/*      $NetBSD: bcm2835_rng.c,v 1.17 2022/03/19 11:55:03 riastradh Exp $ */

/*-
 * Copyright (c) 2013 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Jared D. McNeill
 *
 * 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.
 * 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 NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``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 FOUNDATION OR CONTRIBUTORS
 * 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/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: bcm2835_rng.c,v 1.17 2022/03/19 11:55:03 riastradh Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/device.h>
#include <sys/kernel.h>
#include <sys/bus.h>
#include <sys/rndsource.h>

#include <arm/broadcom/bcm2835reg.h>
#include <arm/broadcom/bcm2835_intr.h>

#include <dev/fdt/fdtvar.h>

#define RNG_CTRL                0x00
#define  RNG_CTRL_EN            __BIT(0)
#define RNG_STATUS              0x04
#define  RNG_STATUS_CNT         __BITS(31,24)
#define RNG_DATA                0x08

#define RNG_DATA_MAX            256

struct bcm2835rng_softc {
        device_t                sc_dev;

        bus_space_tag_t         sc_iot;
        bus_space_handle_t      sc_ioh;

        krndsource_t            sc_rndsource;
};

static int bcmrng_match(device_t, cfdata_t, void *);
static void bcmrng_attach(device_t, device_t, void *);
static void bcmrng_get(size_t, void *);

CFATTACH_DECL_NEW(bcmrng_fdt, sizeof(struct bcm2835rng_softc),
    bcmrng_match, bcmrng_attach, NULL, NULL);

static const struct device_compatible_entry compat_data[] = {
        { .compat = "brcm,bcm2835-rng" },
        DEVICE_COMPAT_EOL
};

/* ARGSUSED */
static int
bcmrng_match(device_t parent, cfdata_t match, void *aux)
{
        struct fdt_attach_args * const faa = aux;

        return of_compatible_match(faa->faa_phandle, compat_data);
}

static void
bcmrng_attach(device_t parent, device_t self, void *aux)
{
        struct bcm2835rng_softc *sc = device_private(self);
        struct fdt_attach_args * const faa = aux;
        const int phandle = faa->faa_phandle;
        uint32_t ctrl;
        bus_addr_t addr;
        bus_size_t size;
        int error;

        aprint_naive("\n");
        aprint_normal(": RNG\n");

        sc->sc_dev = self;
        sc->sc_iot = faa->faa_bst;

        error = fdtbus_get_reg(phandle, 0, &addr, &size);
        if (error) {
                aprint_error_dev(sc->sc_dev, "unable to map device\n");
                return;
        }

        if (bus_space_map(sc->sc_iot, addr, size, 0,
            &sc->sc_ioh)) {
                aprint_error_dev(sc->sc_dev, "unable to map device\n");
                return;
        }

        /* discard initial numbers, broadcom says they are "less random" */
        bus_space_write_4(sc->sc_iot, sc->sc_ioh, RNG_STATUS, 0x40000);

        /* enable rng */
        ctrl = bus_space_read_4(sc->sc_iot, sc->sc_ioh, RNG_CTRL);
        ctrl |= RNG_CTRL_EN;
        bus_space_write_4(sc->sc_iot, sc->sc_ioh, RNG_CTRL, ctrl);

        /* set up an rndsource */
        rndsource_setcb(&sc->sc_rndsource, &bcmrng_get, sc);
        rnd_attach_source(&sc->sc_rndsource, device_xname(self), RND_TYPE_RNG,
            RND_FLAG_COLLECT_VALUE|RND_FLAG_HASCB);
}

static void
bcmrng_get(size_t bytes_wanted, void *arg)
{
        struct bcm2835rng_softc *sc = arg;
        uint32_t status, cnt;
        uint32_t buf[RNG_DATA_MAX]; /* 1k on the stack */

        while (bytes_wanted) {
                status = bus_space_read_4(sc->sc_iot, sc->sc_ioh, RNG_STATUS);
                cnt = __SHIFTOUT(status, RNG_STATUS_CNT);
                KASSERT(cnt < RNG_DATA_MAX);
                if (cnt == 0)
                        continue;       /* XXX Busy-waiting seems wrong...  */
                bus_space_read_multi_4(sc->sc_iot, sc->sc_ioh, RNG_DATA, buf,
                    cnt);
                rnd_add_data_sync(&sc->sc_rndsource, buf, (cnt * 4),
                    (cnt * 4 * NBBY));
                bytes_wanted -= MIN(bytes_wanted, (cnt * 4));
        }
        explicit_memset(buf, 0, sizeof(buf));
}