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/bitfield.h>
9 #include <linux/completion.h>
10 #include <linux/container_of.h>
11 #include <linux/errno.h>
12 #include <linux/gpio/consumer.h>
13 #include <linux/gpio/driver.h>
14 #include <linux/hw_random.h>
15 #include <linux/i2c.h>
16 #include <linux/interrupt.h>
17 #include <linux/minmax.h>
18 #include <linux/string.h>
19 #include <linux/types.h>
20
21 #include <linux/turris-omnia-mcu-interface.h>
22 #include "turris-omnia-mcu.h"
23
24 #define OMNIA_CMD_TRNG_MAX_ENTROPY_LEN 64
25
omnia_trng_irq_handler(int irq,void * dev_id)26 static irqreturn_t omnia_trng_irq_handler(int irq, void *dev_id)
27 {
28 struct omnia_mcu *mcu = dev_id;
29
30 complete(&mcu->trng_entropy_ready);
31
32 return IRQ_HANDLED;
33 }
34
omnia_trng_read(struct hwrng * rng,void * data,size_t max,bool wait)35 static int omnia_trng_read(struct hwrng *rng, void *data, size_t max, bool wait)
36 {
37 struct omnia_mcu *mcu = container_of(rng, struct omnia_mcu, trng);
38 u8 reply[1 + OMNIA_CMD_TRNG_MAX_ENTROPY_LEN];
39 int err, bytes;
40
41 if (!wait && !completion_done(&mcu->trng_entropy_ready))
42 return 0;
43
44 do {
45 if (wait_for_completion_interruptible(&mcu->trng_entropy_ready))
46 return -ERESTARTSYS;
47
48 err = omnia_cmd_read(mcu->client,
49 OMNIA_CMD_TRNG_COLLECT_ENTROPY,
50 reply, sizeof(reply));
51 if (err)
52 return err;
53
54 bytes = min3(reply[0], max, OMNIA_CMD_TRNG_MAX_ENTROPY_LEN);
55 } while (wait && !bytes);
56
57 memcpy(data, &reply[1], bytes);
58
59 return bytes;
60 }
61
omnia_mcu_register_trng(struct omnia_mcu * mcu)62 int omnia_mcu_register_trng(struct omnia_mcu *mcu)
63 {
64 struct device *dev = &mcu->client->dev;
65 u8 irq_idx, dummy;
66 int irq, err;
67
68 if (!(mcu->features & OMNIA_FEAT_TRNG))
69 return 0;
70
71 irq_idx = omnia_int_to_gpio_idx[__bf_shf(OMNIA_INT_TRNG)];
72 irq = gpiod_to_irq(gpio_device_get_desc(mcu->gc.gpiodev, irq_idx));
73 if (irq < 0)
74 return dev_err_probe(dev, irq, "Cannot get TRNG IRQ\n");
75
76 /*
77 * If someone else cleared the TRNG interrupt but did not read the
78 * entropy, a new interrupt won't be generated, and entropy collection
79 * will be stuck. Ensure an interrupt will be generated by executing
80 * the collect entropy command (and discarding the result).
81 */
82 err = omnia_cmd_read(mcu->client, OMNIA_CMD_TRNG_COLLECT_ENTROPY,
83 &dummy, 1);
84 if (err)
85 return err;
86
87 init_completion(&mcu->trng_entropy_ready);
88
89 err = devm_request_threaded_irq(dev, irq, NULL, omnia_trng_irq_handler,
90 IRQF_ONESHOT, "turris-omnia-mcu-trng",
91 mcu);
92 if (err)
93 return dev_err_probe(dev, err, "Cannot request TRNG IRQ\n");
94
95 mcu->trng.name = "turris-omnia-mcu-trng";
96 mcu->trng.read = omnia_trng_read;
97
98 err = devm_hwrng_register(dev, &mcu->trng);
99 if (err)
100 return dev_err_probe(dev, err, "Cannot register TRNG\n");
101
102 return 0;
103 }
104