1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * Nomadik RNG support
4  *  Copyright 2009 Alessandro Rubini
5  */
6 
7 #include <linux/kernel.h>
8 #include <linux/module.h>
9 #include <linux/device.h>
10 #include <linux/amba/bus.h>
11 #include <linux/hw_random.h>
12 #include <linux/io.h>
13 #include <linux/clk.h>
14 #include <linux/err.h>
15 
16 static struct clk *rng_clk;
17 
18 static int nmk_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
19 {
20 	void __iomem *base = (void __iomem *)rng->priv;
21 
22 	/*
23 	 * The register is 32 bits and gives 16 random bits (low half).
24 	 * A subsequent read will delay the core for 400ns, so we just read
25 	 * once and accept the very unlikely very small delay, even if wait==0.
26 	 */
27 	*(u16 *)data = __raw_readl(base + 8) & 0xffff;
28 	return 2;
29 }
30 
31 /* we have at most one RNG per machine, granted */
32 static struct hwrng nmk_rng = {
33 	.name		= "nomadik",
34 	.read		= nmk_rng_read,
35 };
36 
37 static int nmk_rng_probe(struct amba_device *dev, const struct amba_id *id)
38 {
39 	void __iomem *base;
40 	int ret;
41 
42 	rng_clk = devm_clk_get(&dev->dev, NULL);
43 	if (IS_ERR(rng_clk)) {
44 		dev_err(&dev->dev, "could not get rng clock\n");
45 		ret = PTR_ERR(rng_clk);
46 		return ret;
47 	}
48 
49 	clk_prepare_enable(rng_clk);
50 
51 	ret = amba_request_regions(dev, dev->dev.init_name);
52 	if (ret)
53 		goto out_clk;
54 	ret = -ENOMEM;
55 	base = devm_ioremap(&dev->dev, dev->res.start,
56 			    resource_size(&dev->res));
57 	if (!base)
58 		goto out_release;
59 	nmk_rng.priv = (unsigned long)base;
60 	ret = hwrng_register(&nmk_rng);
61 	if (ret)
62 		goto out_release;
63 	return 0;
64 
65 out_release:
66 	amba_release_regions(dev);
67 out_clk:
68 	clk_disable(rng_clk);
69 	return ret;
70 }
71 
72 static int nmk_rng_remove(struct amba_device *dev)
73 {
74 	hwrng_unregister(&nmk_rng);
75 	amba_release_regions(dev);
76 	clk_disable(rng_clk);
77 	return 0;
78 }
79 
80 static struct amba_id nmk_rng_ids[] = {
81 	{
82 		.id	= 0x000805e1,
83 		.mask	= 0x000fffff, /* top bits are rev and cfg: accept all */
84 	},
85 	{0, 0},
86 };
87 
88 MODULE_DEVICE_TABLE(amba, nmk_rng_ids);
89 
90 static struct amba_driver nmk_rng_driver = {
91 	.drv = {
92 		.owner = THIS_MODULE,
93 		.name = "rng",
94 		},
95 	.probe = nmk_rng_probe,
96 	.remove = nmk_rng_remove,
97 	.id_table = nmk_rng_ids,
98 };
99 
100 module_amba_driver(nmk_rng_driver);
101 
102 MODULE_LICENSE("GPL");
103