1 /*
2 * ST Random Number Generator Driver ST's Platforms
3 *
4 * Author: Pankaj Dev: <pankaj.dev@st.com>
5 * Lee Jones <lee.jones@linaro.org>
6 *
7 * Copyright (C) 2015 STMicroelectronics (R&D) Limited
8 *
9 * This program is free software; you can redistribute it and/or modify
10 * it under the terms of the GNU General Public License version 2 as
11 * published by the Free Software Foundation.
12 */
13
14 #include <linux/clk.h>
15 #include <linux/delay.h>
16 #include <linux/hw_random.h>
17 #include <linux/io.h>
18 #include <linux/module.h>
19 #include <linux/of.h>
20 #include <linux/platform_device.h>
21 #include <linux/slab.h>
22
23 /* Registers */
24 #define ST_RNG_STATUS_REG 0x20
25 #define ST_RNG_DATA_REG 0x24
26
27 /* Registers fields */
28 #define ST_RNG_STATUS_BAD_SEQUENCE BIT(0)
29 #define ST_RNG_STATUS_BAD_ALTERNANCE BIT(1)
30 #define ST_RNG_STATUS_FIFO_FULL BIT(5)
31
32 #define ST_RNG_SAMPLE_SIZE 2 /* 2 Byte (16bit) samples */
33 #define ST_RNG_FIFO_DEPTH 4
34 #define ST_RNG_FIFO_SIZE (ST_RNG_FIFO_DEPTH * ST_RNG_SAMPLE_SIZE)
35
36 /*
37 * Samples are documented to be available every 0.667us, so in theory
38 * the 4 sample deep FIFO should take 2.668us to fill. However, during
39 * thorough testing, it became apparent that filling the FIFO actually
40 * takes closer to 12us. We then multiply by 2 in order to account for
41 * the lack of udelay()'s reliability, suggested by Russell King.
42 */
43 #define ST_RNG_FILL_FIFO_TIMEOUT (12 * 2)
44
45 struct st_rng_data {
46 void __iomem *base;
47 struct clk *clk;
48 struct hwrng ops;
49 };
50
st_rng_read(struct hwrng * rng,void * data,size_t max,bool wait)51 static int st_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
52 {
53 struct st_rng_data *ddata = (struct st_rng_data *)rng->priv;
54 u32 status;
55 int i;
56
57 /* Wait until FIFO is full - max 4uS*/
58 for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) {
59 status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG);
60 if (status & ST_RNG_STATUS_FIFO_FULL)
61 break;
62 udelay(1);
63 }
64
65 if (i == ST_RNG_FILL_FIFO_TIMEOUT)
66 return 0;
67
68 for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2)
69 *(u16 *)(data + i) =
70 readl_relaxed(ddata->base + ST_RNG_DATA_REG);
71
72 return i; /* No of bytes read */
73 }
74
st_rng_probe(struct platform_device * pdev)75 static int st_rng_probe(struct platform_device *pdev)
76 {
77 struct st_rng_data *ddata;
78 struct resource *res;
79 struct clk *clk;
80 void __iomem *base;
81 int ret;
82
83 ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL);
84 if (!ddata)
85 return -ENOMEM;
86
87 res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
88 base = devm_ioremap_resource(&pdev->dev, res);
89 if (IS_ERR(base))
90 return PTR_ERR(base);
91
92 clk = devm_clk_get(&pdev->dev, NULL);
93 if (IS_ERR(clk))
94 return PTR_ERR(clk);
95
96 ret = clk_prepare_enable(clk);
97 if (ret)
98 return ret;
99
100 ddata->ops.priv = (unsigned long)ddata;
101 ddata->ops.read = st_rng_read;
102 ddata->ops.name = pdev->name;
103 ddata->base = base;
104 ddata->clk = clk;
105
106 dev_set_drvdata(&pdev->dev, ddata);
107
108 ret = hwrng_register(&ddata->ops);
109 if (ret) {
110 dev_err(&pdev->dev, "Failed to register HW RNG\n");
111 clk_disable_unprepare(clk);
112 return ret;
113 }
114
115 dev_info(&pdev->dev, "Successfully registered HW RNG\n");
116
117 return 0;
118 }
119
st_rng_remove(struct platform_device * pdev)120 static int st_rng_remove(struct platform_device *pdev)
121 {
122 struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev);
123
124 hwrng_unregister(&ddata->ops);
125
126 clk_disable_unprepare(ddata->clk);
127
128 return 0;
129 }
130
131 static const struct of_device_id st_rng_match[] = {
132 { .compatible = "st,rng" },
133 {},
134 };
135 MODULE_DEVICE_TABLE(of, st_rng_match);
136
137 static struct platform_driver st_rng_driver = {
138 .driver = {
139 .name = "st-hwrandom",
140 .of_match_table = of_match_ptr(st_rng_match),
141 },
142 .probe = st_rng_probe,
143 .remove = st_rng_remove
144 };
145
146 module_platform_driver(st_rng_driver);
147
148 MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>");
149 MODULE_LICENSE("GPL v2");
150
