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
43struct st_rng_data {
44	void __iomem	*base;
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_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
107static const struct of_device_id st_rng_match[] __maybe_unused = {
108	{ .compatible = "st,rng" },
109	{},
110};
111MODULE_DEVICE_TABLE(of, st_rng_match);
112
113static 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
121module_platform_driver(st_rng_driver);
122
123MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>");
124MODULE_DESCRIPTION("ST Microelectronics HW Random Number Generator");
125MODULE_LICENSE("GPL v2");
126