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");