drivers: entropy: add Atmel SAM entropy generator driver

Tested on the Atmel SAM E70 Xplained board.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

drivers/entropy/CMakeLists.txt

@@ -4,6 +4,7 @@ zephyr_library_sources_ifdef(CONFIG_ENTROPY_ESP32_RNG          entropy_esp32.c)
 zephyr_library_sources_ifdef(CONFIG_ENTROPY_MCUX_RNGA          entropy_mcux_rnga.c)
 zephyr_library_sources_ifdef(CONFIG_ENTROPY_MCUX_TRNG          entropy_mcux_trng.c)
 zephyr_library_sources_ifdef(CONFIG_ENTROPY_NRF5_RNG           entropy_nrf5.c)
+zephyr_library_sources_ifdef(CONFIG_ENTROPY_SAM_RNG            entropy_sam.c)
 zephyr_library_sources_ifdef(CONFIG_ENTROPY_STM32_RNG          entropy_stm32.c)
 zephyr_library_sources_ifdef(CONFIG_FAKE_ENTROPY_NATIVE_POSIX  fake_entropy_native_posix.c)
 zephyr_library_sources_ifdef(CONFIG_USERSPACE                  entropy_handlers.c)

drivers/entropy/Kconfig

@@ -17,6 +17,7 @@ source "drivers/entropy/Kconfig.mcux"
 source "drivers/entropy/Kconfig.stm32"
 source "drivers/entropy/Kconfig.esp32"
 source "drivers/entropy/Kconfig.nrf5"
+source "drivers/entropy/Kconfig.sam"
 source "drivers/entropy/Kconfig.native_posix"
 
 config ENTROPY_HAS_DRIVER

drivers/entropy/Kconfig.sam

@@ -0,0 +1,14 @@
+# Kconfig.sam - Atmel SAM TRNG configuration
+#
+# Copyright (c) 2018 Aurelien Jarno
+#
+# SPDX-License-Identifier: Apache-2.0
+
+menuconfig ENTROPY_SAM_RNG
+	bool "Atmel SAM MCU Family True Random Number Generator (TRNG) Driver"
+	depends on SOC_FAMILY_SAM
+	depends on ENTROPY_GENERATOR
+	select ENTROPY_HAS_DRIVER
+	select HAS_DTS_ENTROPY
+	help
+	  Enable True Random Number Generator (TRNG) driver for Atmel SAM MCUs.

drivers/entropy/entropy_sam.c

@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 2018 Aurelien Jarno
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <device.h>
+#include <entropy.h>
+#include <errno.h>
+#include <init.h>
+#include <soc.h>
+#include <string.h>
+
+struct trng_sam_dev_cfg {
+	Trng *regs;
+};
+
+#define DEV_CFG(dev) \
+	((const struct trng_sam_dev_cfg *const)(dev)->config->config_info)
+
+static int entropy_sam_wait_ready(Trng *const trng)
+{
+	/* According to the reference manual, the generator provides
+	 * one 32-bit random value every 84 peripheral clock cycles.
+	 * MCK may not be smaller than HCLK/4, so it should not take
+	 * more than 336 HCLK ticks. Assuming the CPU can do 1
+	 * instruction per HCLK the number of times to loop before
+	 * the TRNG is ready is less than 1000. And that is when
+	 * assuming the loop only takes 1 instruction. So looping a
+	 * million times should be more than enough.
+	 */
+	int timeout = 1000000;
+
+	while (!(trng->TRNG_ISR & TRNG_ISR_DATRDY)) {
+		if (timeout-- == 0) {
+			return -ETIMEDOUT;
+		}
+
+		k_yield();
+	}
+
+	return 0;
+}
+
+static int entropy_sam_get_entropy(struct device *dev, u8_t *buffer,
+				   u16_t length)
+{
+	Trng *const trng = DEV_CFG(dev)->regs;
+
+	while (length > 0) {
+		size_t to_copy;
+		u32_t value;
+		int res;
+
+		res = entropy_sam_wait_ready(trng);
+		if (res < 0) {
+			return res;
+		}
+
+		value = trng->TRNG_ODATA;
+		to_copy = min(length, sizeof(value));
+
+		memcpy(buffer, &value, to_copy);
+		buffer += to_copy;
+		length -= to_copy;
+	}
+
+	return 0;
+}
+
+static int entropy_sam_init(struct device *dev)
+{
+	Trng *const trng = DEV_CFG(dev)->regs;
+
+	/* Enable the user interface clock */
+	soc_pmc_peripheral_enable(DT_ENTROPY_SAM_TRNG_PERIPHERAL_ID);
+
+	/* Enable the TRNG */
+	trng->TRNG_CR = TRNG_CR_KEY_PASSWD | TRNG_CR_ENABLE;
+
+	return 0;
+}
+
+static const struct entropy_driver_api entropy_sam_api = {
+	.get_entropy = entropy_sam_get_entropy
+};
+
+static const struct trng_sam_dev_cfg trng_sam_cfg = {
+	.regs = (Trng *)DT_ENTROPY_SAM_TRNG_BASE_ADDRESS,
+};
+
+DEVICE_AND_API_INIT(entropy_sam, CONFIG_ENTROPY_NAME,
+		    entropy_sam_init, NULL, &trng_sam_cfg,
+		    PRE_KERNEL_1, CONFIG_KERNEL_INIT_PRIORITY_DEVICE,
+		    &entropy_sam_api);

dts/arm/atmel/same70.dtsi

@@ -252,6 +252,15 @@
 			status = "disabled";
 			label = "USBHS";
 		};
+
+		trng: random@40070000 {
+			compatible = "atmel,sam-trng";
+			reg = <0x40070000 0x4000>;
+			interrupts = <57 0>;
+			peripheral-id = <57>;
+			status = "ok";
+			label = "TRNG";
+		};
 	};
 };
 

dts/bindings/rng/atmel,sam-trng.yaml

@@ -0,0 +1,45 @@
+#
+# Copyright (c) 2018, Aurelien Jarno
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+---
+title: Atmel SAM TRNG (True Random Number Generator)
+version: 0.1
+
+description: >
+    This binding gives a base representation of the Atmel SAM RNG
+
+properties:
+    compatible:
+      type: string
+      category: required
+      description: compatible strings
+      constraint: "atmel,sam-trng"
+      generation: define
+
+    reg:
+      type: int
+      description: mmio register space
+      generation: define
+      category: required
+
+    interrupts:
+      type: compound
+      category: required
+      description: required interrupts
+      generation: define
+
+    peripheral-id:
+      type: int
+      description: peripheral ID
+      generation: define
+      category: required
+
+    label:
+      type: string
+      category: required
+      description: Human readable string describing the device (used by Zephyr for API name)
+      generation: define
+
+...

soc/arm/atmel_sam/same70/Kconfig.defconfig.series

@@ -73,4 +73,9 @@ config USB_DC_SAM
 	default y
 endif # USB
 
+if ENTROPY_GENERATOR
+config ENTROPY_SAM_RNG
+	default y
+endif # ENTROPY_GENERATOR
+
 endif # SOC_SERIES_SAME70

soc/arm/atmel_sam/same70/dts_fixup.h

@@ -128,4 +128,11 @@
 #define DT_USBHS_PERIPHERAL_ID	DT_ATMEL_SAM_USBHS_40038000_PERIPHERAL_ID
 #define DT_USBHS_RAM_BASE_ADDRESS	DT_ATMEL_SAM_USBHS_40038000_RAM_0
 
+#define DT_ENTROPY_SAM_TRNG_BASE_ADDRESS	DT_ATMEL_SAM_TRNG_40070000_BASE_ADDRESS
+#define DT_ENTROPY_SAM_TRNG_IRQ			DT_ATMEL_SAM_TRNG_40070000_IRQ_0
+#define DT_ENTROPY_SAM_TRNG_IRQ_PRI		DT_ATMEL_SAM_TRNG_40070000_IRQ_0_PRIORITY
+#define DT_ENTROPY_SAM_TRNG_PERIPHERAL_ID	DT_ATMEL_SAM_TRNG_40070000_PERIPHERAL_ID
+#define DT_ENTROPY_SAM_TRNG_NAME		DT_ATMEL_SAM_TRNG_40070000_LABEL
+#define CONFIG_ENTROPY_NAME			DT_ATMEL_SAM_TRNG_40070000_LABEL
+
 /* End of SoC Level DTS fixup file */