1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * ST Random Number Generator Driver ST's Platforms
4 *
5 * Author: Pankaj Dev: <pankaj.dev@st.com>
6 * Lee Jones <lee.jones@linaro.org>
7 *
8 * Copyright (C) 2015 STMicroelectronics (R&D) Limited
9 */
10
11 #include <linux/clk.h>
12 #include <linux/delay.h>
13 #include <linux/hw_random.h>
14 #include <linux/io.h>
15 #include <linux/kernel.h>
16 #include <linux/module.h>
17 #include <linux/of.h>
18 #include <linux/platform_device.h>
19 #include <linux/slab.h>
20
21 /* Registers */
22 #define ST_RNG_STATUS_REG 0x20
23 #define ST_RNG_DATA_REG 0x24
24
25 /* Registers fields */
26 #define ST_RNG_STATUS_BAD_SEQUENCE BIT(0)
27 #define ST_RNG_STATUS_BAD_ALTERNANCE BIT(1)
28 #define ST_RNG_STATUS_FIFO_FULL BIT(5)
29
30 #define ST_RNG_SAMPLE_SIZE 2 /* 2 Byte (16bit) samples */
31 #define ST_RNG_FIFO_DEPTH 4
32 #define ST_RNG_FIFO_SIZE (ST_RNG_FIFO_DEPTH * ST_RNG_SAMPLE_SIZE)
33
34 /*
35 * Samples are documented to be available every 0.667us, so in theory
36 * the 4 sample deep FIFO should take 2.668us to fill. However, during
37 * thorough testing, it became apparent that filling the FIFO actually
38 * takes closer to 12us. We then multiply by 2 in order to account for
39 * the lack of udelay()'s reliability, suggested by Russell King.
40 */
41 #define ST_RNG_FILL_FIFO_TIMEOUT (12 * 2)
42
43 struct st_rng_data {
44 void __iomem *base;
45 struct hwrng ops;
46 };
47
st_rng_read(struct hwrng * rng,void * data,size_t max,bool wait)48 static int st_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
49 {
50 struct st_rng_data *ddata = (struct st_rng_data *)rng->priv;
51 u32 status;
52 int i;
53
54 /* Wait until FIFO is full - max 4uS*/
55 for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) {
56 status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG);
57 if (status & ST_RNG_STATUS_FIFO_FULL)
58 break;
59 udelay(1);
60 }
61
62 if (i == ST_RNG_FILL_FIFO_TIMEOUT)
63 return 0;
64
65 for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2)
66 *(u16 *)(data + i) =
67 readl_relaxed(ddata->base + ST_RNG_DATA_REG);
68
69 return i; /* No of bytes read */
70 }
71
st_rng_probe(struct platform_device * pdev)72 static int st_rng_probe(struct platform_device *pdev)
73 {
74 struct st_rng_data *ddata;
75 struct clk *clk;
76 void __iomem *base;
77 int ret;
78
79 ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL);
80 if (!ddata)
81 return -ENOMEM;
82
83 base = devm_platform_ioremap_resource(pdev, 0);
84 if (IS_ERR(base))
85 return PTR_ERR(base);
86
87 clk = devm_clk_get_enabled(&pdev->dev, NULL);
88 if (IS_ERR(clk))
89 return PTR_ERR(clk);
90
91 ddata->ops.priv = (unsigned long)ddata;
92 ddata->ops.read = st_rng_read;
93 ddata->ops.name = pdev->name;
94 ddata->base = base;
95
96 ret = devm_hwrng_register(&pdev->dev, &ddata->ops);
97 if (ret) {
98 dev_err(&pdev->dev, "Failed to register HW RNG\n");
99 return ret;
100 }
101
102 dev_info(&pdev->dev, "Successfully registered HW RNG\n");
103
104 return 0;
105 }
106
107 static const struct of_device_id st_rng_match[] __maybe_unused = {
108 { .compatible = "st,rng" },
109 {},
110 };
111 MODULE_DEVICE_TABLE(of, st_rng_match);
112
113 static struct platform_driver st_rng_driver = {
114 .driver = {
115 .name = "st-hwrandom",
116 .of_match_table = of_match_ptr(st_rng_match),
117 },
118 .probe = st_rng_probe,
119 };
120
121 module_platform_driver(st_rng_driver);
122
123 MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>");
124 MODULE_DESCRIPTION("ST Microelectronics HW Random Number Generator");
125 MODULE_LICENSE("GPL v2");
126