/* 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 */