// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright 2013, Michael Ellerman, IBM Corporation.
 */

#define pr_fmt(fmt)     "powernv-rng: " fmt

#include <linux/kernel.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_platform.h>
#include <linux/slab.h>
#include <linux/smp.h>
#include <asm/archrandom.h>
#include <asm/cputable.h>
#include <asm/io.h>
#include <asm/prom.h>
#include <asm/machdep.h>
#include <asm/smp.h>
#include "powernv.h"

#define DARN_ERR 0xFFFFFFFFFFFFFFFFul

struct pnv_rng {
        void __iomem *regs;
        void __iomem *regs_real;
        unsigned long mask;
};

static DEFINE_PER_CPU(struct pnv_rng *, pnv_rng);

static unsigned long rng_whiten(struct pnv_rng *rng, unsigned long val)
{
        unsigned long parity;

        /* Calculate the parity of the value */
        asm (".machine push;   \
              .machine power7; \
              popcntd %0,%1;   \
              .machine pop;"
             : "=r" (parity) : "r" (val));

        /* xor our value with the previous mask */
        val ^= rng->mask;

        /* update the mask based on the parity of this value */
        rng->mask = (rng->mask << 1) | (parity & 1);

        return val;
}

static int pnv_get_random_darn(unsigned long *v)
{
        unsigned long val;

        /* Using DARN with L=1 - 64-bit conditioned random number */
        asm volatile(PPC_DARN(%0, 1) : "=r"(val));

        if (val == DARN_ERR)
                return 0;

        *v = val;

        return 1;
}

static int __init initialise_darn(void)
{
        unsigned long val;
        int i;

        if (!cpu_has_feature(CPU_FTR_ARCH_300))
                return -ENODEV;

        for (i = 0; i < 10; i++) {
                if (pnv_get_random_darn(&val)) {
                        ppc_md.get_random_seed = pnv_get_random_darn;
                        return 0;
                }
        }
        return -EIO;
}

int pnv_get_random_long(unsigned long *v)
{
        struct pnv_rng *rng;

        if (mfmsr() & MSR_DR) {
                rng = get_cpu_var(pnv_rng);
                *v = rng_whiten(rng, in_be64(rng->regs));
                put_cpu_var(rng);
        } else {
                rng = raw_cpu_read(pnv_rng);
                *v = rng_whiten(rng, __raw_rm_readq(rng->regs_real));
        }
        return 1;
}
EXPORT_SYMBOL_GPL(pnv_get_random_long);

static __init void rng_init_per_cpu(struct pnv_rng *rng,
                                    struct device_node *dn)
{
        int chip_id, cpu;

        chip_id = of_get_ibm_chip_id(dn);
        if (chip_id == -1)
                pr_warn("No ibm,chip-id found for %pOF.\n", dn);

        for_each_possible_cpu(cpu) {
                if (per_cpu(pnv_rng, cpu) == NULL ||
                    cpu_to_chip_id(cpu) == chip_id) {
                        per_cpu(pnv_rng, cpu) = rng;
                }
        }
}

static __init int rng_create(struct device_node *dn)
{
        struct pnv_rng *rng;
        struct resource res;
        unsigned long val;

        rng = kzalloc_obj(*rng);
        if (!rng)
                return -ENOMEM;

        if (of_address_to_resource(dn, 0, &res)) {
                kfree(rng);
                return -ENXIO;
        }

        rng->regs_real = (void __iomem *)res.start;

        rng->regs = of_iomap(dn, 0);
        if (!rng->regs) {
                kfree(rng);
                return -ENXIO;
        }

        val = in_be64(rng->regs);
        rng->mask = val;

        rng_init_per_cpu(rng, dn);

        ppc_md.get_random_seed = pnv_get_random_long;

        return 0;
}

static int __init pnv_get_random_long_early(unsigned long *v)
{
        struct device_node *dn;

        if (!slab_is_available())
                return 0;

        if (cmpxchg(&ppc_md.get_random_seed, pnv_get_random_long_early,
                    NULL) != pnv_get_random_long_early)
                return 0;

        for_each_compatible_node(dn, NULL, "ibm,power-rng")
                rng_create(dn);

        if (!ppc_md.get_random_seed)
                return 0;
        return ppc_md.get_random_seed(v);
}

void __init pnv_rng_init(void)
{
        struct device_node *dn;

        /* Prefer darn over the rest. */
        if (!initialise_darn())
                return;

        dn = of_find_compatible_node(NULL, NULL, "ibm,power-rng");
        if (dn)
                ppc_md.get_random_seed = pnv_get_random_long_early;

        of_node_put(dn);
}

static int __init pnv_rng_late_init(void)
{
        struct device_node *dn;
        unsigned long v;

        /* In case it wasn't called during init for some other reason. */
        if (ppc_md.get_random_seed == pnv_get_random_long_early)
                pnv_get_random_long_early(&v);

        if (ppc_md.get_random_seed == pnv_get_random_long) {
                for_each_compatible_node(dn, NULL, "ibm,power-rng")
                        of_platform_device_create(dn, NULL, NULL);
        }

        return 0;
}
machine_subsys_initcall(powernv, pnv_rng_late_init);