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01c9348c76
The hardware RNG on POWER8 and POWER7+ can be relatively slow, since
it can only supply one 64-bit value per microsecond. Currently we
read it in arch_get_random_long(), but that slows down reading from
/dev/urandom since the code in random.c calls arch_get_random_long()
for every longword read from /dev/urandom.
Since the hardware RNG supplies high-quality entropy on every read, it
matches the semantics of arch_get_random_seed_long() better than those
of arch_get_random_long(). Therefore this commit makes the code use
the POWER8/7+ hardware RNG only for arch_get_random_seed_{long,int}
and not for arch_get_random_{long,int}.
This won't affect any other PowerPC-based platforms because none of
them currently support a hardware RNG. To make it clear that the
ppc_md function pointer is used for arch_get_random_seed_*, we rename
it from get_random_long to get_random_seed.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
156 lines
3.0 KiB
C
156 lines
3.0 KiB
C
/*
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* Copyright 2013, Michael Ellerman, IBM Corporation.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#define pr_fmt(fmt) "powernv-rng: " fmt
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#include <linux/kernel.h>
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#include <linux/of.h>
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#include <linux/of_address.h>
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#include <linux/of_platform.h>
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#include <linux/slab.h>
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#include <linux/smp.h>
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#include <asm/archrandom.h>
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#include <asm/io.h>
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#include <asm/prom.h>
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#include <asm/machdep.h>
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#include <asm/smp.h>
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struct powernv_rng {
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void __iomem *regs;
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void __iomem *regs_real;
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unsigned long mask;
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};
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static DEFINE_PER_CPU(struct powernv_rng *, powernv_rng);
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int powernv_hwrng_present(void)
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{
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struct powernv_rng *rng;
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rng = get_cpu_var(powernv_rng);
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put_cpu_var(rng);
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return rng != NULL;
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}
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static unsigned long rng_whiten(struct powernv_rng *rng, unsigned long val)
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{
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unsigned long parity;
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/* Calculate the parity of the value */
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asm ("popcntd %0,%1" : "=r" (parity) : "r" (val));
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/* xor our value with the previous mask */
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val ^= rng->mask;
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/* update the mask based on the parity of this value */
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rng->mask = (rng->mask << 1) | (parity & 1);
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return val;
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}
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int powernv_get_random_real_mode(unsigned long *v)
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{
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struct powernv_rng *rng;
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rng = raw_cpu_read(powernv_rng);
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*v = rng_whiten(rng, in_rm64(rng->regs_real));
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return 1;
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}
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int powernv_get_random_long(unsigned long *v)
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{
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struct powernv_rng *rng;
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rng = get_cpu_var(powernv_rng);
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*v = rng_whiten(rng, in_be64(rng->regs));
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put_cpu_var(rng);
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return 1;
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}
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EXPORT_SYMBOL_GPL(powernv_get_random_long);
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static __init void rng_init_per_cpu(struct powernv_rng *rng,
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struct device_node *dn)
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{
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int chip_id, cpu;
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chip_id = of_get_ibm_chip_id(dn);
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if (chip_id == -1)
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pr_warn("No ibm,chip-id found for %s.\n", dn->full_name);
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for_each_possible_cpu(cpu) {
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if (per_cpu(powernv_rng, cpu) == NULL ||
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cpu_to_chip_id(cpu) == chip_id) {
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per_cpu(powernv_rng, cpu) = rng;
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}
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}
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}
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static __init int rng_create(struct device_node *dn)
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{
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struct powernv_rng *rng;
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struct resource res;
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unsigned long val;
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rng = kzalloc(sizeof(*rng), GFP_KERNEL);
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if (!rng)
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return -ENOMEM;
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if (of_address_to_resource(dn, 0, &res)) {
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kfree(rng);
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return -ENXIO;
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}
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rng->regs_real = (void __iomem *)res.start;
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rng->regs = of_iomap(dn, 0);
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if (!rng->regs) {
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kfree(rng);
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return -ENXIO;
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}
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val = in_be64(rng->regs);
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rng->mask = val;
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rng_init_per_cpu(rng, dn);
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pr_info_once("Registering arch random hook.\n");
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ppc_md.get_random_seed = powernv_get_random_long;
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return 0;
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}
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static __init int rng_init(void)
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{
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struct device_node *dn;
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int rc;
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for_each_compatible_node(dn, NULL, "ibm,power-rng") {
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rc = rng_create(dn);
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if (rc) {
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pr_err("Failed creating rng for %s (%d).\n",
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dn->full_name, rc);
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continue;
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}
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/* Create devices for hwrng driver */
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of_platform_device_create(dn, NULL, NULL);
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}
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return 0;
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}
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machine_subsys_initcall(powernv, rng_init);
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