1/*
2 * RNG driver for TX4939 Random Number Generators (RNG)
3 *
4 * Copyright (C) 2009 Atsushi Nemoto <anemo@mba.ocn.ne.jp>
5 *
6 * This file is subject to the terms and conditions of the GNU General Public
7 * License.  See the file "COPYING" in the main directory of this archive
8 * for more details.
9 */
10#include <linux/err.h>
11#include <linux/module.h>
12#include <linux/kernel.h>
13#include <linux/init.h>
14#include <linux/delay.h>
15#include <linux/io.h>
16#include <linux/platform_device.h>
17#include <linux/hw_random.h>
18#include <linux/gfp.h>
19
20#define TX4939_RNG_RCSR		0x00000000
21#define TX4939_RNG_ROR(n)	(0x00000018 + (n) * 8)
22
23#define TX4939_RNG_RCSR_INTE	0x00000008
24#define TX4939_RNG_RCSR_RST	0x00000004
25#define TX4939_RNG_RCSR_FIN	0x00000002
26#define TX4939_RNG_RCSR_ST	0x00000001
27
28struct tx4939_rng {
29	struct hwrng rng;
30	void __iomem *base;
31	u64 databuf[3];
32	unsigned int data_avail;
33};
34
35static void rng_io_start(void)
36{
37#ifndef CONFIG_64BIT
38	/*
39	 * readq is reading a 64-bit register using a 64-bit load.  On
40	 * a 32-bit kernel however interrupts or any other processor
41	 * exception would clobber the upper 32-bit of the processor
42	 * register so interrupts need to be disabled.
43	 */
44	local_irq_disable();
45#endif
46}
47
48static void rng_io_end(void)
49{
50#ifndef CONFIG_64BIT
51	local_irq_enable();
52#endif
53}
54
55static u64 read_rng(void __iomem *base, unsigned int offset)
56{
57	return ____raw_readq(base + offset);
58}
59
60static void write_rng(u64 val, void __iomem *base, unsigned int offset)
61{
62	return ____raw_writeq(val, base + offset);
63}
64
65static int tx4939_rng_data_present(struct hwrng *rng, int wait)
66{
67	struct tx4939_rng *rngdev = container_of(rng, struct tx4939_rng, rng);
68	int i;
69
70	if (rngdev->data_avail)
71		return rngdev->data_avail;
72	for (i = 0; i < 20; i++) {
73		rng_io_start();
74		if (!(read_rng(rngdev->base, TX4939_RNG_RCSR)
75		      & TX4939_RNG_RCSR_ST)) {
76			rngdev->databuf[0] =
77				read_rng(rngdev->base, TX4939_RNG_ROR(0));
78			rngdev->databuf[1] =
79				read_rng(rngdev->base, TX4939_RNG_ROR(1));
80			rngdev->databuf[2] =
81				read_rng(rngdev->base, TX4939_RNG_ROR(2));
82			rngdev->data_avail =
83				sizeof(rngdev->databuf) / sizeof(u32);
84			/* Start RNG */
85			write_rng(TX4939_RNG_RCSR_ST,
86				  rngdev->base, TX4939_RNG_RCSR);
87			wait = 0;
88		}
89		rng_io_end();
90		if (!wait)
91			break;
92		/* 90 bus clock cycles by default for generation */
93		ndelay(90 * 5);
94	}
95	return rngdev->data_avail;
96}
97
98static int tx4939_rng_data_read(struct hwrng *rng, u32 *buffer)
99{
100	struct tx4939_rng *rngdev = container_of(rng, struct tx4939_rng, rng);
101
102	rngdev->data_avail--;
103	*buffer = *((u32 *)&rngdev->databuf + rngdev->data_avail);
104	return sizeof(u32);
105}
106
107static int __init tx4939_rng_probe(struct platform_device *dev)
108{
109	struct tx4939_rng *rngdev;
110	int i;
111
112	rngdev = devm_kzalloc(&dev->dev, sizeof(*rngdev), GFP_KERNEL);
113	if (!rngdev)
114		return -ENOMEM;
115	rngdev->base = devm_platform_ioremap_resource(dev, 0);
116	if (IS_ERR(rngdev->base))
117		return PTR_ERR(rngdev->base);
118
119	rngdev->rng.name = dev_name(&dev->dev);
120	rngdev->rng.data_present = tx4939_rng_data_present;
121	rngdev->rng.data_read = tx4939_rng_data_read;
122
123	rng_io_start();
124	/* Reset RNG */
125	write_rng(TX4939_RNG_RCSR_RST, rngdev->base, TX4939_RNG_RCSR);
126	write_rng(0, rngdev->base, TX4939_RNG_RCSR);
127	/* Start RNG */
128	write_rng(TX4939_RNG_RCSR_ST, rngdev->base, TX4939_RNG_RCSR);
129	rng_io_end();
130	/*
131	 * Drop first two results.  From the datasheet:
132	 * The quality of the random numbers generated immediately
133	 * after reset can be insufficient.  Therefore, do not use
134	 * random numbers obtained from the first and second
135	 * generations; use the ones from the third or subsequent
136	 * generation.
137	 */
138	for (i = 0; i < 2; i++) {
139		rngdev->data_avail = 0;
140		if (!tx4939_rng_data_present(&rngdev->rng, 1))
141			return -EIO;
142	}
143
144	platform_set_drvdata(dev, rngdev);
145	return devm_hwrng_register(&dev->dev, &rngdev->rng);
146}
147
148static struct platform_driver tx4939_rng_driver = {
149	.driver		= {
150		.name	= "tx4939-rng",
151	},
152};
153
154module_platform_driver_probe(tx4939_rng_driver, tx4939_rng_probe);
155
156MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver for TX4939");
157MODULE_LICENSE("GPL");
158