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/module.h>
 11#include <linux/kernel.h>
 12#include <linux/init.h>
 13#include <linux/delay.h>
 14#include <linux/io.h>
 15#include <linux/platform_device.h>
 16#include <linux/hw_random.h>
 17#include <linux/gfp.h>
 18
 19#define TX4939_RNG_RCSR		0x00000000
 20#define TX4939_RNG_ROR(n)	(0x00000018 + (n) * 8)
 21
 22#define TX4939_RNG_RCSR_INTE	0x00000008
 23#define TX4939_RNG_RCSR_RST	0x00000004
 24#define TX4939_RNG_RCSR_FIN	0x00000002
 25#define TX4939_RNG_RCSR_ST	0x00000001
 26
 27struct tx4939_rng {
 28	struct hwrng rng;
 29	void __iomem *base;
 30	u64 databuf[3];
 31	unsigned int data_avail;
 32};
 33
 34static void rng_io_start(void)
 35{
 36#ifndef CONFIG_64BIT
 37	/*
 38	 * readq is reading a 64-bit register using a 64-bit load.  On
 39	 * a 32-bit kernel however interrupts or any other processor
 40	 * exception would clobber the upper 32-bit of the processor
 41	 * register so interrupts need to be disabled.
 42	 */
 43	local_irq_disable();
 44#endif
 45}
 46
 47static void rng_io_end(void)
 48{
 49#ifndef CONFIG_64BIT
 50	local_irq_enable();
 51#endif
 52}
 53
 54static u64 read_rng(void __iomem *base, unsigned int offset)
 55{
 56	return ____raw_readq(base + offset);
 57}
 58
 59static void write_rng(u64 val, void __iomem *base, unsigned int offset)
 60{
 61	return ____raw_writeq(val, base + offset);
 62}
 63
 64static int tx4939_rng_data_present(struct hwrng *rng, int wait)
 65{
 66	struct tx4939_rng *rngdev = container_of(rng, struct tx4939_rng, rng);
 67	int i;
 68
 69	if (rngdev->data_avail)
 70		return rngdev->data_avail;
 71	for (i = 0; i < 20; i++) {
 72		rng_io_start();
 73		if (!(read_rng(rngdev->base, TX4939_RNG_RCSR)
 74		      & TX4939_RNG_RCSR_ST)) {
 75			rngdev->databuf[0] =
 76				read_rng(rngdev->base, TX4939_RNG_ROR(0));
 77			rngdev->databuf[1] =
 78				read_rng(rngdev->base, TX4939_RNG_ROR(1));
 79			rngdev->databuf[2] =
 80				read_rng(rngdev->base, TX4939_RNG_ROR(2));
 81			rngdev->data_avail =
 82				sizeof(rngdev->databuf) / sizeof(u32);
 83			/* Start RNG */
 84			write_rng(TX4939_RNG_RCSR_ST,
 85				  rngdev->base, TX4939_RNG_RCSR);
 86			wait = 0;
 87		}
 88		rng_io_end();
 89		if (!wait)
 90			break;
 91		/* 90 bus clock cycles by default for generation */
 92		ndelay(90 * 5);
 93	}
 94	return rngdev->data_avail;
 95}
 96
 97static int tx4939_rng_data_read(struct hwrng *rng, u32 *buffer)
 98{
 99	struct tx4939_rng *rngdev = container_of(rng, struct tx4939_rng, rng);
100
101	rngdev->data_avail--;
102	*buffer = *((u32 *)&rngdev->databuf + rngdev->data_avail);
103	return sizeof(u32);
104}
105
106static int __init tx4939_rng_probe(struct platform_device *dev)
107{
108	struct tx4939_rng *rngdev;
109	struct resource *r;
110	int i;
111
112	r = platform_get_resource(dev, IORESOURCE_MEM, 0);
113	if (!r)
114		return -EBUSY;
115	rngdev = devm_kzalloc(&dev->dev, sizeof(*rngdev), GFP_KERNEL);
116	if (!rngdev)
117		return -ENOMEM;
118	rngdev->base = devm_request_and_ioremap(&dev->dev, r);
119	if (!rngdev->base)
120		return -EBUSY;
121
122	rngdev->rng.name = dev_name(&dev->dev);
123	rngdev->rng.data_present = tx4939_rng_data_present;
124	rngdev->rng.data_read = tx4939_rng_data_read;
125
126	rng_io_start();
127	/* Reset RNG */
128	write_rng(TX4939_RNG_RCSR_RST, rngdev->base, TX4939_RNG_RCSR);
129	write_rng(0, rngdev->base, TX4939_RNG_RCSR);
130	/* Start RNG */
131	write_rng(TX4939_RNG_RCSR_ST, rngdev->base, TX4939_RNG_RCSR);
132	rng_io_end();
133	/*
134	 * Drop first two results.  From the datasheet:
135	 * The quality of the random numbers generated immediately
136	 * after reset can be insufficient.  Therefore, do not use
137	 * random numbers obtained from the first and second
138	 * generations; use the ones from the third or subsequent
139	 * generation.
140	 */
141	for (i = 0; i < 2; i++) {
142		rngdev->data_avail = 0;
143		if (!tx4939_rng_data_present(&rngdev->rng, 1))
144			return -EIO;
145	}
146
147	platform_set_drvdata(dev, rngdev);
148	return hwrng_register(&rngdev->rng);
149}
150
151static int __exit tx4939_rng_remove(struct platform_device *dev)
152{
153	struct tx4939_rng *rngdev = platform_get_drvdata(dev);
154
155	hwrng_unregister(&rngdev->rng);
156	platform_set_drvdata(dev, NULL);
157	return 0;
158}
159
160static struct platform_driver tx4939_rng_driver = {
161	.driver		= {
162		.name	= "tx4939-rng",
163		.owner	= THIS_MODULE,
164	},
165	.remove = tx4939_rng_remove,
166};
167
168static int __init tx4939rng_init(void)
169{
170	return platform_driver_probe(&tx4939_rng_driver, tx4939_rng_probe);
171}
172
173static void __exit tx4939rng_exit(void)
174{
175	platform_driver_unregister(&tx4939_rng_driver);
176}
177
178module_init(tx4939rng_init);
179module_exit(tx4939rng_exit);
180
181MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver for TX4939");
182MODULE_LICENSE("GPL");