// SPDX-License-Identifier: GPL-2.0
/* Copyright (C) 2020 Xiphera Ltd. */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/err.h>
#include <linux/io.h>
#include <linux/hw_random.h>
#include <linux/platform_device.h>
#include <linux/delay.h>

#define CONTROL_REG                     0x00000000
#define STATUS_REG                      0x00000004
#define RAND_REG                        0x00000000

#define HOST_TO_TRNG_RESET              0x00000001
#define HOST_TO_TRNG_RELEASE_RESET      0x00000002
#define HOST_TO_TRNG_ENABLE             0x80000000
#define HOST_TO_TRNG_ZEROIZE            0x80000004
#define HOST_TO_TRNG_ACK_ZEROIZE        0x80000008
#define HOST_TO_TRNG_READ               0x8000000F

/* trng statuses */
#define TRNG_ACK_RESET                  0x000000AC
#define TRNG_SUCCESSFUL_STARTUP         0x00000057
#define TRNG_FAILED_STARTUP             0x000000FA
#define TRNG_NEW_RAND_AVAILABLE         0x000000ED

struct xiphera_trng {
        void __iomem *mem;
        struct hwrng rng;
};

static int xiphera_trng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
{
        struct xiphera_trng *trng = container_of(rng, struct xiphera_trng, rng);
        int ret = 0;

        while (max >= sizeof(u32)) {
                /* check for data */
                if (readl(trng->mem + STATUS_REG) == TRNG_NEW_RAND_AVAILABLE) {
                        *(u32 *)buf = readl(trng->mem + RAND_REG);
                        /*
                         * Inform the trng of the read
                         * and re-enable it to produce a new random number
                         */
                        writel(HOST_TO_TRNG_READ, trng->mem + CONTROL_REG);
                        writel(HOST_TO_TRNG_ENABLE, trng->mem + CONTROL_REG);
                        ret += sizeof(u32);
                        buf += sizeof(u32);
                        max -= sizeof(u32);
                } else {
                        break;
                }
        }
        return ret;
}

static int xiphera_trng_probe(struct platform_device *pdev)
{
        int ret;
        struct xiphera_trng *trng;
        struct device *dev = &pdev->dev;

        trng = devm_kzalloc(dev, sizeof(*trng), GFP_KERNEL);
        if (!trng)
                return -ENOMEM;

        trng->mem = devm_platform_ioremap_resource(pdev, 0);
        if (IS_ERR(trng->mem))
                return PTR_ERR(trng->mem);

        /*
         * the trng needs to be reset first which might not happen in time,
         * hence we incorporate a small delay to ensure proper behaviour
         */
        writel(HOST_TO_TRNG_RESET, trng->mem + CONTROL_REG);
        usleep_range(100, 200);

        if (readl(trng->mem + STATUS_REG) != TRNG_ACK_RESET) {
                /*
                 * there is a small chance the trng is just not ready yet,
                 * so we try one more time. If the second time fails, we give up
                 */
                usleep_range(100, 200);
                if (readl(trng->mem + STATUS_REG) != TRNG_ACK_RESET) {
                        dev_err(dev, "failed to reset the trng ip\n");
                        return -ENODEV;
                }
        }

        /*
         * once again, to ensure proper behaviour we sleep
         * for a while after zeroizing the trng
         */
        writel(HOST_TO_TRNG_RELEASE_RESET, trng->mem + CONTROL_REG);
        writel(HOST_TO_TRNG_ENABLE, trng->mem + CONTROL_REG);
        writel(HOST_TO_TRNG_ZEROIZE, trng->mem + CONTROL_REG);
        msleep(20);

        if (readl(trng->mem + STATUS_REG) != TRNG_SUCCESSFUL_STARTUP) {
                /* diagnose the reason for the failure */
                if (readl(trng->mem + STATUS_REG) == TRNG_FAILED_STARTUP) {
                        dev_err(dev, "trng ip startup-tests failed\n");
                        return -ENODEV;
                }
                dev_err(dev, "startup-tests yielded no response\n");
                return -ENODEV;
        }

        writel(HOST_TO_TRNG_ACK_ZEROIZE, trng->mem + CONTROL_REG);

        trng->rng.name = pdev->name;
        trng->rng.read = xiphera_trng_read;
        trng->rng.quality = 900;

        ret = devm_hwrng_register(dev, &trng->rng);
        if (ret) {
                dev_err(dev, "failed to register rng device: %d\n", ret);
                return ret;
        }

        return 0;
}

static const struct of_device_id xiphera_trng_of_match[] = {
        { .compatible = "xiphera,xip8001b-trng", },
        {},
};
MODULE_DEVICE_TABLE(of, xiphera_trng_of_match);

static struct platform_driver xiphera_trng_driver = {
        .driver = {
                .name = "xiphera-trng",
                .of_match_table = xiphera_trng_of_match,
        },
        .probe = xiphera_trng_probe,
};

module_platform_driver(xiphera_trng_driver);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Atte Tommiska");
MODULE_DESCRIPTION("Xiphera FPGA-based true random number generator driver");