/*
* 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 <alan@redhat.com>
*
* 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 <linux/module.h>
#include <linux/kernel.h>
#include <linux/hw_random.h>
#include <linux/delay.h>
#include <asm/io.h>
#include <asm/msr.h>
#include <asm/cpufeature.h>
#define PFX KBUILD_MODNAME ": "
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_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.
*/
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"(addr), "d"(edx_in));
return eax_out;
}
static int via_rng_data_present(struct hwrng *rng, int wait)
{
u32 bytes_out;
u32 *via_rng_datum = (u32 *)(&rng->priv);
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);
}
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)
{
u32 lo, hi, old_lo;
/* 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;
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) {
printk(KERN_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 (!cpu_has_xstore)
return -ENODEV;
printk(KERN_INFO "VIA RNG detected\n");
err = hwrng_register(&via_rng);
if (err) {
printk(KERN_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);
MODULE_DESCRIPTION("H/W RNG driver for VIA chipsets");
MODULE_LICENSE("GPL");
