1 /*
2  * Copyright 2013, Michael Ellerman, IBM Corporation.
3  *
4  * This program is free software; you can redistribute it and/or
5  * modify it under the terms of the GNU General Public License
6  * as published by the Free Software Foundation; either version
7  * 2 of the License, or (at your option) any later version.
8  */
9 
10 #define pr_fmt(fmt)	"powernv-rng: " fmt
11 
12 #include <linux/kernel.h>
13 #include <linux/of.h>
14 #include <linux/of_address.h>
15 #include <linux/of_platform.h>
16 #include <linux/slab.h>
17 #include <linux/smp.h>
18 #include <asm/archrandom.h>
19 #include <asm/io.h>
20 #include <asm/prom.h>
21 #include <asm/machdep.h>
22 #include <asm/smp.h>
23 
24 
25 struct powernv_rng {
26 	void __iomem *regs;
27 	unsigned long mask;
28 };
29 
30 static DEFINE_PER_CPU(struct powernv_rng *, powernv_rng);
31 
32 
33 static unsigned long rng_whiten(struct powernv_rng *rng, unsigned long val)
34 {
35 	unsigned long parity;
36 
37 	/* Calculate the parity of the value */
38 	asm ("popcntd %0,%1" : "=r" (parity) : "r" (val));
39 
40 	/* xor our value with the previous mask */
41 	val ^= rng->mask;
42 
43 	/* update the mask based on the parity of this value */
44 	rng->mask = (rng->mask << 1) | (parity & 1);
45 
46 	return val;
47 }
48 
49 int powernv_get_random_long(unsigned long *v)
50 {
51 	struct powernv_rng *rng;
52 
53 	rng = get_cpu_var(powernv_rng);
54 
55 	*v = rng_whiten(rng, in_be64(rng->regs));
56 
57 	put_cpu_var(rng);
58 
59 	return 1;
60 }
61 EXPORT_SYMBOL_GPL(powernv_get_random_long);
62 
63 static __init void rng_init_per_cpu(struct powernv_rng *rng,
64 				    struct device_node *dn)
65 {
66 	int chip_id, cpu;
67 
68 	chip_id = of_get_ibm_chip_id(dn);
69 	if (chip_id == -1)
70 		pr_warn("No ibm,chip-id found for %s.\n", dn->full_name);
71 
72 	for_each_possible_cpu(cpu) {
73 		if (per_cpu(powernv_rng, cpu) == NULL ||
74 		    cpu_to_chip_id(cpu) == chip_id) {
75 			per_cpu(powernv_rng, cpu) = rng;
76 		}
77 	}
78 }
79 
80 static __init int rng_create(struct device_node *dn)
81 {
82 	struct powernv_rng *rng;
83 	unsigned long val;
84 
85 	rng = kzalloc(sizeof(*rng), GFP_KERNEL);
86 	if (!rng)
87 		return -ENOMEM;
88 
89 	rng->regs = of_iomap(dn, 0);
90 	if (!rng->regs) {
91 		kfree(rng);
92 		return -ENXIO;
93 	}
94 
95 	val = in_be64(rng->regs);
96 	rng->mask = val;
97 
98 	rng_init_per_cpu(rng, dn);
99 
100 	pr_info_once("Registering arch random hook.\n");
101 
102 	ppc_md.get_random_long = powernv_get_random_long;
103 
104 	return 0;
105 }
106 
107 static __init int rng_init(void)
108 {
109 	struct device_node *dn;
110 	int rc;
111 
112 	for_each_compatible_node(dn, NULL, "ibm,power-rng") {
113 		rc = rng_create(dn);
114 		if (rc) {
115 			pr_err("Failed creating rng for %s (%d).\n",
116 				dn->full_name, rc);
117 			continue;
118 		}
119 
120 		/* Create devices for hwrng driver */
121 		of_platform_device_create(dn, NULL, NULL);
122 	}
123 
124 	return 0;
125 }
126 subsys_initcall(rng_init);
127