juno_trng.c

/*
 * Copyright (c) 2017-2018, ARM Limited and Contributors. All rights reserved.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include <arm_acle.h>
#include <assert.h>
#include <stdbool.h>
#include <stdint.h>
#include <string.h>

#include <lib/mmio.h>
#include <lib/utils_def.h>
#include <platform_def.h>

#include <lib/smccc.h>
#include <services/trng_svc.h>
#include <smccc_helpers.h>

#include <plat/common/platform.h>

#define NSAMPLE_CLOCKS	1 /* min 1 cycle, max 231 cycles */
#define NRETRIES	5

/* initialised to false */
static bool juno_trng_initialized;

static bool output_valid(void)
{
	int i;

	for (i = 0; i < NRETRIES; i++) {
		uint32_t val;

		val = mmio_read_32(TRNG_BASE + TRNG_STATUS);
		if (val & 1U)
			return true;
	}
	return false; /* No output data available. */
}

DEFINE_SVC_UUID2(_plat_trng_uuid,
	0x23523c58, 0x7448, 0x4083, 0x9d, 0x16,
	0xe3, 0xfa, 0xb9, 0xf1, 0x73, 0xbc
);
uuid_t plat_trng_uuid;

static uint32_t crc_value = ~0U;

/*
 * Uses the Trusted Entropy Source peripheral on Juno to return 8 bytes of
 * entropy. Returns 'true' when done successfully, 'false' otherwise.
 */
bool plat_get_entropy(uint64_t *out)
{
	uint64_t ret;

	assert(out);
	assert(!check_uptr_overflow((uintptr_t)out, sizeof(*out)));

	if (!juno_trng_initialized) {
		/* Disable interrupt mode. */
		mmio_write_32(TRNG_BASE + TRNG_INTMASK, 0);
		/* Program TRNG to sample for `NSAMPLE_CLOCKS`. */
		mmio_write_32(TRNG_BASE + TRNG_CONFIG, NSAMPLE_CLOCKS);
		/* Abort any potentially pending sampling. */
		mmio_write_32(TRNG_BASE + TRNG_CONTROL, 2);
		/* Reset TRNG outputs. */
		mmio_write_32(TRNG_BASE + TRNG_STATUS, 1);

		juno_trng_initialized = true;
	}

	if (!output_valid()) {
		/* Start TRNG. */
		mmio_write_32(TRNG_BASE + TRNG_CONTROL, 1);

		if (!output_valid())
			return false;
	}

	/* CRC each two 32-bit registers together, combine the pairs */
	crc_value = __crc32w(crc_value, mmio_read_32(TRNG_BASE + 0));
	crc_value = __crc32w(crc_value, mmio_read_32(TRNG_BASE + 4));
	ret = (uint64_t)crc_value << 32;

	crc_value = __crc32w(crc_value, mmio_read_32(TRNG_BASE + 8));
	crc_value = __crc32w(crc_value, mmio_read_32(TRNG_BASE + 12));
	*out = ret | crc_value;

	/* Acknowledge current cycle, clear output registers. */
	mmio_write_32(TRNG_BASE + TRNG_STATUS, 1);
	/* Trigger next TRNG cycle. */
	mmio_write_32(TRNG_BASE + TRNG_CONTROL, 1);

	return true;
}

void plat_entropy_setup(void)
{
	uint64_t dummy;

	plat_trng_uuid = _plat_trng_uuid;

	/* Initialise the entropy source and trigger RNG generation */
	plat_get_entropy(&dummy);
}