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 
28 struct 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 
40 static 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 
49 static 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 
70 static 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 
77 static 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 
102 static const struct of_device_id pic32_rng_of_match[] __maybe_unused = {
103 	{ .compatible	= "microchip,pic32mzda-rng", },
104 	{ /* sentinel */ }
105 };
106 MODULE_DEVICE_TABLE(of, pic32_rng_of_match);
107 
108 static 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 
116 module_platform_driver(pic32_rng_driver);
117 
118 MODULE_LICENSE("GPL");
119 MODULE_AUTHOR("Joshua Henderson <joshua.henderson@microchip.com>");
120 MODULE_DESCRIPTION("Microchip PIC32 RNG Driver");
121