powerpc: Implement arch_get_random_long/int() for powernv

Add the plumbing to implement arch_get_random_long/int(). It didn't seem
worth adding an extra ppc_md hook for int, so we reuse the one for long.

Add an implementation for powernv based on the hwrng found in power7+
systems. We whiten the output of the hwrng, and the result passes all
the dieharder tests.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/Kconfig

@@ -1012,6 +1012,9 @@ config PHYSICAL_START
 	default "0x00000000"
 endif
 
+config	ARCH_RANDOM
+	def_bool n
+
 source "net/Kconfig"
 
 source "drivers/Kconfig"

arch/powerpc/include/asm/archrandom.h

+#ifndef _ASM_POWERPC_ARCHRANDOM_H
+#define _ASM_POWERPC_ARCHRANDOM_H
+
+#ifdef CONFIG_ARCH_RANDOM
+
+#include <asm/machdep.h>
+
+static inline int arch_get_random_long(unsigned long *v)
+{
+	if (ppc_md.get_random_long)
+		return ppc_md.get_random_long(v);
+
+	return 0;
+}
+
+static inline int arch_get_random_int(unsigned int *v)
+{
+	unsigned long val;
+	int rc;
+
+	rc = arch_get_random_long(&val);
+	if (rc)
+		*v = val;
+
+	return rc;
+}
+
+int powernv_get_random_long(unsigned long *v);
+
+#endif /* CONFIG_ARCH_RANDOM */
+
+#endif /* _ASM_POWERPC_ARCHRANDOM_H */

arch/powerpc/include/asm/machdep.h

@@ -263,6 +263,10 @@ struct machdep_calls {
 	ssize_t (*cpu_probe)(const char *, size_t);
 	ssize_t (*cpu_release)(const char *, size_t);
 #endif
+
+#ifdef CONFIG_ARCH_RANDOM
+	int (*get_random_long)(unsigned long *v);
+#endif
 };
 
 extern void e500_idle(void);

arch/powerpc/platforms/powernv/Kconfig

@@ -9,6 +9,7 @@ config PPC_POWERNV
 	select EPAPR_BOOT
 	select PPC_INDIRECT_PIO
 	select PPC_UDBG_16550
+	select ARCH_RANDOM
 	default y
 
 config POWERNV_MSI

arch/powerpc/platforms/powernv/Makefile

 obj-y			+= setup.o opal-takeover.o opal-wrappers.o opal.o
-obj-y			+= opal-rtc.o opal-nvram.o opal-lpc.o
+obj-y			+= opal-rtc.o opal-nvram.o opal-lpc.o rng.o
 
 obj-$(CONFIG_SMP)	+= smp.o
 obj-$(CONFIG_PCI)	+= pci.o pci-p5ioc2.o pci-ioda.o

arch/powerpc/platforms/powernv/rng.c

+/*
+ * Copyright 2013, Michael Ellerman, IBM Corporation.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#define pr_fmt(fmt)	"powernv-rng: " fmt
+
+#include <linux/kernel.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/slab.h>
+#include <asm/archrandom.h>
+#include <asm/io.h>
+#include <asm/machdep.h>
+
+
+struct powernv_rng {
+	void __iomem *regs;
+	unsigned long mask;
+};
+
+static DEFINE_PER_CPU(struct powernv_rng *, powernv_rng);
+
+
+static unsigned long rng_whiten(struct powernv_rng *rng, unsigned long val)
+{
+	unsigned long parity;
+
+	/* Calculate the parity of the value */
+	asm ("popcntd %0,%1" : "=r" (parity) : "r" (val));
+
+	/* xor our value with the previous mask */
+	val ^= rng->mask;
+
+	/* update the mask based on the parity of this value */
+	rng->mask = (rng->mask << 1) | (parity & 1);
+
+	return val;
+}
+
+int powernv_get_random_long(unsigned long *v)
+{
+	struct powernv_rng *rng;
+
+	rng = get_cpu_var(powernv_rng);
+
+	*v = rng_whiten(rng, in_be64(rng->regs));
+
+	put_cpu_var(rng);
+
+	return 1;
+}
+EXPORT_SYMBOL_GPL(powernv_get_random_long);
+
+static __init void rng_init_per_cpu(struct powernv_rng *rng,
+				    struct device_node *dn)
+{
+	int chip_id, cpu;
+
+	chip_id = of_get_ibm_chip_id(dn);
+	if (chip_id == -1)
+		pr_warn("No ibm,chip-id found for %s.\n", dn->full_name);
+
+	for_each_possible_cpu(cpu) {
+		if (per_cpu(powernv_rng, cpu) == NULL ||
+		    cpu_to_chip_id(cpu) == chip_id) {
+			per_cpu(powernv_rng, cpu) = rng;
+		}
+	}
+}
+
+static __init int rng_create(struct device_node *dn)
+{
+	struct powernv_rng *rng;
+	unsigned long val;
+
+	rng = kzalloc(sizeof(*rng), GFP_KERNEL);
+	if (!rng)
+		return -ENOMEM;
+
+	rng->regs = of_iomap(dn, 0);
+	if (!rng->regs) {
+		kfree(rng);
+		return -ENXIO;
+	}
+
+	val = in_be64(rng->regs);
+	rng->mask = val;
+
+	rng_init_per_cpu(rng, dn);
+
+	pr_info_once("Registering arch random hook.\n");
+
+	ppc_md.get_random_long = powernv_get_random_long;
+
+	return 0;
+}
+
+static __init int rng_init(void)
+{
+	struct device_node *dn;
+	int rc;
+
+	for_each_compatible_node(dn, NULL, "ibm,power-rng") {
+		rc = rng_create(dn);
+		if (rc) {
+			pr_err("Failed creating rng for %s (%d).\n",
+				dn->full_name, rc);
+			continue;
+		}
+
+		/* Create devices for hwrng driver */
+		of_platform_device_create(dn, NULL, NULL);
+	}
+
+	return 0;
+}
+subsys_initcall(rng_init);