turris-omnia-mcu-trng.c

 1// SPDX-License-Identifier: GPL-2.0
 2/*
 3 * CZ.NIC's Turris Omnia MCU TRNG driver
 4 *
 5 * 2024 by Marek Behún <kabel@kernel.org>
 6 */
 7
 8#include <linux/completion.h>
 9#include <linux/container_of.h>
10#include <linux/errno.h>
11#include <linux/hw_random.h>
12#include <linux/i2c.h>
13#include <linux/interrupt.h>
14#include <linux/minmax.h>
15#include <linux/string.h>
16#include <linux/types.h>
17
18#include <linux/turris-omnia-mcu-interface.h>
19#include "turris-omnia-mcu.h"
20
21#define OMNIA_CMD_TRNG_MAX_ENTROPY_LEN	64
22
23static irqreturn_t omnia_trng_irq_handler(int irq, void *dev_id)
24{
25	struct omnia_mcu *mcu = dev_id;
26
27	complete(&mcu->trng_entropy_ready);
28
29	return IRQ_HANDLED;
30}
31
32static int omnia_trng_read(struct hwrng *rng, void *data, size_t max, bool wait)
33{
34	struct omnia_mcu *mcu = container_of(rng, struct omnia_mcu, trng);
35	u8 reply[1 + OMNIA_CMD_TRNG_MAX_ENTROPY_LEN];
36	int err, bytes;
37
38	if (!wait && !completion_done(&mcu->trng_entropy_ready))
39		return 0;
40
41	do {
42		if (wait_for_completion_interruptible(&mcu->trng_entropy_ready))
43			return -ERESTARTSYS;
44
45		err = omnia_cmd_read(mcu->client,
46				     OMNIA_CMD_TRNG_COLLECT_ENTROPY,
47				     reply, sizeof(reply));
48		if (err)
49			return err;
50
51		bytes = min3(reply[0], max, OMNIA_CMD_TRNG_MAX_ENTROPY_LEN);
52	} while (wait && !bytes);
53
54	memcpy(data, &reply[1], bytes);
55
56	return bytes;
57}
58
59int omnia_mcu_register_trng(struct omnia_mcu *mcu)
60{
61	struct device *dev = &mcu->client->dev;
62	u8 dummy;
63	int err;
64
65	if (!(mcu->features & OMNIA_FEAT_TRNG))
66		return 0;
67
68	/*
69	 * If someone else cleared the TRNG interrupt but did not read the
70	 * entropy, a new interrupt won't be generated, and entropy collection
71	 * will be stuck. Ensure an interrupt will be generated by executing
72	 * the collect entropy command (and discarding the result).
73	 */
74	err = omnia_cmd_read(mcu->client, OMNIA_CMD_TRNG_COLLECT_ENTROPY,
75			     &dummy, 1);
76	if (err)
77		return err;
78
79	init_completion(&mcu->trng_entropy_ready);
80
81	err = omnia_mcu_request_irq(mcu, OMNIA_INT_TRNG, omnia_trng_irq_handler,
82				    "turris-omnia-mcu-trng");
83	if (err)
84		return dev_err_probe(dev, err, "Cannot request TRNG IRQ\n");
85
86	mcu->trng.name = "turris-omnia-mcu-trng";
87	mcu->trng.read = omnia_trng_read;
88
89	err = devm_hwrng_register(dev, &mcu->trng);
90	if (err)
91		return dev_err_probe(dev, err, "Cannot register TRNG\n");
92
93	return 0;
94}