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
 45struct st_rng_data {
 46	void __iomem	*base;
 47	struct clk	*clk;
 48	struct hwrng	ops;
 49};
 50
 51static 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	if (max < sizeof(u16))
 58		return -EINVAL;
 59
 60	/* Wait until FIFO is full - max 4uS*/
 61	for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) {
 62		status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG);
 63		if (status & ST_RNG_STATUS_FIFO_FULL)
 64			break;
 65		udelay(1);
 66	}
 67
 68	if (i == ST_RNG_FILL_FIFO_TIMEOUT)
 69		return 0;
 70
 71	for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2)
 72		*(u16 *)(data + i) =
 73			readl_relaxed(ddata->base + ST_RNG_DATA_REG);
 74
 75	return i;	/* No of bytes read */
 76}
 77
 78static int st_rng_probe(struct platform_device *pdev)
 79{
 80	struct st_rng_data *ddata;
 81	struct resource *res;
 82	struct clk *clk;
 83	void __iomem *base;
 84	int ret;
 85
 86	ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL);
 87	if (!ddata)
 88		return -ENOMEM;
 89
 90	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 91	base = devm_ioremap_resource(&pdev->dev, res);
 92	if (IS_ERR(base))
 93		return PTR_ERR(base);
 94
 95	clk = devm_clk_get(&pdev->dev, NULL);
 96	if (IS_ERR(clk))
 97		return PTR_ERR(clk);
 98
 99	ret = clk_prepare_enable(clk);
100	if (ret)
101		return ret;
102
103	ddata->ops.priv	= (unsigned long)ddata;
104	ddata->ops.read	= st_rng_read;
105	ddata->ops.name	= pdev->name;
106	ddata->base	= base;
107	ddata->clk	= clk;
108
109	dev_set_drvdata(&pdev->dev, ddata);
110
111	ret = hwrng_register(&ddata->ops);
112	if (ret) {
113		dev_err(&pdev->dev, "Failed to register HW RNG\n");
114		return ret;
115	}
116
117	dev_info(&pdev->dev, "Successfully registered HW RNG\n");
118
119	return 0;
120}
121
122static int st_rng_remove(struct platform_device *pdev)
123{
124	struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev);
125
126	hwrng_unregister(&ddata->ops);
127
128	clk_disable_unprepare(ddata->clk);
129
130	return 0;
131}
132
133static const struct of_device_id st_rng_match[] = {
134	{ .compatible = "st,rng" },
135	{},
136};
137MODULE_DEVICE_TABLE(of, st_rng_match);
138
139static struct platform_driver st_rng_driver = {
140	.driver = {
141		.name = "st-hwrandom",
142		.of_match_table = of_match_ptr(st_rng_match),
143	},
144	.probe = st_rng_probe,
145	.remove = st_rng_remove
146};
147
148module_platform_driver(st_rng_driver);
149
150MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>");
151MODULE_LICENSE("GPL v2");