drivers/platform/cznic/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 <[email protected]>
   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 < 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 }