1 /* 2 * Copyright (c) 2017-2018, ARM Limited and Contributors. All rights reserved. 3 * 4 * SPDX-License-Identifier: BSD-3-Clause 5 */ 6 7 #include <assert.h> 8 #include <mmio.h> 9 #include <string.h> 10 #include <utils_def.h> 11 #include "juno_decl.h" 12 #include "juno_def.h" 13 14 #define NSAMPLE_CLOCKS 1 /* min 1 cycle, max 231 cycles */ 15 #define NRETRIES 5 16 17 static inline int output_valid(void) 18 { 19 int i; 20 21 for (i = 0; i < NRETRIES; i++) { 22 uint32_t val; 23 24 val = mmio_read_32(TRNG_BASE + TRNG_STATUS); 25 if (val & 1U) 26 break; 27 } 28 if (i >= NRETRIES) 29 return 0; /* No output data available. */ 30 return 1; 31 } 32 33 /* 34 * This function fills `buf` with `len` bytes of entropy. 35 * It uses the Trusted Entropy Source peripheral on Juno. 36 * Returns 0 when the buffer has been filled with entropy 37 * successfully and -1 otherwise. 38 */ 39 int juno_getentropy(void *buf, size_t len) 40 { 41 uint8_t *bp = buf; 42 43 assert(buf); 44 assert(len); 45 assert(!check_uptr_overflow((uintptr_t)bp, len)); 46 47 /* Disable interrupt mode. */ 48 mmio_write_32(TRNG_BASE + TRNG_INTMASK, 0); 49 /* Program TRNG to sample for `NSAMPLE_CLOCKS`. */ 50 mmio_write_32(TRNG_BASE + TRNG_CONFIG, NSAMPLE_CLOCKS); 51 52 while (len > 0) { 53 int i; 54 55 /* Start TRNG. */ 56 mmio_write_32(TRNG_BASE + TRNG_CONTROL, 1); 57 58 /* Check if output is valid. */ 59 if (!output_valid()) 60 return -1; 61 62 /* Fill entropy buffer. */ 63 for (i = 0; i < TRNG_NOUTPUTS; i++) { 64 size_t n; 65 uint32_t val; 66 67 val = mmio_read_32(TRNG_BASE + i * sizeof(uint32_t)); 68 n = MIN(len, sizeof(uint32_t)); 69 memcpy(bp, &val, n); 70 bp += n; 71 len -= n; 72 if (len == 0) 73 break; 74 } 75 76 /* Reset TRNG outputs. */ 77 mmio_write_32(TRNG_BASE + TRNG_STATUS, 1); 78 } 79 80 return 0; 81 } 82