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// SPDX-License-Identifier: GPL-2.0
/*
* CZ.NIC's Turris Omnia MCU TRNG driver
*
* 2024 by Marek Behún <kabel@kernel.org>
*/
#include <linux/bitfield.h>
#include <linux/completion.h>
#include <linux/container_of.h>
#include <linux/errno.h>
#include <linux/gpio/consumer.h>
#include <linux/gpio/driver.h>
#include <linux/hw_random.h>
#include <linux/i2c.h>
#include <linux/interrupt.h>
#include <linux/minmax.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/turris-omnia-mcu-interface.h>
#include "turris-omnia-mcu.h"
#define OMNIA_CMD_TRNG_MAX_ENTROPY_LEN 64
static irqreturn_t omnia_trng_irq_handler(int irq, void *dev_id)
{
struct omnia_mcu *mcu = dev_id;
complete(&mcu->trng_entropy_ready);
return IRQ_HANDLED;
}
static int omnia_trng_read(struct hwrng *rng, void *data, size_t max, bool wait)
{
struct omnia_mcu *mcu = container_of(rng, struct omnia_mcu, trng);
u8 reply[1 + OMNIA_CMD_TRNG_MAX_ENTROPY_LEN];
int err, bytes;
if (!wait && !completion_done(&mcu->trng_entropy_ready))
return 0;
do {
if (wait_for_completion_interruptible(&mcu->trng_entropy_ready))
return -ERESTARTSYS;
err = omnia_cmd_read(mcu->client,
OMNIA_CMD_TRNG_COLLECT_ENTROPY,
reply, sizeof(reply));
if (err)
return err;
bytes = min3(reply[0], max, OMNIA_CMD_TRNG_MAX_ENTROPY_LEN);
} while (wait && !bytes);
memcpy(data, &reply[1], bytes);
return bytes;
}
int omnia_mcu_register_trng(struct omnia_mcu *mcu)
{
struct device *dev = &mcu->client->dev;
u8 irq_idx, dummy;
int irq, err;
if (!(mcu->features & OMNIA_FEAT_TRNG))
return 0;
irq_idx = omnia_int_to_gpio_idx[__bf_shf(OMNIA_INT_TRNG)];
irq = gpiod_to_irq(gpio_device_get_desc(mcu->gc.gpiodev, irq_idx));
if (!irq)
return dev_err_probe(dev, -ENXIO, "Cannot get TRNG IRQ\n");
/*
* If someone else cleared the TRNG interrupt but did not read the
* entropy, a new interrupt won't be generated, and entropy collection
* will be stuck. Ensure an interrupt will be generated by executing
* the collect entropy command (and discarding the result).
*/
err = omnia_cmd_read(mcu->client, OMNIA_CMD_TRNG_COLLECT_ENTROPY,
&dummy, 1);
if (err)
return err;
init_completion(&mcu->trng_entropy_ready);
err = devm_request_threaded_irq(dev, irq, NULL, omnia_trng_irq_handler,
IRQF_ONESHOT, "turris-omnia-mcu-trng",
mcu);
if (err)
return dev_err_probe(dev, err, "Cannot request TRNG IRQ\n");
mcu->trng.name = "turris-omnia-mcu-trng";
mcu->trng.read = omnia_trng_read;
err = devm_hwrng_register(dev, &mcu->trng);
if (err)
return dev_err_probe(dev, err, "Cannot register TRNG\n");
return 0;
}
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