX_KEY 2



#endif

arch/riscv/include/asm/syscall.h

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@@ -10,6 +10,7 @@ 
#ifndef _ASM_RISCV_SYSCALL_H

#define _ASM_RISCV_SYSCALL_H



#include <asm/hwprobe.h>

#include <uapi/linux/audit.h>

#include <linux/sched.h>

#include <linux/err.h>
@@ -75,4 +76,7 @@ static inline int syscall_get_arch(struct task_struct *task) 
}



asmlinkage long sys_riscv_flush_icache(uintptr_t, uintptr_t, uintptr_t);



asmlinkage long sys_riscv_hwprobe(struct riscv_hwprobe *, size_t, size_t,

				  unsigned long *, unsigned int);

#endif	/* _ASM_RISCV_SYSCALL_H */

arch/riscv/include/uapi/asm/hwprobe.h

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/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */

/*

 * Copyright 2023 Rivos, Inc

 */



#ifndef _UAPI_ASM_HWPROBE_H

#define _UAPI_ASM_HWPROBE_H



#include <linux/types.h>



/*

 * Interface for probing hardware capabilities from userspace, see

 * Documentation/riscv/hwprobe.rst for more information.

 */

struct riscv_hwprobe {

	__s64 key;

	__u64 value;

};



#define RISCV_HWPROBE_KEY_MVENDORID	0

#define RISCV_HWPROBE_KEY_MARCHID	1

#define RISCV_HWPROBE_KEY_MIMPID	2

/* Increase RISCV_HWPROBE_MAX_KEY when adding items. */



#endif