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/* SPDX-License-Identifier: GPL-2.0 */
/*
* Kernel interface for the RISCV arch_random_* functions
*
* Copyright (c) 2023 Rivos Inc.
*
*/
#ifndef ASM_RISCV_ARCHRANDOM_H
#define ASM_RISCV_ARCHRANDOM_H
#include <asm/csr.h>
#include <asm/processor.h>
#define SEED_RETRY_LOOPS 100
static inline bool __must_check csr_seed_long(unsigned long *v)
{
unsigned int retry = SEED_RETRY_LOOPS, valid_seeds = 0;
const int needed_seeds = sizeof(long) / sizeof(u16);
u16 *entropy = (u16 *)v;
do {
/*
* The SEED CSR must be accessed with a read-write instruction.
*/
unsigned long csr_seed = csr_swap(CSR_SEED, 0);
unsigned long opst = csr_seed & SEED_OPST_MASK;
switch (opst) {
case SEED_OPST_ES16:
entropy[valid_seeds++] = csr_seed & SEED_ENTROPY_MASK;
if (valid_seeds == needed_seeds)
return true;
break;
case SEED_OPST_DEAD:
pr_err_once("archrandom: Unrecoverable error\n");
return false;
case SEED_OPST_BIST:
case SEED_OPST_WAIT:
default:
cpu_relax();
continue;
}
} while (--retry);
return false;
}
static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)
{
return 0;
}
static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs)
{
if (!max_longs)
return 0;
/*
* If Zkr is supported and csr_seed_long succeeds, we return one long
* worth of entropy.
*/
if (riscv_has_extension_likely(RISCV_ISA_EXT_ZKR) && csr_seed_long(v))
return 1;
return 0;
}
#endif /* ASM_RISCV_ARCHRANDOM_H */
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