drivers: entropy: update espressif source

Update entropy driver to add proper ESP32-S3 waiting cycles.
Add custow ESP32C6 waiting cycles and handle LP_TIMER support.

Signed-off-by: Sylvio Alves <[email protected]>

Author: sylvioalves

drivers/entropy/entropy_esp32.c

@@ -20,6 +20,26 @@
 
 LOG_MODULE_REGISTER(entropy, CONFIG_ENTROPY_LOG_LEVEL);
 
+#if SOC_LP_TIMER_SUPPORTED
+#include "hal/lp_timer_hal.h"
+#endif
+
+#if defined CONFIG_SOC_SERIES_ESP32S3
+/* If APB clock is 80 MHz, the maximum sampling frequency is around 45 KHz */
+/* 45 KHz reading frequency is the maximum we have tested so far on S3 */
+#define APB_CYCLE_WAIT_NUM (1778)
+#elif defined CONFIG_SOC_SERIES_ESP32C6
+/* On ESP32C6, we only read one byte at a time, then XOR the value with
+ * an asynchronous timer (see code below).
+ * The current value translates to a sampling frequency of around 62.5 KHz
+ * for reading 8 bit samples, which is the rate at which the RNG was tested,
+ * plus additional overhead for the calculation, making it slower.
+ */
+#define APB_CYCLE_WAIT_NUM (160 * 16)
+#else
+#define APB_CYCLE_WAIT_NUM (16)
+#endif
+
 static inline uint32_t entropy_esp32_get_u32(void)
 {
 	/* The PRNG which implements WDEV_RANDOM register gets 2 bits
@@ -30,18 +50,29 @@ static inline uint32_t entropy_esp32_get_u32(void)
 	 * wait a bit longer due to extra time spent in arithmetic and branch statements.
 	 */
 
-	uint32_t cpu_to_apb_freq_ratio =
-		esp_clk_cpu_freq() / esp_clk_apb_freq();
+	uint32_t cpu_to_apb_freq_ratio = esp_clk_cpu_freq() / esp_clk_apb_freq();
 
 	static uint32_t last_ccount;
 	uint32_t ccount;
-
+	uint32_t result = 0;
+#if SOC_LP_TIMER_SUPPORTED
+	for (size_t i = 0; i < sizeof(result); i++) {
+		do {
+			ccount = esp_cpu_get_cycle_count();
+			result ^= REG_READ(WDEV_RND_REG);
+		} while (ccount - last_ccount < cpu_to_apb_freq_ratio * APB_CYCLE_WAIT_NUM);
+		uint32_t current_rtc_timer_counter = (lp_timer_hal_get_cycle_count() & 0xFF);
+
+		result ^= ((result ^ current_rtc_timer_counter) & 0xFF) << (i * 8);
+	}
+#else
 	do {
 		ccount = esp_cpu_get_cycle_count();
-	} while (ccount - last_ccount < cpu_to_apb_freq_ratio * 16);
+		result ^= REG_READ(WDEV_RND_REG);
+	} while (ccount - last_ccount < cpu_to_apb_freq_ratio * APB_CYCLE_WAIT_NUM);
+#endif
 	last_ccount = ccount;
-
-	return REG_READ(WDEV_RND_REG);
+	return result ^ REG_READ(WDEV_RND_REG);
 }
 
 static int entropy_esp32_get_entropy(const struct device *dev, uint8_t *buf,