2 * ST Random Number Generator Driver ST's Platforms
4 * Author: Pankaj Dev: <pankaj.dev@st.com>
5 * Lee Jones <lee.jones@linaro.org>
7 * Copyright (C) 2015 STMicroelectronics (R&D) Limited
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.
14 #include <linux/clk.h>
15 #include <linux/delay.h>
16 #include <linux/hw_random.h>
18 #include <linux/module.h>
20 #include <linux/platform_device.h>
21 #include <linux/slab.h>
24 #define ST_RNG_STATUS_REG 0x20
25 #define ST_RNG_DATA_REG 0x24
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)
32 #define ST_RNG_FIFO_SIZE 8
33 #define ST_RNG_SAMPLE_SIZE 2 /* 2 Byte (16bit) samples */
36 * Samples are documented to be available every 0.667us, so in theory
37 * the 4 sample deep FIFO should take 2.668us to fill. However, during
38 * thorough testing, it became apparent that filling the FIFO actually
39 * takes closer to 12us. We then multiply by 2 in order to account for
40 * the lack of udelay()'s reliability, suggested by Russell King.
42 #define ST_RNG_FILL_FIFO_TIMEOUT (12 * 2)
50 static int st_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
52 struct st_rng_data *ddata = (struct st_rng_data *)rng->priv;
56 if (max < sizeof(u16))
59 /* Wait until FIFO is full - max 4uS*/
60 for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) {
61 status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG);
62 if (status & ST_RNG_STATUS_FIFO_FULL)
67 if (i == ST_RNG_FILL_FIFO_TIMEOUT)
70 for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2)
72 readl_relaxed(ddata->base + ST_RNG_DATA_REG);
74 return i; /* No of bytes read */
77 static int st_rng_probe(struct platform_device *pdev)
79 struct st_rng_data *ddata;
85 ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL);
89 res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
90 base = devm_ioremap_resource(&pdev->dev, res);
94 clk = devm_clk_get(&pdev->dev, NULL);
98 ret = clk_prepare_enable(clk);
102 ddata->ops.priv = (unsigned long)ddata;
103 ddata->ops.read = st_rng_read;
104 ddata->ops.name = pdev->name;
108 dev_set_drvdata(&pdev->dev, ddata);
110 ret = hwrng_register(&ddata->ops);
112 dev_err(&pdev->dev, "Failed to register HW RNG\n");
116 dev_info(&pdev->dev, "Successfully registered HW RNG\n");
121 static int st_rng_remove(struct platform_device *pdev)
123 struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev);
125 hwrng_unregister(&ddata->ops);
127 clk_disable_unprepare(ddata->clk);
132 static const struct of_device_id st_rng_match[] = {
133 { .compatible = "st,rng" },
136 MODULE_DEVICE_TABLE(of, st_rng_match);
138 static struct platform_driver st_rng_driver = {
140 .name = "st-hwrandom",
141 .of_match_table = of_match_ptr(st_rng_match),
143 .probe = st_rng_probe,
144 .remove = st_rng_remove
147 module_platform_driver(st_rng_driver);
149 MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>");
150 MODULE_LICENSE("GPL v2");