tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
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linux
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}