/* n2-drv.c: Niagara-2 RNG driver.
 *
 * Copyright (C) 2008, 2011 David S. Miller <davem@davemloft.net>
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/delay.h>
#include <linux/slab.h>
#include <linux/workqueue.h>
#include <linux/preempt.h>
#include <linux/hw_random.h>

#include <linux/of.h>
#include <linux/of_device.h>

#include <asm/hypervisor.h>

#include "n2rng.h"

#define DRV_MODULE_NAME         "n2rng"
#define PFX DRV_MODULE_NAME     ": "
#define DRV_MODULE_VERSION      "0.2"
#define DRV_MODULE_RELDATE      "July 27, 2011"

static char version[] =
        DRV_MODULE_NAME ".c:v" DRV_MODULE_VERSION " (" DRV_MODULE_RELDATE ")\n";

MODULE_AUTHOR("David S. Miller (davem@davemloft.net)");
MODULE_DESCRIPTION("Niagara2 RNG driver");
MODULE_LICENSE("GPL");
MODULE_VERSION(DRV_MODULE_VERSION);

/* The Niagara2 RNG provides a 64-bit read-only random number
 * register, plus a control register.  Access to the RNG is
 * virtualized through the hypervisor so that both guests and control
 * nodes can access the device.
 *
 * The entropy source consists of raw entropy sources, each
 * constructed from a voltage controlled oscillator whose phase is
 * jittered by thermal noise sources.
 *
 * The oscillator in each of the three raw entropy sources run at
 * different frequencies.  Normally, all three generator outputs are
 * gathered, xored together, and fed into a CRC circuit, the output of
 * which is the 64-bit read-only register.
 *
 * Some time is necessary for all the necessary entropy to build up
 * such that a full 64-bits of entropy are available in the register.
 * In normal operating mode (RNG_CTL_LFSR is set), the chip implements
 * an interlock which blocks register reads until sufficient entropy
 * is available.
 *
 * A control register is provided for adjusting various aspects of RNG
 * operation, and to enable diagnostic modes.  Each of the three raw
 * entropy sources has an enable bit (RNG_CTL_ES{1,2,3}).  Also
 * provided are fields for controlling the minimum time in cycles
 * between read accesses to the register (RNG_CTL_WAIT, this controls
 * the interlock described in the previous paragraph).
 *
 * The standard setting is to have the mode bit (RNG_CTL_LFSR) set,
 * all three entropy sources enabled, and the interlock time set
 * appropriately.
 *
 * The CRC polynomial used by the chip is:
 *
 * P(X) = x64 + x61 + x57 + x56 + x52 + x51 + x50 + x48 + x47 + x46 +
 *        x43 + x42 + x41 + x39 + x38 + x37 + x35 + x32 + x28 + x25 +
 *        x22 + x21 + x17 + x15 + x13 + x12 + x11 + x7 + x5 + x + 1
 *
 * The RNG_CTL_VCO value of each noise cell must be programmed
 * separately.  This is why 4 control register values must be provided
 * to the hypervisor.  During a write, the hypervisor writes them all,
 * one at a time, to the actual RNG_CTL register.  The first three
 * values are used to setup the desired RNG_CTL_VCO for each entropy
 * source, for example:
 *
 *      control 0: (1 << RNG_CTL_VCO_SHIFT) | RNG_CTL_ES1
 *      control 1: (2 << RNG_CTL_VCO_SHIFT) | RNG_CTL_ES2
 *      control 2: (3 << RNG_CTL_VCO_SHIFT) | RNG_CTL_ES3
 *
 * And then the fourth value sets the final chip state and enables
 * desired.
 */

static int n2rng_hv_err_trans(unsigned long hv_err)
{
        switch (hv_err) {
        case HV_EOK:
                return 0;
        case HV_EWOULDBLOCK:
                return -EAGAIN;
        case HV_ENOACCESS:
                return -EPERM;
        case HV_EIO:
                return -EIO;
        case HV_EBUSY:
                return -EBUSY;
        case HV_EBADALIGN:
        case HV_ENORADDR:
                return -EFAULT;
        default:
                return -EINVAL;
        }
}

static unsigned long n2rng_generic_read_control_v2(unsigned long ra,
                                                   unsigned long unit)
{
        unsigned long hv_err, state, ticks, watchdog_delta, watchdog_status;
        int block = 0, busy = 0;

        while (1) {
                hv_err = sun4v_rng_ctl_read_v2(ra, unit, &state,
                                               &ticks,
                                               &watchdog_delta,
                                               &watchdog_status);
                if (hv_err == HV_EOK)
                        break;

                if (hv_err == HV_EBUSY) {
                        if (++busy >= N2RNG_BUSY_LIMIT)
                                break;

                        udelay(1);
                } else if (hv_err == HV_EWOULDBLOCK) {
                        if (++block >= N2RNG_BLOCK_LIMIT)
                                break;

                        __delay(ticks);
                } else
                        break;
        }

        return hv_err;
}

/* In multi-socket situations, the hypervisor might need to
 * queue up the RNG control register write if it's for a unit
 * that is on a cpu socket other than the one we are executing on.
 *
 * We poll here waiting for a successful read of that control
 * register to make sure the write has been actually performed.
 */
static unsigned long n2rng_control_settle_v2(struct n2rng *np, int unit)
{
        unsigned long ra = __pa(&np->scratch_control[0]);

        return n2rng_generic_read_control_v2(ra, unit);
}

static unsigned long n2rng_write_ctl_one(struct n2rng *np, int unit,
                                         unsigned long state,
                                         unsigned long control_ra,
                                         unsigned long watchdog_timeout,
                                         unsigned long *ticks)
{
        unsigned long hv_err;

        if (np->hvapi_major == 1) {
                hv_err = sun4v_rng_ctl_write_v1(control_ra, state,
                                                watchdog_timeout, ticks);
        } else {
                hv_err = sun4v_rng_ctl_write_v2(control_ra, state,
                                                watchdog_timeout, unit);
                if (hv_err == HV_EOK)
                        hv_err = n2rng_control_settle_v2(np, unit);
                *ticks = N2RNG_ACCUM_CYCLES_DEFAULT;
        }

        return hv_err;
}

static int n2rng_generic_read_data(unsigned long data_ra)
{
        unsigned long ticks, hv_err;
        int block = 0, hcheck = 0;

        while (1) {
                hv_err = sun4v_rng_data_read(data_ra, &ticks);
                if (hv_err == HV_EOK)
                        return 0;

                if (hv_err == HV_EWOULDBLOCK) {
                        if (++block >= N2RNG_BLOCK_LIMIT)
                                return -EWOULDBLOCK;
                        __delay(ticks);
                } else if (hv_err == HV_ENOACCESS) {
                        return -EPERM;
                } else if (hv_err == HV_EIO) {
                        if (++hcheck >= N2RNG_HCHECK_LIMIT)
                                return -EIO;
                        udelay(10000);
                } else
                        return -ENODEV;
        }
}

static unsigned long n2rng_read_diag_data_one(struct n2rng *np,
                                              unsigned long unit,
                                              unsigned long data_ra,
                                              unsigned long data_len,
                                              unsigned long *ticks)
{
        unsigned long hv_err;

        if (np->hvapi_major == 1) {
                hv_err = sun4v_rng_data_read_diag_v1(data_ra, data_len, ticks);
        } else {
                hv_err = sun4v_rng_data_read_diag_v2(data_ra, data_len,
                                                     unit, ticks);
                if (!*ticks)
                        *ticks = N2RNG_ACCUM_CYCLES_DEFAULT;
        }
        return hv_err;
}

static int n2rng_generic_read_diag_data(struct n2rng *np,
                                        unsigned long unit,
                                        unsigned long data_ra,
                                        unsigned long data_len)
{
        unsigned long ticks, hv_err;
        int block = 0;

        while (1) {
                hv_err = n2rng_read_diag_data_one(np, unit,
                                                  data_ra, data_len,
                                                  &ticks);
                if (hv_err == HV_EOK)
                        return 0;

                if (hv_err == HV_EWOULDBLOCK) {
                        if (++block >= N2RNG_BLOCK_LIMIT)
                                return -EWOULDBLOCK;
                        __delay(ticks);
                } else if (hv_err == HV_ENOACCESS) {
                        return -EPERM;
                } else if (hv_err == HV_EIO) {
                        return -EIO;
                } else
                        return -ENODEV;
        }
}


static int n2rng_generic_write_control(struct n2rng *np,
                                       unsigned long control_ra,
                                       unsigned long unit,
                                       unsigned long state)
{
        unsigned long hv_err, ticks;
        int block = 0, busy = 0;

        while (1) {
                hv_err = n2rng_write_ctl_one(np, unit, state, control_ra,
                                             np->wd_timeo, &ticks);
                if (hv_err == HV_EOK)
                        return 0;

                if (hv_err == HV_EWOULDBLOCK) {
                        if (++block >= N2RNG_BLOCK_LIMIT)
                                return -EWOULDBLOCK;
                        __delay(ticks);
                } else if (hv_err == HV_EBUSY) {
                        if (++busy >= N2RNG_BUSY_LIMIT)
                                return -EBUSY;
                        udelay(1);
                } else
                        return -ENODEV;
        }
}

/* Just try to see if we can successfully access the control register
 * of the RNG on the domain on which we are currently executing.
 */
static int n2rng_try_read_ctl(struct n2rng *np)
{
        unsigned long hv_err;
        unsigned long x;

        if (np->hvapi_major == 1) {
                hv_err = sun4v_rng_get_diag_ctl();
        } else {
                /* We purposefully give invalid arguments, HV_NOACCESS
                 * is higher priority than the errors we'd get from
                 * these other cases, and that's the error we are
                 * truly interested in.
                 */
                hv_err = sun4v_rng_ctl_read_v2(0UL, ~0UL, &x, &x, &x, &x);
                switch (hv_err) {
                case HV_EWOULDBLOCK:
                case HV_ENOACCESS:
                        break;
                default:
                        hv_err = HV_EOK;
                        break;
                }
        }

        return n2rng_hv_err_trans(hv_err);
}

#define CONTROL_DEFAULT_BASE            \
        ((2 << RNG_CTL_ASEL_SHIFT) |    \
         (N2RNG_ACCUM_CYCLES_DEFAULT << RNG_CTL_WAIT_SHIFT) |   \
         RNG_CTL_LFSR)

#define CONTROL_DEFAULT_0               \
        (CONTROL_DEFAULT_BASE |         \
         (1 << RNG_CTL_VCO_SHIFT) |     \
         RNG_CTL_ES1)
#define CONTROL_DEFAULT_1               \
        (CONTROL_DEFAULT_BASE |         \
         (2 << RNG_CTL_VCO_SHIFT) |     \
         RNG_CTL_ES2)
#define CONTROL_DEFAULT_2               \
        (CONTROL_DEFAULT_BASE |         \
         (3 << RNG_CTL_VCO_SHIFT) |     \
         RNG_CTL_ES3)
#define CONTROL_DEFAULT_3               \
        (CONTROL_DEFAULT_BASE |         \
         RNG_CTL_ES1 | RNG_CTL_ES2 | RNG_CTL_ES3)

static void n2rng_control_swstate_init(struct n2rng *np)
{
        int i;

        np->flags |= N2RNG_FLAG_CONTROL;

        np->health_check_sec = N2RNG_HEALTH_CHECK_SEC_DEFAULT;
        np->accum_cycles = N2RNG_ACCUM_CYCLES_DEFAULT;
        np->wd_timeo = N2RNG_WD_TIMEO_DEFAULT;

        for (i = 0; i < np->num_units; i++) {
                struct n2rng_unit *up = &np->units[i];

                up->control[0] = CONTROL_DEFAULT_0;
                up->control[1] = CONTROL_DEFAULT_1;
                up->control[2] = CONTROL_DEFAULT_2;
                up->control[3] = CONTROL_DEFAULT_3;
        }

        np->hv_state = HV_RNG_STATE_UNCONFIGURED;
}

static int n2rng_grab_diag_control(struct n2rng *np)
{
        int i, busy_count, err = -ENODEV;

        busy_count = 0;
        for (i = 0; i < 100; i++) {
                err = n2rng_try_read_ctl(np);
                if (err != -EAGAIN)
                        break;

                if (++busy_count > 100) {
                        dev_err(&np->op->dev,
                                "Grab diag control timeout.\n");
                        return -ENODEV;
                }

                udelay(1);
        }

        return err;
}

static int n2rng_init_control(struct n2rng *np)
{
        int err = n2rng_grab_diag_control(np);

        /* Not in the control domain, that's OK we are only a consumer
         * of the RNG data, we don't setup and program it.
         */
        if (err == -EPERM)
                return 0;
        if (err)
                return err;

        n2rng_control_swstate_init(np);

        return 0;
}

static int n2rng_data_read(struct hwrng *rng, u32 *data)
{
        struct n2rng *np = (struct n2rng *) rng->priv;
        unsigned long ra = __pa(&np->test_data);
        int len;

        if (!(np->flags & N2RNG_FLAG_READY)) {
                len = 0;
        } else if (np->flags & N2RNG_FLAG_BUFFER_VALID) {
                np->flags &= ~N2RNG_FLAG_BUFFER_VALID;
                *data = np->buffer;
                len = 4;
        } else {
                int err = n2rng_generic_read_data(ra);
                if (!err) {
                        np->buffer = np->test_data >> 32;
                        *data = np->test_data & 0xffffffff;
                        len = 4;
                } else {
                        dev_err(&np->op->dev, "RNG error, restesting\n");
                        np->flags &= ~N2RNG_FLAG_READY;
                        if (!(np->flags & N2RNG_FLAG_SHUTDOWN))
                                schedule_delayed_work(&np->work, 0);
                        len = 0;
                }
        }

        return len;
}

/* On a guest node, just make sure we can read random data properly.
 * If a control node reboots or reloads it's n2rng driver, this won't
 * work during that time.  So we have to keep probing until the device
 * becomes usable.
 */
static int n2rng_guest_check(struct n2rng *np)
{
        unsigned long ra = __pa(&np->test_data);

        return n2rng_generic_read_data(ra);
}

static int n2rng_entropy_diag_read(struct n2rng *np, unsigned long unit,
                                   u64 *pre_control, u64 pre_state,
                                   u64 *buffer, unsigned long buf_len,
                                   u64 *post_control, u64 post_state)
{
        unsigned long post_ctl_ra = __pa(post_control);
        unsigned long pre_ctl_ra = __pa(pre_control);
        unsigned long buffer_ra = __pa(buffer);
        int err;

        err = n2rng_generic_write_control(np, pre_ctl_ra, unit, pre_state);
        if (err)
                return err;

        err = n2rng_generic_read_diag_data(np, unit,
                                           buffer_ra, buf_len);

        (void) n2rng_generic_write_control(np, post_ctl_ra, unit,
                                           post_state);

        return err;
}

static u64 advance_polynomial(u64 poly, u64 val, int count)
{
        int i;

        for (i = 0; i < count; i++) {
                int highbit_set = ((s64)val < 0);

                val <<= 1;
                if (highbit_set)
                        val ^= poly;
        }

        return val;
}

static int n2rng_test_buffer_find(struct n2rng *np, u64 val)
{
        int i, count = 0;

        /* Purposefully skip over the first word.  */
        for (i = 1; i < SELFTEST_BUFFER_WORDS; i++) {
                if (np->test_buffer[i] == val)
                        count++;
        }
        return count;
}

static void n2rng_dump_test_buffer(struct n2rng *np)
{
        int i;

        for (i = 0; i < SELFTEST_BUFFER_WORDS; i++)
                dev_err(&np->op->dev, "Test buffer slot %d [0x%016llx]\n",
                        i, np->test_buffer[i]);
}

static int n2rng_check_selftest_buffer(struct n2rng *np, unsigned long unit)
{
        u64 val = SELFTEST_VAL;
        int err, matches, limit;

        matches = 0;
        for (limit = 0; limit < SELFTEST_LOOPS_MAX; limit++) {
                matches += n2rng_test_buffer_find(np, val);
                if (matches >= SELFTEST_MATCH_GOAL)
                        break;
                val = advance_polynomial(SELFTEST_POLY, val, 1);
        }

        err = 0;
        if (limit >= SELFTEST_LOOPS_MAX) {
                err = -ENODEV;
                dev_err(&np->op->dev, "Selftest failed on unit %lu\n", unit);
                n2rng_dump_test_buffer(np);
        } else
                dev_info(&np->op->dev, "Selftest passed on unit %lu\n", unit);

        return err;
}

static int n2rng_control_selftest(struct n2rng *np, unsigned long unit)
{
        int err;

        np->test_control[0] = (0x2 << RNG_CTL_ASEL_SHIFT);
        np->test_control[1] = (0x2 << RNG_CTL_ASEL_SHIFT);
        np->test_control[2] = (0x2 << RNG_CTL_ASEL_SHIFT);
        np->test_control[3] = ((0x2 << RNG_CTL_ASEL_SHIFT) |
                               RNG_CTL_LFSR |
                               ((SELFTEST_TICKS - 2) << RNG_CTL_WAIT_SHIFT));


        err = n2rng_entropy_diag_read(np, unit, np->test_control,
                                      HV_RNG_STATE_HEALTHCHECK,
                                      np->test_buffer,
                                      sizeof(np->test_buffer),
                                      &np->units[unit].control[0],
                                      np->hv_state);
        if (err)
                return err;

        return n2rng_check_selftest_buffer(np, unit);
}

static int n2rng_control_check(struct n2rng *np)
{
        int i;

        for (i = 0; i < np->num_units; i++) {
                int err = n2rng_control_selftest(np, i);
                if (err)
                        return err;
        }
        return 0;
}

/* The sanity checks passed, install the final configuration into the
 * chip, it's ready to use.
 */
static int n2rng_control_configure_units(struct n2rng *np)
{
        int unit, err;

        err = 0;
        for (unit = 0; unit < np->num_units; unit++) {
                struct n2rng_unit *up = &np->units[unit];
                unsigned long ctl_ra = __pa(&up->control[0]);
                int esrc;
                u64 base;

                base = ((np->accum_cycles << RNG_CTL_WAIT_SHIFT) |
                        (2 << RNG_CTL_ASEL_SHIFT) |
                        RNG_CTL_LFSR);

                /* XXX This isn't the best.  We should fetch a bunch
                 * XXX of words using each entropy source combined XXX
                 * with each VCO setting, and see which combinations
                 * XXX give the best random data.
                 */
                for (esrc = 0; esrc < 3; esrc++)
                        up->control[esrc] = base |
                                (esrc << RNG_CTL_VCO_SHIFT) |
                                (RNG_CTL_ES1 << esrc);

                up->control[3] = base |
                        (RNG_CTL_ES1 | RNG_CTL_ES2 | RNG_CTL_ES3);

                err = n2rng_generic_write_control(np, ctl_ra, unit,
                                                  HV_RNG_STATE_CONFIGURED);
                if (err)
                        break;
        }

        return err;
}

static void n2rng_work(struct work_struct *work)
{
        struct n2rng *np = container_of(work, struct n2rng, work.work);
        int err = 0;

        if (!(np->flags & N2RNG_FLAG_CONTROL)) {
                err = n2rng_guest_check(np);
        } else {
                preempt_disable();
                err = n2rng_control_check(np);
                preempt_enable();

                if (!err)
                        err = n2rng_control_configure_units(np);
        }

        if (!err) {
                np->flags |= N2RNG_FLAG_READY;
                dev_info(&np->op->dev, "RNG ready\n");
        }

        if (err && !(np->flags & N2RNG_FLAG_SHUTDOWN))
                schedule_delayed_work(&np->work, HZ * 2);
}

static void n2rng_driver_version(void)
{
        static int n2rng_version_printed;

        if (n2rng_version_printed++ == 0)
                pr_info("%s", version);
}

static const struct of_device_id n2rng_match[];
static int n2rng_probe(struct platform_device *op)
{
        const struct of_device_id *match;
        int multi_capable;
        int err = -ENOMEM;
        struct n2rng *np;

        match = of_match_device(n2rng_match, &op->dev);
        if (!match)
                return -EINVAL;
        multi_capable = (match->data != NULL);

        n2rng_driver_version();
        np = devm_kzalloc(&op->dev, sizeof(*np), GFP_KERNEL);
        if (!np)
                goto out;
        np->op = op;

        INIT_DELAYED_WORK(&np->work, n2rng_work);

        if (multi_capable)
                np->flags |= N2RNG_FLAG_MULTI;

        err = -ENODEV;
        np->hvapi_major = 2;
        if (sun4v_hvapi_register(HV_GRP_RNG,
                                 np->hvapi_major,
                                 &np->hvapi_minor)) {
                np->hvapi_major = 1;
                if (sun4v_hvapi_register(HV_GRP_RNG,
                                         np->hvapi_major,
                                         &np->hvapi_minor)) {
                        dev_err(&op->dev, "Cannot register suitable "
                                "HVAPI version.\n");
                        goto out;
                }
        }

        if (np->flags & N2RNG_FLAG_MULTI) {
                if (np->hvapi_major < 2) {
                        dev_err(&op->dev, "multi-unit-capable RNG requires "
                                "HVAPI major version 2 or later, got %lu\n",
                                np->hvapi_major);
                        goto out_hvapi_unregister;
                }
                np->num_units = of_getintprop_default(op->dev.of_node,
                                                      "rng-#units", 0);
                if (!np->num_units) {
                        dev_err(&op->dev, "VF RNG lacks rng-#units property\n");
                        goto out_hvapi_unregister;
                }
        } else
                np->num_units = 1;

        dev_info(&op->dev, "Registered RNG HVAPI major %lu minor %lu\n",
                 np->hvapi_major, np->hvapi_minor);

        np->units = devm_kzalloc(&op->dev,
                                 sizeof(struct n2rng_unit) * np->num_units,
                                 GFP_KERNEL);
        err = -ENOMEM;
        if (!np->units)
                goto out_hvapi_unregister;

        err = n2rng_init_control(np);
        if (err)
                goto out_hvapi_unregister;

        dev_info(&op->dev, "Found %s RNG, units: %d\n",
                 ((np->flags & N2RNG_FLAG_MULTI) ?
                  "multi-unit-capable" : "single-unit"),
                 np->num_units);

        np->hwrng.name = "n2rng";
        np->hwrng.data_read = n2rng_data_read;
        np->hwrng.priv = (unsigned long) np;

        err = hwrng_register(&np->hwrng);
        if (err)
                goto out_hvapi_unregister;

        platform_set_drvdata(op, np);

        schedule_delayed_work(&np->work, 0);

        return 0;

out_hvapi_unregister:
        sun4v_hvapi_unregister(HV_GRP_RNG);

out:
        return err;
}

static int n2rng_remove(struct platform_device *op)
{
        struct n2rng *np = platform_get_drvdata(op);

        np->flags |= N2RNG_FLAG_SHUTDOWN;

        cancel_delayed_work_sync(&np->work);

        hwrng_unregister(&np->hwrng);

        sun4v_hvapi_unregister(HV_GRP_RNG);

        return 0;
}

static const struct of_device_id n2rng_match[] = {
        {
                .name           = "random-number-generator",
                .compatible     = "SUNW,n2-rng",
        },
        {
                .name           = "random-number-generator",
                .compatible     = "SUNW,vf-rng",
                .data           = (void *) 1,
        },
        {
                .name           = "random-number-generator",
                .compatible     = "SUNW,kt-rng",
                .data           = (void *) 1,
        },
        {
                .name           = "random-number-generator",
                .compatible     = "ORCL,m4-rng",
                .data           = (void *) 1,
        },
        {
                .name           = "random-number-generator",
                .compatible     = "ORCL,m7-rng",
                .data           = (void *) 1,
        },
        {},
};
MODULE_DEVICE_TABLE(of, n2rng_match);

static struct platform_driver n2rng_driver = {
        .driver = {
                .name = "n2rng",
                .of_match_table = n2rng_match,
        },
        .probe          = n2rng_probe,
        .remove         = n2rng_remove,
};

module_platform_driver(n2rng_driver);