tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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/module.h>
16#include <linux/of.h>
17#include <linux/platform_device.h>
18#include <linux/slab.h>
19
20/* Registers */
21#define ST_RNG_STATUS_REG 0x20
22#define ST_RNG_DATA_REG 0x24
23
24/* Registers fields */
25#define ST_RNG_STATUS_BAD_SEQUENCE BIT(0)
26#define ST_RNG_STATUS_BAD_ALTERNANCE BIT(1)
27#define ST_RNG_STATUS_FIFO_FULL BIT(5)
28
29#define ST_RNG_SAMPLE_SIZE 2 /* 2 Byte (16bit) samples */
30#define ST_RNG_FIFO_DEPTH 4
31#define ST_RNG_FIFO_SIZE (ST_RNG_FIFO_DEPTH * ST_RNG_SAMPLE_SIZE)
32
33/*
34 * Samples are documented to be available every 0.667us, so in theory
35 * the 4 sample deep FIFO should take 2.668us to fill. However, during
36 * thorough testing, it became apparent that filling the FIFO actually
37 * takes closer to 12us. We then multiply by 2 in order to account for
38 * the lack of udelay()'s reliability, suggested by Russell King.
39 */
40#define ST_RNG_FILL_FIFO_TIMEOUT (12 * 2)
41
42struct st_rng_data {
43 void __iomem *base;
44 struct clk *clk;
45 struct hwrng ops;
46};
47
48static 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
72static 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(&pdev->dev, NULL);
88 if (IS_ERR(clk))
89 return PTR_ERR(clk);
90
91 ret = clk_prepare_enable(clk);
92 if (ret)
93 return ret;
94
95 ddata->ops.priv = (unsigned long)ddata;
96 ddata->ops.read = st_rng_read;
97 ddata->ops.name = pdev->name;
98 ddata->base = base;
99 ddata->clk = clk;
100
101 dev_set_drvdata(&pdev->dev, ddata);
102
103 ret = devm_hwrng_register(&pdev->dev, &ddata->ops);
104 if (ret) {
105 dev_err(&pdev->dev, "Failed to register HW RNG\n");
106 clk_disable_unprepare(clk);
107 return ret;
108 }
109
110 dev_info(&pdev->dev, "Successfully registered HW RNG\n");
111
112 return 0;
113}
114
115static int st_rng_remove(struct platform_device *pdev)
116{
117 struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev);
118
119 clk_disable_unprepare(ddata->clk);
120
121 return 0;
122}
123
124static const struct of_device_id st_rng_match[] = {
125 { .compatible = "st,rng" },
126 {},
127};
128MODULE_DEVICE_TABLE(of, st_rng_match);
129
130static struct platform_driver st_rng_driver = {
131 .driver = {
132 .name = "st-hwrandom",
133 .of_match_table = of_match_ptr(st_rng_match),
134 },
135 .probe = st_rng_probe,
136 .remove = st_rng_remove
137};
138
139module_platform_driver(st_rng_driver);
140
141MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>");
142MODULE_LICENSE("GPL v2");