[PATCH] Add VIA HW RNG driver

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
index defe68736959bdcf72a64bfe8dadab8e05b93a57..01e2691d568cac6084268796481b9981dd41ccd3 100644 (file)
--- a/drivers/char/hw_random/Kconfig
+++ b/drivers/char/hw_random/Kconfig
@@ -48,3 +48,16 @@ config HW_RANDOM_GEODE
          module will be called geode-rng.
 
          If unsure, say Y.
+
+config HW_RANDOM_VIA
+       tristate "VIA HW Random Number Generator support"
+       depends on HW_RANDOM && X86_32
+       default y
+       ---help---
+         This driver provides kernel-side support for the Random Number
+         Generator hardware found on VIA based motherboards.
+
+         To compile this driver as a module, choose M here: the
+         module will be called via-rng.
+
+         If unsure, say Y.

diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
index 19ff20e5fb1b950b31bbac509578e3e6ded7de45..f03bdf23f7bc904ef71fbe9d78802d0e16b96f8e 100644 (file)
--- a/drivers/char/hw_random/Makefile
+++ b/drivers/char/hw_random/Makefile
@@ -6,3 +6,4 @@ obj-$(CONFIG_HW_RANDOM) += core.o
 obj-$(CONFIG_HW_RANDOM_INTEL) += intel-rng.o
 obj-$(CONFIG_HW_RANDOM_AMD) += amd-rng.o
 obj-$(CONFIG_HW_RANDOM_GEODE) += geode-rng.o
+obj-$(CONFIG_HW_RANDOM_VIA) += via-rng.o

diff --git a/drivers/char/hw_random/via-rng.c b/drivers/char/hw_random/via-rng.c
new file mode 100644 (file)
index 0000000..0e786b6
--- /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");