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88 lines
2.0 KiB
88 lines
2.0 KiB
/*
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* Copyright (c) 2017-2018, ARM Limited and Contributors. All rights reserved.
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*
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* SPDX-License-Identifier: BSD-3-Clause
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*/
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#include <assert.h>
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#include <stdbool.h>
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#include <stdint.h>
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#include <string.h>
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#include <lib/mmio.h>
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#include <lib/utils_def.h>
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#include <platform_def.h>
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#include "juno_decl.h"
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#define NSAMPLE_CLOCKS 1 /* min 1 cycle, max 231 cycles */
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#define NRETRIES 5
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/* initialised to false */
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static bool juno_trng_initialized;
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static bool output_valid(void)
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{
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int i;
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for (i = 0; i < NRETRIES; i++) {
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uint32_t val;
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val = mmio_read_32(TRNG_BASE + TRNG_STATUS);
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if (val & 1U)
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return true;
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}
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return false; /* No output data available. */
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}
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/*
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* This function fills `buf` with 8 bytes of entropy.
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* It uses the Trusted Entropy Source peripheral on Juno.
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* Returns 'true' when the buffer has been filled with entropy
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* successfully, or 'false' otherwise.
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*/
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bool juno_getentropy(uint64_t *buf)
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{
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uint64_t ret;
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assert(buf);
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assert(!check_uptr_overflow((uintptr_t)buf, sizeof(*buf)));
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if (!juno_trng_initialized) {
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/* Disable interrupt mode. */
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mmio_write_32(TRNG_BASE + TRNG_INTMASK, 0);
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/* Program TRNG to sample for `NSAMPLE_CLOCKS`. */
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mmio_write_32(TRNG_BASE + TRNG_CONFIG, NSAMPLE_CLOCKS);
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/* Abort any potentially pending sampling. */
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mmio_write_32(TRNG_BASE + TRNG_CONTROL, 2);
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/* Reset TRNG outputs. */
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mmio_write_32(TRNG_BASE + TRNG_STATUS, 1);
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juno_trng_initialized = true;
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}
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if (!output_valid()) {
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/* Start TRNG. */
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mmio_write_32(TRNG_BASE + TRNG_CONTROL, 1);
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if (!output_valid())
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return false;
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}
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/* XOR each two 32-bit registers together, combine the pairs */
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ret = mmio_read_32(TRNG_BASE + 0);
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ret ^= mmio_read_32(TRNG_BASE + 4);
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ret <<= 32;
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ret |= mmio_read_32(TRNG_BASE + 8);
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ret ^= mmio_read_32(TRNG_BASE + 12);
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*buf = ret;
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/* Acknowledge current cycle, clear output registers. */
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mmio_write_32(TRNG_BASE + TRNG_STATUS, 1);
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/* Trigger next TRNG cycle. */
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mmio_write_32(TRNG_BASE + TRNG_CONTROL, 1);
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return true;
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}
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