esp32: drivers: Add Entropy Device tree support

- Add TRNG module to esp32.dtsi
- Updated the note about TRNG register address

Signed-off-by: Mohamed ElShahawi <ExtremeGTX@hotmail.com>

boards/xtensa/esp32/esp32.dts

@@ -70,3 +70,7 @@
 	sda-pin = <18>;
 	scl-pin = <5>;
 };
+
+&trng0 {
+	status = "okay";
+};

drivers/entropy/Kconfig.esp32

@@ -8,6 +8,7 @@ config ENTROPY_ESP32_RNG
 	bool "ESP32 entropy number generator driver"
 	depends on SOC_ESP32
 	select ENTROPY_HAS_DRIVER
+	select HAS_DTS_ENTROPY
 	help
 	  This option enables the entropy number generator for ESP32 SoCs.
 

drivers/entropy/entropy_esp32.c

@@ -9,14 +9,15 @@
 
 static inline u32_t entropy_esp32_get_u32(void)
 {
-	/* The documentation specifies the random number generator at the
-	 * following address, which is at odds with the SDK, that specifies
-	 * it at 0x60035144.  The fact that they're 0x200c0000 bytes apart
-	 * (lower 16 bits are the same) suggests this might be the same
-	 * register, just mirrored somewhere else in the address space.
-	 * Confirmation is required.
+	/*
+	 * APB Address:   0x60035144 (Safe,slower writes)
+	 * DPORT Address: 0x3ff75144 (write bug, fast writes)
+	 * In this case it won't make a difference because it is read only
+	 * More info available at:
+	 * https://www.esp32.com/viewtopic.php?f=2&t=3033&p=14227
+	 * also check: ECO and Workarounds for Bugs Document, point 3.3
 	 */
-	volatile u32_t *rng_data_reg = (u32_t *)0x3ff75144;
+	volatile u32_t *rng_data_reg = (u32_t *)DT_INST_0_ESPRESSIF_ESP32_TRNG_BASE_ADDRESS;
 
 	/* Read just once.  This is not optimal as the generator has
 	 * limited throughput due to scarce sources of entropy, specially
@@ -53,7 +54,7 @@ static struct entropy_driver_api entropy_esp32_api_funcs = {
 	.get_entropy = entropy_esp32_get_entropy
 };
 
-DEVICE_AND_API_INIT(entropy_esp32, CONFIG_ENTROPY_NAME,
+DEVICE_AND_API_INIT(entropy_esp32, DT_INST_0_ESPRESSIF_ESP32_TRNG_LABEL,
 		    entropy_esp32_init, NULL, NULL,
 		    PRE_KERNEL_1, CONFIG_KERNEL_INIT_PRIORITY_DEVICE,
 		    &entropy_esp32_api_funcs);

dts/bindings/rng/espressif,esp32-trng.yaml

@@ -0,0 +1,23 @@
+# Copyright (c) 2019, Mohamed ElShahawi <ExtremeGTX@hotmail.com>
+# SPDX-License-Identifier: Apache-2.0
+
+title: Espressif ESP32 TRNG (True Random Number Generator)
+
+description: >
+    The TRNG use the noise in the Wi-Fi/BT RF system.
+    When Wi-Fi and BT are disabled, the random number generator will give out
+    pseudo-random numbers.
+
+compatible: "espressif,esp32-trng"
+
+include: base.yaml
+
+properties:
+    reg:
+      required: true
+
+    interrupts:
+      required: false
+
+    label:
+      required: true

dts/xtensa/espressif/esp32.dtsi

@@ -92,5 +92,13 @@
 			label = "I2C_1";
 			status = "disabled";
 		};
+
+		trng0: trng@3ff75144 {
+			compatible = "espressif,esp32-trng";
+			reg = <0x3FF75144 0x4>;
+			/* interrupts = <33 0>; - FIXME: Enable interrupts when interrupt-controller got supported in device tree */
+			label = "TRNG_0";
+			status = "disabled";
+		};
 	};
 };

soc/xtensa/esp32/dts_fixup.h

@@ -7,5 +7,5 @@
 /* SoC level DTS fixup file */
 
 #define DT_CPU_CLOCK_FREQUENCY DT_CADENCE_TENSILICA_XTENSA_LX6_0_CLOCK_FREQUENCY
-
+#define CONFIG_ENTROPY_NAME DT_INST_0_ESPRESSIF_ESP32_TRNG_LABEL
 /* End of SoC Level DTS fixup file */