blob: 505fb02667aa7206f8b6cd3aeb47890c887e64a7 [file] [log] [blame]
/*
* Copyright (c) 2017-2018, ARM Limited and Contributors. All rights reserved.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
#include <assert.h>
#include <string.h>
#include <lib/mmio.h>
#include <lib/utils_def.h>
#include "juno_decl.h"
#include "juno_def.h"
#define NSAMPLE_CLOCKS 1 /* min 1 cycle, max 231 cycles */
#define NRETRIES 5
static inline int 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)
break;
}
if (i >= NRETRIES)
return 0; /* No output data available. */
return 1;
}
/*
* This function fills `buf` with `len` bytes of entropy.
* It uses the Trusted Entropy Source peripheral on Juno.
* Returns 0 when the buffer has been filled with entropy
* successfully and -1 otherwise.
*/
int juno_getentropy(void *buf, size_t len)
{
uint8_t *bp = buf;
assert(buf);
assert(len);
assert(!check_uptr_overflow((uintptr_t)bp, len));
/* 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);
while (len > 0) {
int i;
/* Start TRNG. */
mmio_write_32(TRNG_BASE + TRNG_CONTROL, 1);
/* Check if output is valid. */
if (!output_valid())
return -1;
/* Fill entropy buffer. */
for (i = 0; i < TRNG_NOUTPUTS; i++) {
size_t n;
uint32_t val;
val = mmio_read_32(TRNG_BASE + i * sizeof(uint32_t));
n = MIN(len, sizeof(uint32_t));
memcpy(bp, &val, n);
bp += n;
len -= n;
if (len == 0)
break;
}
/* Reset TRNG outputs. */
mmio_write_32(TRNG_BASE + TRNG_STATUS, 1);
}
return 0;
}