diff options
Diffstat (limited to 'drivers/char/hw_random/via-rng.c')
| -rw-r--r-- | drivers/char/hw_random/via-rng.c | 183 |
1 files changed, 183 insertions, 0 deletions
diff --git a/drivers/char/hw_random/via-rng.c b/drivers/char/hw_random/via-rng.c new file mode 100644 index 000000000000..0e786b617bb8 --- /dev/null +++ b/drivers/char/hw_random/via-rng.c @@ -0,0 +1,183 @@ +/* + * 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/pci.h> +#include <linux/hw_random.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) +{ + u32 bytes_out; + u32 *via_rng_datum = (u32 *)(&rng->priv); + + /* 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. + */ + + *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 == 0) + return 0; + return 1; +} + +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); +} + +subsys_initcall(mod_init); +module_exit(mod_exit); + +MODULE_DESCRIPTION("H/W RNG driver for VIA chipsets"); +MODULE_LICENSE("GPL"); |