Linux 2.6.20.7
[linux/fpc-iii.git] / drivers / char / hw_random / via-rng.c
blob9ebf84d18655eb06e48ccc9cab5cb8473bf6b77a
1 /*
2 * RNG driver for VIA RNGs
4 * Copyright 2005 (c) MontaVista Software, Inc.
6 * with the majority of the code coming from:
8 * Hardware driver for the Intel/AMD/VIA Random Number Generators (RNG)
9 * (c) Copyright 2003 Red Hat Inc <jgarzik@redhat.com>
11 * derived from
13 * Hardware driver for the AMD 768 Random Number Generator (RNG)
14 * (c) Copyright 2001 Red Hat Inc <alan@redhat.com>
16 * derived from
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>
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.
27 #include <linux/module.h>
28 #include <linux/kernel.h>
29 #include <linux/pci.h>
30 #include <linux/hw_random.h>
31 #include <asm/io.h>
32 #include <asm/msr.h>
33 #include <asm/cpufeature.h>
36 #define PFX KBUILD_MODNAME ": "
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),
45 VIA_XSTORE_CNT_MASK = 0x0F,
47 VIA_RNG_CHUNK_8 = 0x00, /* 64 rand bits, 64 stored bits */
48 VIA_RNG_CHUNK_4 = 0x01, /* 32 rand bits, 32 stored bits */
49 VIA_RNG_CHUNK_4_MASK = 0xFFFFFFFF,
50 VIA_RNG_CHUNK_2 = 0x02, /* 16 rand bits, 32 stored bits */
51 VIA_RNG_CHUNK_2_MASK = 0xFFFF,
52 VIA_RNG_CHUNK_1 = 0x03, /* 8 rand bits, 32 stored bits */
53 VIA_RNG_CHUNK_1_MASK = 0xFF,
57 * Investigate using the 'rep' prefix to obtain 32 bits of random data
58 * in one insn. The upside is potentially better performance. The
59 * downside is that the instruction becomes no longer atomic. Due to
60 * this, just like familiar issues with /dev/random itself, the worst
61 * case of a 'rep xstore' could potentially pause a cpu for an
62 * unreasonably long time. In practice, this condition would likely
63 * only occur when the hardware is failing. (or so we hope :))
65 * Another possible performance boost may come from simply buffering
66 * until we have 4 bytes, thus returning a u32 at a time,
67 * instead of the current u8-at-a-time.
70 static inline u32 xstore(u32 *addr, u32 edx_in)
72 u32 eax_out;
74 asm(".byte 0x0F,0xA7,0xC0 /* xstore %%edi (addr=%0) */"
75 :"=m"(*addr), "=a"(eax_out)
76 :"D"(addr), "d"(edx_in));
78 return eax_out;
81 static int via_rng_data_present(struct hwrng *rng)
83 u32 bytes_out;
84 u32 *via_rng_datum = (u32 *)(&rng->priv);
86 /* We choose the recommended 1-byte-per-instruction RNG rate,
87 * for greater randomness at the expense of speed. Larger
88 * values 2, 4, or 8 bytes-per-instruction yield greater
89 * speed at lesser randomness.
91 * If you change this to another VIA_CHUNK_n, you must also
92 * change the ->n_bytes values in rng_vendor_ops[] tables.
93 * VIA_CHUNK_8 requires further code changes.
95 * A copy of MSR_VIA_RNG is placed in eax_out when xstore
96 * completes.
99 *via_rng_datum = 0; /* paranoia, not really necessary */
100 bytes_out = xstore(via_rng_datum, VIA_RNG_CHUNK_1);
101 bytes_out &= VIA_XSTORE_CNT_MASK;
102 if (bytes_out == 0)
103 return 0;
104 return 1;
107 static int via_rng_data_read(struct hwrng *rng, u32 *data)
109 u32 via_rng_datum = (u32)rng->priv;
111 *data = via_rng_datum;
113 return 1;
116 static int via_rng_init(struct hwrng *rng)
118 u32 lo, hi, old_lo;
120 /* Control the RNG via MSR. Tread lightly and pay very close
121 * close attention to values written, as the reserved fields
122 * are documented to be "undefined and unpredictable"; but it
123 * does not say to write them as zero, so I make a guess that
124 * we restore the values we find in the register.
126 rdmsr(MSR_VIA_RNG, lo, hi);
128 old_lo = lo;
129 lo &= ~(0x7f << VIA_STRFILT_CNT_SHIFT);
130 lo &= ~VIA_XSTORE_CNT_MASK;
131 lo &= ~(VIA_STRFILT_ENABLE | VIA_STRFILT_FAIL | VIA_RAWBITS_ENABLE);
132 lo |= VIA_RNG_ENABLE;
134 if (lo != old_lo)
135 wrmsr(MSR_VIA_RNG, lo, hi);
137 /* perhaps-unnecessary sanity check; remove after testing if
138 unneeded */
139 rdmsr(MSR_VIA_RNG, lo, hi);
140 if ((lo & VIA_RNG_ENABLE) == 0) {
141 printk(KERN_ERR PFX "cannot enable VIA C3 RNG, aborting\n");
142 return -ENODEV;
145 return 0;
149 static struct hwrng via_rng = {
150 .name = "via",
151 .init = via_rng_init,
152 .data_present = via_rng_data_present,
153 .data_read = via_rng_data_read,
157 static int __init mod_init(void)
159 int err;
161 if (!cpu_has_xstore)
162 return -ENODEV;
163 printk(KERN_INFO "VIA RNG detected\n");
164 err = hwrng_register(&via_rng);
165 if (err) {
166 printk(KERN_ERR PFX "RNG registering failed (%d)\n",
167 err);
168 goto out;
170 out:
171 return err;
174 static void __exit mod_exit(void)
176 hwrng_unregister(&via_rng);
179 module_init(mod_init);
180 module_exit(mod_exit);
182 MODULE_DESCRIPTION("H/W RNG driver for VIA chipsets");
183 MODULE_LICENSE("GPL");