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 clk	*clk;
 46	struct hwrng	ops;
 47};
 48
 49static int st_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
 50{
 51	struct st_rng_data *ddata = (struct st_rng_data *)rng->priv;
 52	u32 status;
 53	int i;
 54
 55	/* Wait until FIFO is full - max 4uS*/
 56	for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) {
 57		status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG);
 58		if (status & ST_RNG_STATUS_FIFO_FULL)
 59			break;
 60		udelay(1);
 61	}
 62
 63	if (i == ST_RNG_FILL_FIFO_TIMEOUT)
 64		return 0;
 65
 66	for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2)
 67		*(u16 *)(data + i) =
 68			readl_relaxed(ddata->base + ST_RNG_DATA_REG);
 69
 70	return i;	/* No of bytes read */
 71}
 72
 73static int st_rng_probe(struct platform_device *pdev)
 74{
 75	struct st_rng_data *ddata;
 76	struct clk *clk;
 77	void __iomem *base;
 78	int ret;
 79
 80	ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL);
 81	if (!ddata)
 82		return -ENOMEM;
 83
 84	base = devm_platform_ioremap_resource(pdev, 0);
 85	if (IS_ERR(base))
 86		return PTR_ERR(base);
 87
 88	clk = devm_clk_get(&pdev->dev, NULL);
 89	if (IS_ERR(clk))
 90		return PTR_ERR(clk);
 91
 92	ret = clk_prepare_enable(clk);
 93	if (ret)
 94		return ret;
 95
 96	ddata->ops.priv	= (unsigned long)ddata;
 97	ddata->ops.read	= st_rng_read;
 98	ddata->ops.name	= pdev->name;
 99	ddata->base	= base;
100	ddata->clk	= clk;
101
102	dev_set_drvdata(&pdev->dev, ddata);
103
104	ret = devm_hwrng_register(&pdev->dev, &ddata->ops);
105	if (ret) {
106		dev_err(&pdev->dev, "Failed to register HW RNG\n");
107		clk_disable_unprepare(clk);
108		return ret;
109	}
110
111	dev_info(&pdev->dev, "Successfully registered HW RNG\n");
112
113	return 0;
114}
115
116static int st_rng_remove(struct platform_device *pdev)
117{
118	struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev);
119
120	clk_disable_unprepare(ddata->clk);
121
122	return 0;
123}
124
125static const struct of_device_id st_rng_match[] __maybe_unused = {
126	{ .compatible = "st,rng" },
127	{},
128};
129MODULE_DEVICE_TABLE(of, st_rng_match);
130
131static struct platform_driver st_rng_driver = {
132	.driver = {
133		.name = "st-hwrandom",
134		.of_match_table = of_match_ptr(st_rng_match),
135	},
136	.probe = st_rng_probe,
137	.remove = st_rng_remove
138};
139
140module_platform_driver(st_rng_driver);
141
142MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>");
143MODULE_LICENSE("GPL v2");