// SPDX-License-Identifier: GPL-2.0
/*
 * CZ.NIC's Turris Omnia MCU TRNG driver
 *
 * 2024 by Marek Behún <kabel@kernel.org>
 */

#include <linux/completion.h>
#include <linux/container_of.h>
#include <linux/errno.h>
#include <linux/hw_random.h>
#include <linux/i2c.h>
#include <linux/interrupt.h>
#include <linux/minmax.h>
#include <linux/string.h>
#include <linux/types.h>

#include <linux/turris-omnia-mcu-interface.h>
#include "turris-omnia-mcu.h"

#define OMNIA_CMD_TRNG_MAX_ENTROPY_LEN  64

static irqreturn_t omnia_trng_irq_handler(int irq, void *dev_id)
{
        struct omnia_mcu *mcu = dev_id;

        complete(&mcu->trng_entropy_ready);

        return IRQ_HANDLED;
}

static int omnia_trng_read(struct hwrng *rng, void *data, size_t max, bool wait)
{
        struct omnia_mcu *mcu = container_of(rng, struct omnia_mcu, trng);
        u8 reply[1 + OMNIA_CMD_TRNG_MAX_ENTROPY_LEN];
        int err, bytes;

        if (!wait && !completion_done(&mcu->trng_entropy_ready))
                return 0;

        do {
                if (wait_for_completion_interruptible(&mcu->trng_entropy_ready))
                        return -ERESTARTSYS;

                err = omnia_cmd_read(mcu->client,
                                     OMNIA_CMD_TRNG_COLLECT_ENTROPY,
                                     reply, sizeof(reply));
                if (err)
                        return err;

                bytes = min3(reply[0], max, OMNIA_CMD_TRNG_MAX_ENTROPY_LEN);
        } while (wait && !bytes);

        memcpy(data, &reply[1], bytes);

        return bytes;
}

int omnia_mcu_register_trng(struct omnia_mcu *mcu)
{
        struct device *dev = &mcu->client->dev;
        u8 dummy;
        int err;

        if (!(mcu->features & OMNIA_FEAT_TRNG))
                return 0;

        /*
         * If someone else cleared the TRNG interrupt but did not read the
         * entropy, a new interrupt won't be generated, and entropy collection
         * will be stuck. Ensure an interrupt will be generated by executing
         * the collect entropy command (and discarding the result).
         */
        err = omnia_cmd_read(mcu->client, OMNIA_CMD_TRNG_COLLECT_ENTROPY,
                             &dummy, 1);
        if (err)
                return err;

        init_completion(&mcu->trng_entropy_ready);

        err = omnia_mcu_request_irq(mcu, OMNIA_INT_TRNG, omnia_trng_irq_handler,
                                    "turris-omnia-mcu-trng");
        if (err)
                return dev_err_probe(dev, err, "Cannot request TRNG IRQ\n");

        mcu->trng.name = "turris-omnia-mcu-trng";
        mcu->trng.read = omnia_trng_read;

        err = devm_hwrng_register(dev, &mcu->trng);
        if (err)
                return dev_err_probe(dev, err, "Cannot register TRNG\n");

        return 0;
}