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 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 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 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) 74 return dev_err_probe(dev, -ENXIO, "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