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 <stdbool.h> 9 #include <stdint.h> 10 #include <string.h> 11 12 #include <lib/mmio.h> 13 #include <lib/utils_def.h> 14 #include <platform_def.h> 15 16 #include "juno_decl.h" 17 18 #define NSAMPLE_CLOCKS 1 /* min 1 cycle, max 231 cycles */ 19 #define NRETRIES 5 20 21 /* initialised to false */ 22 static bool juno_trng_initialized; 23 24 static bool output_valid(void) 25 { 26 int i; 27 28 for (i = 0; i < NRETRIES; i++) { 29 uint32_t val; 30 31 val = mmio_read_32(TRNG_BASE + TRNG_STATUS); 32 if (val & 1U) 33 return true; 34 } 35 return false; /* No output data available. */ 36 } 37 38 /* 39 * This function fills `buf` with 8 bytes of entropy. 40 * It uses the Trusted Entropy Source peripheral on Juno. 41 * Returns 'true' when the buffer has been filled with entropy 42 * successfully, or 'false' otherwise. 43 */ 44 bool juno_getentropy(uint64_t *buf) 45 { 46 uint64_t ret; 47 48 assert(buf); 49 assert(!check_uptr_overflow((uintptr_t)buf, sizeof(*buf))); 50 51 if (!juno_trng_initialized) { 52 /* Disable interrupt mode. */ 53 mmio_write_32(TRNG_BASE + TRNG_INTMASK, 0); 54 /* Program TRNG to sample for `NSAMPLE_CLOCKS`. */ 55 mmio_write_32(TRNG_BASE + TRNG_CONFIG, NSAMPLE_CLOCKS); 56 /* Abort any potentially pending sampling. */ 57 mmio_write_32(TRNG_BASE + TRNG_CONTROL, 2); 58 /* Reset TRNG outputs. */ 59 mmio_write_32(TRNG_BASE + TRNG_STATUS, 1); 60 61 juno_trng_initialized = true; 62 } 63 64 if (!output_valid()) { 65 /* Start TRNG. */ 66 mmio_write_32(TRNG_BASE + TRNG_CONTROL, 1); 67 68 if (!output_valid()) 69 return false; 70 } 71 72 /* XOR each two 32-bit registers together, combine the pairs */ 73 ret = mmio_read_32(TRNG_BASE + 0); 74 ret ^= mmio_read_32(TRNG_BASE + 4); 75 ret <<= 32; 76 77 ret |= mmio_read_32(TRNG_BASE + 8); 78 ret ^= mmio_read_32(TRNG_BASE + 12); 79 *buf = ret; 80 81 /* Acknowledge current cycle, clear output registers. */ 82 mmio_write_32(TRNG_BASE + TRNG_STATUS, 1); 83 /* Trigger next TRNG cycle. */ 84 mmio_write_32(TRNG_BASE + TRNG_CONTROL, 1); 85 86 return true; 87 } 88