1// SPDX-License-Identifier: GPL-2.0-or-later OR MIT
  2/*
  3 * Copyright (c) 2023 David Yang
  4 */
  5
  6#include <linux/err.h>
  7#include <linux/hw_random.h>
  8#include <linux/io.h>
  9#include <linux/iopoll.h>
 10#include <linux/kernel.h>
 11#include <linux/mod_devicetable.h>
 12#include <linux/module.h>
 13#include <linux/platform_device.h>
 14
 15#define RNG_CTRL		0x0
 16#define  RNG_SOURCE			GENMASK(1, 0)
 17#define  DROP_ENABLE			BIT(5)
 18#define  POST_PROCESS_ENABLE		BIT(7)
 19#define  POST_PROCESS_DEPTH		GENMASK(15, 8)
 20#define RNG_NUMBER		0x4
 21#define RNG_STAT		0x8
 22#define  DATA_COUNT			GENMASK(2, 0)	/* max 4 */
 23
 24struct histb_rng_priv {
 25	struct hwrng rng;
 26	void __iomem *base;
 27};
 28
 29/*
 30 * Observed:
 31 * depth = 1 -> ~1ms
 32 * depth = 255 -> ~16ms
 33 */
 34static int histb_rng_wait(void __iomem *base)
 35{
 36	u32 val;
 37
 38	return readl_relaxed_poll_timeout(base + RNG_STAT, val,
 39					  val & DATA_COUNT, 1000, 30 * 1000);
 40}
 41
 42static void histb_rng_init(void __iomem *base, unsigned int depth)
 43{
 44	u32 val;
 45
 46	val = readl_relaxed(base + RNG_CTRL);
 47
 48	val &= ~RNG_SOURCE;
 49	val |= 2;
 50
 51	val &= ~POST_PROCESS_DEPTH;
 52	val |= min(depth, 0xffu) << 8;
 53
 54	val |= POST_PROCESS_ENABLE;
 55	val |= DROP_ENABLE;
 56
 57	writel_relaxed(val, base + RNG_CTRL);
 58}
 59
 60static int histb_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
 61{
 62	struct histb_rng_priv *priv = container_of(rng, typeof(*priv), rng);
 63	void __iomem *base = priv->base;
 64
 65	for (int i = 0; i < max; i += sizeof(u32)) {
 66		if (!(readl_relaxed(base + RNG_STAT) & DATA_COUNT)) {
 67			if (!wait)
 68				return i;
 69			if (histb_rng_wait(base)) {
 70				pr_err("failed to generate random number, generated %d\n",
 71				       i);
 72				return i ? i : -ETIMEDOUT;
 73			}
 74		}
 75		*(u32 *) (data + i) = readl_relaxed(base + RNG_NUMBER);
 76	}
 77
 78	return max;
 79}
 80
 81static unsigned int histb_rng_get_depth(void __iomem *base)
 82{
 83	return (readl_relaxed(base + RNG_CTRL) & POST_PROCESS_DEPTH) >> 8;
 84}
 85
 86static ssize_t
 87depth_show(struct device *dev, struct device_attribute *attr, char *buf)
 88{
 89	struct histb_rng_priv *priv = dev_get_drvdata(dev);
 90	void __iomem *base = priv->base;
 91
 92	return sprintf(buf, "%d\n", histb_rng_get_depth(base));
 93}
 94
 95static ssize_t
 96depth_store(struct device *dev, struct device_attribute *attr,
 97	    const char *buf, size_t count)
 98{
 99	struct histb_rng_priv *priv = dev_get_drvdata(dev);
100	void __iomem *base = priv->base;
101	unsigned int depth;
102
103	if (kstrtouint(buf, 0, &depth))
104		return -ERANGE;
105
106	histb_rng_init(base, depth);
107	return count;
108}
109
110static DEVICE_ATTR_RW(depth);
111
112static struct attribute *histb_rng_attrs[] = {
113	&dev_attr_depth.attr,
114	NULL,
115};
116
117ATTRIBUTE_GROUPS(histb_rng);
118
119static int histb_rng_probe(struct platform_device *pdev)
120{
121	struct device *dev = &pdev->dev;
122	struct histb_rng_priv *priv;
123	void __iomem *base;
124	int ret;
125
126	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
127	if (!priv)
128		return -ENOMEM;
129
130	base = devm_platform_ioremap_resource(pdev, 0);
131	if (IS_ERR(base))
132		return PTR_ERR(base);
133
134	histb_rng_init(base, 144);
135	if (histb_rng_wait(base)) {
136		dev_err(dev, "cannot bring up device\n");
137		return -ENODEV;
138	}
139
140	priv->base = base;
141	priv->rng.name = pdev->name;
142	priv->rng.read = histb_rng_read;
143	ret = devm_hwrng_register(dev, &priv->rng);
144	if (ret) {
145		dev_err(dev, "failed to register hwrng: %d\n", ret);
146		return ret;
147	}
148
149	platform_set_drvdata(pdev, priv);
150	dev_set_drvdata(dev, priv);
151	return 0;
152}
153
154static const struct of_device_id histb_rng_of_match[] = {
155	{ .compatible = "hisilicon,histb-rng", },
156	{ }
157};
158MODULE_DEVICE_TABLE(of, histb_rng_of_match);
159
160static struct platform_driver histb_rng_driver = {
161	.probe = histb_rng_probe,
162	.driver = {
163		.name = "histb-rng",
164		.of_match_table = histb_rng_of_match,
165		.dev_groups = histb_rng_groups,
166	},
167};
168
169module_platform_driver(histb_rng_driver);
170
171MODULE_DESCRIPTION("Hisilicon STB random number generator driver");
172MODULE_LICENSE("Dual MIT/GPL");
173MODULE_AUTHOR("David Yang <mmyangfl@gmail.com>");