73 lines
1.8 KiB
C
73 lines
1.8 KiB
C
/*
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* Copyright (c) 2017 Intel Corporation
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#define DT_DRV_COMPAT espressif_esp32_trng
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#include <string.h>
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#include <soc/rtc.h>
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#include <soc/wdev_reg.h>
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#include <esp_system.h>
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#include <soc.h>
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#include <esp_cpu.h>
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#include <zephyr/drivers/entropy.h>
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static inline uint32_t entropy_esp32_get_u32(void)
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{
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/* The PRNG which implements WDEV_RANDOM register gets 2 bits
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* of extra entropy from a hardware randomness source every APB clock cycle
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* (provided WiFi or BT are enabled). To make sure entropy is not drained
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* faster than it is added, this function needs to wait for at least 16 APB
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* clock cycles after reading previous word. This implementation may actually
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* wait a bit longer due to extra time spent in arithmetic and branch statements.
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*/
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uint32_t cpu_to_apb_freq_ratio =
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esp_clk_cpu_freq() / esp_clk_apb_freq();
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static uint32_t last_ccount;
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uint32_t ccount;
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do {
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ccount = esp_cpu_get_cycle_count();
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} while (ccount - last_ccount < cpu_to_apb_freq_ratio * 16);
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last_ccount = ccount;
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return REG_READ(WDEV_RND_REG);
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}
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static int entropy_esp32_get_entropy(const struct device *dev, uint8_t *buf,
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uint16_t len)
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{
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assert(buf != NULL);
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uint8_t *buf_bytes = buf;
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while (len > 0) {
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uint32_t word = entropy_esp32_get_u32();
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uint32_t to_copy = MIN(sizeof(word), len);
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memcpy(buf_bytes, &word, to_copy);
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buf_bytes += to_copy;
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len -= to_copy;
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}
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return 0;
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}
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static int entropy_esp32_init(const struct device *dev)
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{
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/* clock initialization handled by clock manager */
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return 0;
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}
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static const struct entropy_driver_api entropy_esp32_api_funcs = {
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.get_entropy = entropy_esp32_get_entropy
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};
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DEVICE_DT_INST_DEFINE(0,
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entropy_esp32_init, NULL, NULL, NULL,
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PRE_KERNEL_1, CONFIG_ENTROPY_INIT_PRIORITY,
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&entropy_esp32_api_funcs);
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