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15#include <linux/bits.h>
16#include <linux/device.h>
17#include <linux/hw_random.h>
18#include <linux/module.h>
19#include <linux/platform_device.h>
20#include <linux/arm-smccc.h>
21
22#ifdef CONFIG_ARM64
23#define ARM_SMCCC_TRNG_RND ARM_SMCCC_TRNG_RND64
24#define MAX_BITS_PER_CALL (3 * 64UL)
25#else
26#define ARM_SMCCC_TRNG_RND ARM_SMCCC_TRNG_RND32
27#define MAX_BITS_PER_CALL (3 * 32UL)
28#endif
29
30
31#define SMCCC_TRNG_MAX_TRIES 20
32
33#define SMCCC_RET_TRNG_INVALID_PARAMETER -2
34#define SMCCC_RET_TRNG_NO_ENTROPY -3
35
36static int copy_from_registers(char *buf, struct arm_smccc_res *res,
37 size_t bytes)
38{
39 unsigned int chunk, copied;
40
41 if (bytes == 0)
42 return 0;
43
44 chunk = min(bytes, sizeof(long));
45 memcpy(buf, &res->a3, chunk);
46 copied = chunk;
47 if (copied >= bytes)
48 return copied;
49
50 chunk = min((bytes - copied), sizeof(long));
51 memcpy(&buf[copied], &res->a2, chunk);
52 copied += chunk;
53 if (copied >= bytes)
54 return copied;
55
56 chunk = min((bytes - copied), sizeof(long));
57 memcpy(&buf[copied], &res->a1, chunk);
58
59 return copied + chunk;
60}
61
62static int smccc_trng_read(struct hwrng *rng, void *data, size_t max, bool wait)
63{
64 struct arm_smccc_res res;
65 u8 *buf = data;
66 unsigned int copied = 0;
67 int tries = 0;
68
69 while (copied < max) {
70 size_t bits = min_t(size_t, (max - copied) * BITS_PER_BYTE,
71 MAX_BITS_PER_CALL);
72
73 arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND, bits, &res);
74 if ((int)res.a0 < 0)
75 return (int)res.a0;
76
77 switch ((int)res.a0) {
78 case SMCCC_RET_SUCCESS:
79 copied += copy_from_registers(buf + copied, &res,
80 bits / BITS_PER_BYTE);
81 tries = 0;
82 break;
83 case SMCCC_RET_TRNG_NO_ENTROPY:
84 if (!wait)
85 return copied;
86 tries++;
87 if (tries >= SMCCC_TRNG_MAX_TRIES)
88 return copied;
89 cond_resched();
90 break;
91 }
92 }
93
94 return copied;
95}
96
97static int smccc_trng_probe(struct platform_device *pdev)
98{
99 struct hwrng *trng;
100
101 trng = devm_kzalloc(&pdev->dev, sizeof(*trng), GFP_KERNEL);
102 if (!trng)
103 return -ENOMEM;
104
105 trng->name = "smccc_trng";
106 trng->read = smccc_trng_read;
107
108 platform_set_drvdata(pdev, trng);
109
110 return devm_hwrng_register(&pdev->dev, trng);
111}
112
113static struct platform_driver smccc_trng_driver = {
114 .driver = {
115 .name = "smccc_trng",
116 },
117 .probe = smccc_trng_probe,
118};
119module_platform_driver(smccc_trng_driver);
120
121MODULE_ALIAS("platform:smccc_trng");
122MODULE_AUTHOR("Andre Przywara");
123MODULE_LICENSE("GPL");
124