1 // SPDX-License-Identifier: GPL-2.0-only
3 * ST Random Number Generator Driver ST's Platforms
5 * Author: Pankaj Dev: <pankaj.dev@st.com>
6 * Lee Jones <lee.jones@linaro.org>
8 * Copyright (C) 2015 STMicroelectronics (R&D) Limited
11 #include <linux/clk.h>
12 #include <linux/delay.h>
13 #include <linux/hw_random.h>
15 #include <linux/module.h>
17 #include <linux/platform_device.h>
18 #include <linux/slab.h>
21 #define ST_RNG_STATUS_REG 0x20
22 #define ST_RNG_DATA_REG 0x24
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)
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)
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.
40 #define ST_RNG_FILL_FIFO_TIMEOUT (12 * 2)
48 static int st_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
50 struct st_rng_data *ddata = (struct st_rng_data *)rng->priv;
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)
62 if (i == ST_RNG_FILL_FIFO_TIMEOUT)
65 for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2)
67 readl_relaxed(ddata->base + ST_RNG_DATA_REG);
69 return i; /* No of bytes read */
72 static int st_rng_probe(struct platform_device *pdev)
74 struct st_rng_data *ddata;
79 ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL);
83 base = devm_platform_ioremap_resource(pdev, 0);
87 clk = devm_clk_get(&pdev->dev, NULL);
91 ret = clk_prepare_enable(clk);
95 ddata->ops.priv = (unsigned long)ddata;
96 ddata->ops.read = st_rng_read;
97 ddata->ops.name = pdev->name;
101 dev_set_drvdata(&pdev->dev, ddata);
103 ret = devm_hwrng_register(&pdev->dev, &ddata->ops);
105 dev_err(&pdev->dev, "Failed to register HW RNG\n");
106 clk_disable_unprepare(clk);
110 dev_info(&pdev->dev, "Successfully registered HW RNG\n");
115 static int st_rng_remove(struct platform_device *pdev)
117 struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev);
119 clk_disable_unprepare(ddata->clk);
124 static const struct of_device_id st_rng_match[] = {
125 { .compatible = "st,rng" },
128 MODULE_DEVICE_TABLE(of, st_rng_match);
130 static struct platform_driver st_rng_driver = {
132 .name = "st-hwrandom",
133 .of_match_table = of_match_ptr(st_rng_match),
135 .probe = st_rng_probe,
136 .remove = st_rng_remove
139 module_platform_driver(st_rng_driver);
141 MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>");
142 MODULE_LICENSE("GPL v2");