/*-
 * Copyright (c) 2018 Justin Hibbits
 * Copyright (c) 2013 The FreeBSD Foundation
 * Copyright (c) 2013 David E. O'Brien <obrien@NUXI.org>
 * Copyright (c) 2012 Konstantin Belousov <kib@FreeBSD.org>
 * All rights reserved.
 *
 * Portions of this software were developed by Konstantin Belousov
 * under sponsorship from the FreeBSD Foundation.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer
 *    in this position and unchanged.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/conf.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/random.h>
#include <sys/systm.h>

#include <machine/cpu.h>
#include <machine/md_var.h>

#include <dev/random/randomdev.h>

/*
 * Power ISA 3.0 adds a "darn" instruction (Deliver A Random Number).  The RNG
 * backing this instruction conforms to NIST SP800-90B and SP800-90C at the
 * point of hardware design, and provides a minimum of 0.5 bits of entropy per
 * bit.
 */

#define RETRY_COUNT     10

static u_int random_darn_read(void *, u_int);

static const struct random_source random_darn = {
        .rs_ident = "PowerISA DARN random number generator",
        .rs_source = RANDOM_PURE_DARN,
        .rs_read = random_darn_read
};

static inline int
darn_rng_store(u_long *buf)
{
        u_long rndval;
        int retry;

        for (retry = RETRY_COUNT; retry > 0; --retry) {
                /* "DARN %rN, 1" instruction */
                /*
                 * Arguments for DARN: rN and "L", where "L" can be one of:
                 * 0 - 32-bit conditional random number
                 * 1 - Conditional random number (conditioned to remove bias)
                 * 2 - Raw random number         (unprocessed, may include bias)
                 * 3 - Reserved
                 */
                __asm __volatile(".long 0x7c0105e6 | (%0 << 21)" :
                    "+r"(rndval));
                if (rndval != ~0)
                        break;
        }

        *buf = rndval;
        return (retry);
}

/* It is required that buf length is a multiple of sizeof(u_long). */
static u_int
random_darn_read(void *buf, u_int c)
{
        u_long *b, rndval;
        u_int count;

        KASSERT(c % sizeof(*b) == 0, ("partial read %d", c));
        b = buf;
        for (count = c; count > 0; count -= sizeof(*b)) {
                if (darn_rng_store(&rndval) == 0)
                        break;
                *b++ = rndval;
        }
        return (c - count);
}

static int
darn_modevent(module_t mod, int type, void *unused)
{
        int error = 0;

        switch (type) {
        case MOD_LOAD:
                if (cpu_features2 & PPC_FEATURE2_DARN) {
                        random_source_register(&random_darn);
                        printf("random: fast provider: \"%s\"\n", random_darn.rs_ident);
                }
                break;

        case MOD_UNLOAD:
                if (cpu_features2 & PPC_FEATURE2_DARN)
                        random_source_deregister(&random_darn);
                break;

        case MOD_SHUTDOWN:
                break;

        default:
                error = EOPNOTSUPP;
                break;

        }

        return (error);
}

static moduledata_t darn_mod = {
        "darn",
        darn_modevent,
        0
};

DECLARE_MODULE(darn, darn_mod, SI_SUB_RANDOM, SI_ORDER_FOURTH);
MODULE_VERSION(darn, 1);
MODULE_DEPEND(darn, random_harvestq, 1, 1, 1);