Michael Buesch | 1352336 | 2006-06-26 00:25:02 -0700 | [diff] [blame] | 1 | /* |
| 2 | * RNG driver for VIA RNGs |
| 3 | * |
| 4 | * Copyright 2005 (c) MontaVista Software, Inc. |
| 5 | * |
| 6 | * with the majority of the code coming from: |
| 7 | * |
| 8 | * Hardware driver for the Intel/AMD/VIA Random Number Generators (RNG) |
| 9 | * (c) Copyright 2003 Red Hat Inc <jgarzik@redhat.com> |
| 10 | * |
| 11 | * derived from |
| 12 | * |
| 13 | * Hardware driver for the AMD 768 Random Number Generator (RNG) |
| 14 | * (c) Copyright 2001 Red Hat Inc <alan@redhat.com> |
| 15 | * |
| 16 | * derived from |
| 17 | * |
| 18 | * Hardware driver for Intel i810 Random Number Generator (RNG) |
| 19 | * Copyright 2000,2001 Jeff Garzik <jgarzik@pobox.com> |
| 20 | * Copyright 2000,2001 Philipp Rumpf <prumpf@mandrakesoft.com> |
| 21 | * |
| 22 | * This file is licensed under the terms of the GNU General Public |
| 23 | * License version 2. This program is licensed "as is" without any |
| 24 | * warranty of any kind, whether express or implied. |
| 25 | */ |
| 26 | |
| 27 | #include <linux/module.h> |
| 28 | #include <linux/kernel.h> |
Michael Buesch | 1352336 | 2006-06-26 00:25:02 -0700 | [diff] [blame] | 29 | #include <linux/hw_random.h> |
Patrick McHardy | 984e976 | 2007-11-21 12:24:45 +0800 | [diff] [blame] | 30 | #include <linux/delay.h> |
Michael Buesch | 1352336 | 2006-06-26 00:25:02 -0700 | [diff] [blame] | 31 | #include <asm/io.h> |
| 32 | #include <asm/msr.h> |
| 33 | #include <asm/cpufeature.h> |
| 34 | |
| 35 | |
| 36 | #define PFX KBUILD_MODNAME ": " |
| 37 | |
| 38 | |
| 39 | enum { |
| 40 | VIA_STRFILT_CNT_SHIFT = 16, |
| 41 | VIA_STRFILT_FAIL = (1 << 15), |
| 42 | VIA_STRFILT_ENABLE = (1 << 14), |
| 43 | VIA_RAWBITS_ENABLE = (1 << 13), |
| 44 | VIA_RNG_ENABLE = (1 << 6), |
Dave Jones | 11025e8 | 2008-02-06 01:37:13 -0800 | [diff] [blame^] | 45 | VIA_NOISESRC1 = (1 << 8), |
| 46 | VIA_NOISESRC2 = (1 << 9), |
Michael Buesch | 1352336 | 2006-06-26 00:25:02 -0700 | [diff] [blame] | 47 | VIA_XSTORE_CNT_MASK = 0x0F, |
| 48 | |
| 49 | VIA_RNG_CHUNK_8 = 0x00, /* 64 rand bits, 64 stored bits */ |
| 50 | VIA_RNG_CHUNK_4 = 0x01, /* 32 rand bits, 32 stored bits */ |
| 51 | VIA_RNG_CHUNK_4_MASK = 0xFFFFFFFF, |
| 52 | VIA_RNG_CHUNK_2 = 0x02, /* 16 rand bits, 32 stored bits */ |
| 53 | VIA_RNG_CHUNK_2_MASK = 0xFFFF, |
| 54 | VIA_RNG_CHUNK_1 = 0x03, /* 8 rand bits, 32 stored bits */ |
| 55 | VIA_RNG_CHUNK_1_MASK = 0xFF, |
| 56 | }; |
| 57 | |
| 58 | /* |
| 59 | * Investigate using the 'rep' prefix to obtain 32 bits of random data |
| 60 | * in one insn. The upside is potentially better performance. The |
| 61 | * downside is that the instruction becomes no longer atomic. Due to |
| 62 | * this, just like familiar issues with /dev/random itself, the worst |
| 63 | * case of a 'rep xstore' could potentially pause a cpu for an |
| 64 | * unreasonably long time. In practice, this condition would likely |
| 65 | * only occur when the hardware is failing. (or so we hope :)) |
| 66 | * |
| 67 | * Another possible performance boost may come from simply buffering |
| 68 | * until we have 4 bytes, thus returning a u32 at a time, |
| 69 | * instead of the current u8-at-a-time. |
| 70 | */ |
| 71 | |
| 72 | static inline u32 xstore(u32 *addr, u32 edx_in) |
| 73 | { |
| 74 | u32 eax_out; |
| 75 | |
| 76 | asm(".byte 0x0F,0xA7,0xC0 /* xstore %%edi (addr=%0) */" |
| 77 | :"=m"(*addr), "=a"(eax_out) |
| 78 | :"D"(addr), "d"(edx_in)); |
| 79 | |
| 80 | return eax_out; |
| 81 | } |
| 82 | |
Patrick McHardy | 984e976 | 2007-11-21 12:24:45 +0800 | [diff] [blame] | 83 | static int via_rng_data_present(struct hwrng *rng, int wait) |
Michael Buesch | 1352336 | 2006-06-26 00:25:02 -0700 | [diff] [blame] | 84 | { |
| 85 | u32 bytes_out; |
| 86 | u32 *via_rng_datum = (u32 *)(&rng->priv); |
Patrick McHardy | 984e976 | 2007-11-21 12:24:45 +0800 | [diff] [blame] | 87 | int i; |
Michael Buesch | 1352336 | 2006-06-26 00:25:02 -0700 | [diff] [blame] | 88 | |
| 89 | /* We choose the recommended 1-byte-per-instruction RNG rate, |
| 90 | * for greater randomness at the expense of speed. Larger |
| 91 | * values 2, 4, or 8 bytes-per-instruction yield greater |
| 92 | * speed at lesser randomness. |
| 93 | * |
| 94 | * If you change this to another VIA_CHUNK_n, you must also |
| 95 | * change the ->n_bytes values in rng_vendor_ops[] tables. |
| 96 | * VIA_CHUNK_8 requires further code changes. |
| 97 | * |
| 98 | * A copy of MSR_VIA_RNG is placed in eax_out when xstore |
| 99 | * completes. |
| 100 | */ |
| 101 | |
Patrick McHardy | 984e976 | 2007-11-21 12:24:45 +0800 | [diff] [blame] | 102 | for (i = 0; i < 20; i++) { |
| 103 | *via_rng_datum = 0; /* paranoia, not really necessary */ |
| 104 | bytes_out = xstore(via_rng_datum, VIA_RNG_CHUNK_1); |
| 105 | bytes_out &= VIA_XSTORE_CNT_MASK; |
| 106 | if (bytes_out || !wait) |
| 107 | break; |
| 108 | udelay(10); |
| 109 | } |
| 110 | return bytes_out ? 1 : 0; |
Michael Buesch | 1352336 | 2006-06-26 00:25:02 -0700 | [diff] [blame] | 111 | } |
| 112 | |
| 113 | static int via_rng_data_read(struct hwrng *rng, u32 *data) |
| 114 | { |
| 115 | u32 via_rng_datum = (u32)rng->priv; |
| 116 | |
| 117 | *data = via_rng_datum; |
| 118 | |
| 119 | return 1; |
| 120 | } |
| 121 | |
| 122 | static int via_rng_init(struct hwrng *rng) |
| 123 | { |
Dave Jones | 11025e8 | 2008-02-06 01:37:13 -0800 | [diff] [blame^] | 124 | struct cpuinfo_x86 *c = &cpu_data(0); |
Michael Buesch | 1352336 | 2006-06-26 00:25:02 -0700 | [diff] [blame] | 125 | u32 lo, hi, old_lo; |
| 126 | |
| 127 | /* Control the RNG via MSR. Tread lightly and pay very close |
| 128 | * close attention to values written, as the reserved fields |
| 129 | * are documented to be "undefined and unpredictable"; but it |
| 130 | * does not say to write them as zero, so I make a guess that |
| 131 | * we restore the values we find in the register. |
| 132 | */ |
| 133 | rdmsr(MSR_VIA_RNG, lo, hi); |
| 134 | |
| 135 | old_lo = lo; |
| 136 | lo &= ~(0x7f << VIA_STRFILT_CNT_SHIFT); |
| 137 | lo &= ~VIA_XSTORE_CNT_MASK; |
| 138 | lo &= ~(VIA_STRFILT_ENABLE | VIA_STRFILT_FAIL | VIA_RAWBITS_ENABLE); |
| 139 | lo |= VIA_RNG_ENABLE; |
Dave Jones | 11025e8 | 2008-02-06 01:37:13 -0800 | [diff] [blame^] | 140 | lo |= VIA_NOISESRC1; |
| 141 | |
| 142 | /* Enable secondary noise source on CPUs where it is present. */ |
| 143 | |
| 144 | /* Nehemiah stepping 8 and higher */ |
| 145 | if ((c->x86_model == 9) && (c->x86_mask > 7)) |
| 146 | lo |= VIA_NOISESRC2; |
| 147 | |
| 148 | /* Esther */ |
| 149 | if (c->x86_model >= 10) |
| 150 | lo |= VIA_NOISESRC2; |
Michael Buesch | 1352336 | 2006-06-26 00:25:02 -0700 | [diff] [blame] | 151 | |
| 152 | if (lo != old_lo) |
| 153 | wrmsr(MSR_VIA_RNG, lo, hi); |
| 154 | |
| 155 | /* perhaps-unnecessary sanity check; remove after testing if |
| 156 | unneeded */ |
| 157 | rdmsr(MSR_VIA_RNG, lo, hi); |
| 158 | if ((lo & VIA_RNG_ENABLE) == 0) { |
| 159 | printk(KERN_ERR PFX "cannot enable VIA C3 RNG, aborting\n"); |
| 160 | return -ENODEV; |
| 161 | } |
| 162 | |
| 163 | return 0; |
| 164 | } |
| 165 | |
| 166 | |
| 167 | static struct hwrng via_rng = { |
| 168 | .name = "via", |
| 169 | .init = via_rng_init, |
| 170 | .data_present = via_rng_data_present, |
| 171 | .data_read = via_rng_data_read, |
| 172 | }; |
| 173 | |
| 174 | |
| 175 | static int __init mod_init(void) |
| 176 | { |
| 177 | int err; |
| 178 | |
| 179 | if (!cpu_has_xstore) |
| 180 | return -ENODEV; |
| 181 | printk(KERN_INFO "VIA RNG detected\n"); |
| 182 | err = hwrng_register(&via_rng); |
| 183 | if (err) { |
| 184 | printk(KERN_ERR PFX "RNG registering failed (%d)\n", |
| 185 | err); |
| 186 | goto out; |
| 187 | } |
| 188 | out: |
| 189 | return err; |
| 190 | } |
| 191 | |
| 192 | static void __exit mod_exit(void) |
| 193 | { |
| 194 | hwrng_unregister(&via_rng); |
| 195 | } |
| 196 | |
Michael Buesch | 56fb5fe | 2007-01-10 23:15:43 -0800 | [diff] [blame] | 197 | module_init(mod_init); |
Michael Buesch | 1352336 | 2006-06-26 00:25:02 -0700 | [diff] [blame] | 198 | module_exit(mod_exit); |
| 199 | |
| 200 | MODULE_DESCRIPTION("H/W RNG driver for VIA chipsets"); |
| 201 | MODULE_LICENSE("GPL"); |