/*
 * RNG driver for VIA RNGs
 *
 * Copyright 2005 (c) MontaVista Software, Inc.
 *
 * with the majority of the code coming from:
 *
 * Hardware driver for the Intel/AMD/VIA Random Number Generators (RNG)
 * (c) Copyright 2003 Red Hat Inc <jgarzik@redhat.com>
 *
 * derived from
 *
 * Hardware driver for the AMD 768 Random Number Generator (RNG)
 * (c) Copyright 2001 Red Hat Inc
 *
 * derived from
 *
 * Hardware driver for Intel i810 Random Number Generator (RNG)
 * Copyright 2000,2001 Jeff Garzik <jgarzik@pobox.com>
 * Copyright 2000,2001 Philipp Rumpf <prumpf@mandrakesoft.com>
 *
 * This file is licensed under  the terms of the GNU General Public
 * License version 2. This program is licensed "as is" without any
 * warranty of any kind, whether express or implied.
 */

#include <crypto/padlock.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/hw_random.h>
#include <linux/delay.h>
#include <asm/cpu_device_id.h>
#include <asm/io.h>
#include <asm/msr.h>
#include <asm/cpufeature.h>
#include <asm/fpu/api.h>




enum {
        VIA_STRFILT_CNT_SHIFT   = 16,
        VIA_STRFILT_FAIL        = (1 << 15),
        VIA_STRFILT_ENABLE      = (1 << 14),
        VIA_RAWBITS_ENABLE      = (1 << 13),
        VIA_RNG_ENABLE          = (1 << 6),
        VIA_NOISESRC1           = (1 << 8),
        VIA_NOISESRC2           = (1 << 9),
        VIA_XSTORE_CNT_MASK     = 0x0F,

        VIA_RNG_CHUNK_8         = 0x00, /* 64 rand bits, 64 stored bits */
        VIA_RNG_CHUNK_4         = 0x01, /* 32 rand bits, 32 stored bits */
        VIA_RNG_CHUNK_4_MASK    = 0xFFFFFFFF,
        VIA_RNG_CHUNK_2         = 0x02, /* 16 rand bits, 32 stored bits */
        VIA_RNG_CHUNK_2_MASK    = 0xFFFF,
        VIA_RNG_CHUNK_1         = 0x03, /* 8 rand bits, 32 stored bits */
        VIA_RNG_CHUNK_1_MASK    = 0xFF,
};

/*
 * Investigate using the 'rep' prefix to obtain 32 bits of random data
 * in one insn.  The upside is potentially better performance.  The
 * downside is that the instruction becomes no longer atomic.  Due to
 * this, just like familiar issues with /dev/random itself, the worst
 * case of a 'rep xstore' could potentially pause a cpu for an
 * unreasonably long time.  In practice, this condition would likely
 * only occur when the hardware is failing.  (or so we hope :))
 *
 * Another possible performance boost may come from simply buffering
 * until we have 4 bytes, thus returning a u32 at a time,
 * instead of the current u8-at-a-time.
 *
 * Padlock instructions can generate a spurious DNA fault, but the
 * kernel doesn't use CR0.TS, so this doesn't matter.
 */

static inline u32 xstore(u32 *addr, u32 edx_in)
{
        u32 eax_out;

        asm(".byte 0x0F,0xA7,0xC0 /* xstore %%edi (addr=%0) */"
                : "=m" (*addr), "=a" (eax_out), "+d" (edx_in), "+D" (addr));

        return eax_out;
}

static int via_rng_data_present(struct hwrng *rng, int wait)
{
        char buf[16 + PADLOCK_ALIGNMENT - STACK_ALIGN] __attribute__
                ((aligned(STACK_ALIGN)));
        u32 *via_rng_datum = (u32 *)PTR_ALIGN(&buf[0], PADLOCK_ALIGNMENT);
        u32 bytes_out;
        int i;

        /* We choose the recommended 1-byte-per-instruction RNG rate,
         * for greater randomness at the expense of speed.  Larger
         * values 2, 4, or 8 bytes-per-instruction yield greater
         * speed at lesser randomness.
         *
         * If you change this to another VIA_CHUNK_n, you must also
         * change the ->n_bytes values in rng_vendor_ops[] tables.
         * VIA_CHUNK_8 requires further code changes.
         *
         * A copy of MSR_VIA_RNG is placed in eax_out when xstore
         * completes.
         */

        for (i = 0; i < 20; i++) {
                *via_rng_datum = 0; /* paranoia, not really necessary */
                bytes_out = xstore(via_rng_datum, VIA_RNG_CHUNK_1);
                bytes_out &= VIA_XSTORE_CNT_MASK;
                if (bytes_out || !wait)
                        break;
                udelay(10);
        }
        rng->priv = *via_rng_datum;
        return bytes_out ? 1 : 0;
}

static int via_rng_data_read(struct hwrng *rng, u32 *data)
{
        u32 via_rng_datum = (u32)rng->priv;

        *data = via_rng_datum;

        return 1;
}

static int via_rng_init(struct hwrng *rng)
{
        struct cpuinfo_x86 *c = &cpu_data(0);
        u32 lo, hi, old_lo;

        /* VIA Nano CPUs don't have the MSR_VIA_RNG anymore.  The RNG
         * is always enabled if CPUID rng_en is set.  There is no
         * RNG configuration like it used to be the case in this
         * register */
        if (((c->x86 == 6) && (c->x86_model >= 0x0f))  || (c->x86 > 6)){
                if (!boot_cpu_has(X86_FEATURE_XSTORE_EN)) {
                        pr_err(PFX "can't enable hardware RNG "
                                "if XSTORE is not enabled\n");
                        return -ENODEV;
                }
                return 0;
        }

        /* Control the RNG via MSR.  Tread lightly and pay very close
         * close attention to values written, as the reserved fields
         * are documented to be "undefined and unpredictable"; but it
         * does not say to write them as zero, so I make a guess that
         * we restore the values we find in the register.
         */
        rdmsr(MSR_VIA_RNG, lo, hi);

        old_lo = lo;
        lo &= ~(0x7f << VIA_STRFILT_CNT_SHIFT);
        lo &= ~VIA_XSTORE_CNT_MASK;
        lo &= ~(VIA_STRFILT_ENABLE | VIA_STRFILT_FAIL | VIA_RAWBITS_ENABLE);
        lo |= VIA_RNG_ENABLE;
        lo |= VIA_NOISESRC1;

        /* Enable secondary noise source on CPUs where it is present. */

        /* Nehemiah stepping 8 and higher */
        if ((c->x86_model == 9) && (c->x86_stepping > 7))
                lo |= VIA_NOISESRC2;

        /* Esther */
        if (c->x86_model >= 10)
                lo |= VIA_NOISESRC2;

        if (lo != old_lo)
                wrmsr(MSR_VIA_RNG, lo, hi);

        /* perhaps-unnecessary sanity check; remove after testing if
           unneeded */
        rdmsr(MSR_VIA_RNG, lo, hi);
        if ((lo & VIA_RNG_ENABLE) == 0) {
                pr_err(PFX "cannot enable VIA C3 RNG, aborting\n");
                return -ENODEV;
        }

        return 0;
}


static struct hwrng via_rng = {
        .name           = "via",
        .init           = via_rng_init,
        .data_present   = via_rng_data_present,
        .data_read      = via_rng_data_read,
};


static int __init mod_init(void)
{
        int err;

        if (!boot_cpu_has(X86_FEATURE_XSTORE))
                return -ENODEV;

        pr_info("VIA RNG detected\n");
        err = hwrng_register(&via_rng);
        if (err) {
                pr_err(PFX "RNG registering failed (%d)\n",
                       err);
                goto out;
        }
out:
        return err;
}

static void __exit mod_exit(void)
{
        hwrng_unregister(&via_rng);
}

module_init(mod_init);
module_exit(mod_exit);

static struct x86_cpu_id __maybe_unused via_rng_cpu_id[] = {
        X86_FEATURE_MATCH(X86_FEATURE_XSTORE),
        {}
};

MODULE_DESCRIPTION("H/W RNG driver for VIA CPU with PadLock");
MODULE_LICENSE("GPL");
MODULE_DEVICE_TABLE(x86cpu, via_rng_cpu_id);