// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2010 Michael Neuling IBM Corporation
 *
 * Driver for the pseries hardware RNG for POWER7+ and above
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/hw_random.h>
#include <asm/vio.h>


static int pseries_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
{
        u64 buffer[PLPAR_HCALL_BUFSIZE];
        int rc;

        rc = plpar_hcall(H_RANDOM, (unsigned long *)buffer);
        if (rc != H_SUCCESS) {
                pr_err_ratelimited("H_RANDOM call failed %d\n", rc);
                return -EIO;
        }
        memcpy(data, buffer, 8);

        /* The hypervisor interface returns 64 bits */
        return 8;
}

/*
 * pseries_rng_get_desired_dma - Return desired DMA allocate for CMO operations
 *
 * This is a required function for a driver to operate in a CMO environment
 * but this device does not make use of DMA allocations, return 0.
 *
 * Return value:
 *      Number of bytes of IO data the driver will need to perform well -> 0
 */
static unsigned long pseries_rng_get_desired_dma(struct vio_dev *vdev)
{
        return 0;
};

static struct hwrng pseries_rng = {
        .name           = KBUILD_MODNAME,
        .read           = pseries_rng_read,
};

static int pseries_rng_probe(struct vio_dev *dev,
                const struct vio_device_id *id)
{
        return hwrng_register(&pseries_rng);
}

static void pseries_rng_remove(struct vio_dev *dev)
{
        hwrng_unregister(&pseries_rng);
}

static const struct vio_device_id pseries_rng_driver_ids[] = {
        { "ibm,random-v1", "ibm,random"},
        { "", "" }
};
MODULE_DEVICE_TABLE(vio, pseries_rng_driver_ids);

static struct vio_driver pseries_rng_driver = {
        .name = KBUILD_MODNAME,
        .probe = pseries_rng_probe,
        .remove = pseries_rng_remove,
        .get_desired_dma = pseries_rng_get_desired_dma,
        .id_table = pseries_rng_driver_ids
};

static int __init rng_init(void)
{
        pr_info("Registering IBM pSeries RNG driver\n");
        return vio_register_driver(&pseries_rng_driver);
}

module_init(rng_init);

static void __exit rng_exit(void)
{
        vio_unregister_driver(&pseries_rng_driver);
}
module_exit(rng_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Michael Neuling <mikey@neuling.org>");
MODULE_DESCRIPTION("H/W RNG driver for IBM pSeries processors");