1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * PIC32 RNG driver
4 *
5 * Joshua Henderson <joshua.henderson@microchip.com>
6 * Copyright (C) 2016 Microchip Technology Inc.  All rights reserved.
7 */
8
9#include <linux/clk.h>
10#include <linux/clkdev.h>
11#include <linux/err.h>
12#include <linux/hw_random.h>
13#include <linux/io.h>
14#include <linux/kernel.h>
15#include <linux/mod_devicetable.h>
16#include <linux/module.h>
17#include <linux/platform_device.h>
18#include <linux/slab.h>
19
20#define RNGCON		0x04
21#define TRNGEN		BIT(8)
22#define TRNGMOD		BIT(11)
23#define RNGSEED1	0x18
24#define RNGSEED2	0x1C
25#define RNGRCNT		0x20
26#define RCNT_MASK	0x7F
27
28struct pic32_rng {
29	void __iomem	*base;
30	struct hwrng	rng;
31};
32
33/*
34 * The TRNG can generate up to 24Mbps. This is a timeout that should be safe
35 * enough given the instructions in the loop and that the TRNG may not always
36 * be at maximum rate.
37 */
38#define RNG_TIMEOUT 500
39
40static int pic32_rng_init(struct hwrng *rng)
41{
42	struct pic32_rng *priv = container_of(rng, struct pic32_rng, rng);
43
44	/* enable TRNG in enhanced mode */
45	writel(TRNGEN | TRNGMOD, priv->base + RNGCON);
46	return 0;
47}
48
49static int pic32_rng_read(struct hwrng *rng, void *buf, size_t max,
50			  bool wait)
51{
52	struct pic32_rng *priv = container_of(rng, struct pic32_rng, rng);
53	u64 *data = buf;
54	u32 t;
55	unsigned int timeout = RNG_TIMEOUT;
56
57	do {
58		t = readl(priv->base + RNGRCNT) & RCNT_MASK;
59		if (t == 64) {
60			/* TRNG value comes through the seed registers */
61			*data = ((u64)readl(priv->base + RNGSEED2) << 32) +
62				readl(priv->base + RNGSEED1);
63			return 8;
64		}
65	} while (wait && --timeout);
66
67	return -EIO;
68}
69
70static void pic32_rng_cleanup(struct hwrng *rng)
71{
72	struct pic32_rng *priv = container_of(rng, struct pic32_rng, rng);
73
74	writel(0, priv->base + RNGCON);
75}
76
77static int pic32_rng_probe(struct platform_device *pdev)
78{
79	struct pic32_rng *priv;
80	struct clk *clk;
81
82	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
83	if (!priv)
84		return -ENOMEM;
85
86	priv->base = devm_platform_ioremap_resource(pdev, 0);
87	if (IS_ERR(priv->base))
88		return PTR_ERR(priv->base);
89
90	clk = devm_clk_get_enabled(&pdev->dev, NULL);
91	if (IS_ERR(clk))
92		return PTR_ERR(clk);
93
94	priv->rng.name = pdev->name;
95	priv->rng.init = pic32_rng_init;
96	priv->rng.read = pic32_rng_read;
97	priv->rng.cleanup = pic32_rng_cleanup;
98
99	return devm_hwrng_register(&pdev->dev, &priv->rng);
100}
101
102static const struct of_device_id pic32_rng_of_match[] __maybe_unused = {
103	{ .compatible	= "microchip,pic32mzda-rng", },
104	{ /* sentinel */ }
105};
106MODULE_DEVICE_TABLE(of, pic32_rng_of_match);
107
108static struct platform_driver pic32_rng_driver = {
109	.probe		= pic32_rng_probe,
110	.driver		= {
111		.name	= "pic32-rng",
112		.of_match_table = pic32_rng_of_match,
113	},
114};
115
116module_platform_driver(pic32_rng_driver);
117
118MODULE_LICENSE("GPL");
119MODULE_AUTHOR("Joshua Henderson <joshua.henderson@microchip.com>");
120MODULE_DESCRIPTION("Microchip PIC32 RNG Driver");
121