drivers: entropy: Add driver for LiteX PRBS module

This adds PRBS ranom number generator driver for
LiteX SoC builder with its bindings.

Signed-off-by: Pawel Czarnecki <pczarnecki@internships.antmicro.com>
Signed-off-by: Mateusz Holenko <mholenko@antmicro.com>

CODEOWNERS

@@ -128,6 +128,7 @@
 /drivers/ps2/                             @albertofloyd @franciscomunoz @scottwcpg
 /drivers/kscan/                           @albertofloyd @franciscomunoz @scottwcpg
 /drivers/ethernet/                        @jukkar @tbursztyka @pfalcon
+/drivers/entropy/*litex*                  @mateusz-holenko @kgugala @pgielda
 /drivers/flash/                           @nashif @nvlsianpu
 /drivers/flash/*nrf*                      @nvlsianpu
 /drivers/flash/*spi_nor*                  @pabigot

drivers/entropy/CMakeLists.txt

@@ -9,6 +9,7 @@ zephyr_library_sources_ifdef(CONFIG_ENTROPY_MCUX_TRNG          entropy_mcux_trng
 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_ENTROPY_LITEX_RNG          entropy_litex.c)
 zephyr_library_sources_ifdef(CONFIG_FAKE_ENTROPY_NATIVE_POSIX  fake_entropy_native_posix.c)
 zephyr_library_sources_ifdef(CONFIG_USERSPACE                  entropy_handlers.c)
 zephyr_library_sources_ifdef(CONFIG_ENTROPY_RV32M1_TRNG        entropy_rv32m1_trng.c)

drivers/entropy/Kconfig

@@ -18,6 +18,7 @@ source "drivers/entropy/Kconfig.nrf5"
 source "drivers/entropy/Kconfig.sam"
 source "drivers/entropy/Kconfig.native_posix"
 source "drivers/entropy/Kconfig.rv32m1"
+source "drivers/entropy/Kconfig.litex"
 
 config ENTROPY_HAS_DRIVER
 	bool

drivers/entropy/Kconfig.litex

@@ -0,0 +1,13 @@
+# LiteX PRBS entropy generator driver configuration
+
+# Copyright (c) 2019 Antmicro <www.antmicro.com>
+# SPDX-License-Identifier: Apache-2.0
+
+menuconfig ENTROPY_LITEX_RNG
+	bool "PRBS RNG driver"
+	depends on SOC_RISCV32_LITEX_VEXRISCV
+	select ENTROPY_HAS_DRIVER
+	help
+	  This option enables the RNG module, which is an entropy number
+	  generator, based on Pseudo-Random Binary Sequences (PRBS)
+	  for LiteX SoC builder

drivers/entropy/entropy_litex.c

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2019 Antmicro <www.antmicro.com>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <device.h>
+#include <drivers/entropy.h>
+#include <errno.h>
+#include <init.h>
+#include <soc.h>
+#include <string.h>
+#include <zephyr.h>
+
+#define PRBS_STATUS     ((volatile uint32_t *)DT_INST_0_LITEX_PRBS_BASE_ADDRESS)
+#define PRBS_WIDTH      DT_INST_0_LITEX_PRBS_SIZE
+#define SUBREG_SIZE_BIT 8
+
+static inline unsigned int prbs_read(volatile u32_t *reg_status,
+					 volatile u32_t reg_width)
+{
+	u32_t shifted_data, shift, i;
+	u32_t result = 0;
+
+	for (i = 0; i < reg_width; ++i) {
+		shifted_data = *(reg_status + i);
+		shift = (reg_width - i - 1) * SUBREG_SIZE_BIT;
+		result |= (shifted_data << shift);
+	}
+
+	return result;
+}
+
+static int entropy_prbs_get_entropy(struct device *dev, u8_t *buffer,
+					 u16_t length)
+{
+	while (length > 0) {
+		size_t to_copy;
+		u32_t value;
+
+		value = prbs_read(PRBS_STATUS, PRBS_WIDTH);
+		to_copy = MIN(length, sizeof(value));
+
+		memcpy(buffer, &value, to_copy);
+		buffer += to_copy;
+		length -= to_copy;
+	}
+	return 0;
+}
+
+static int entropy_prbs_init(struct device *dev)
+{
+	return 0;
+}
+
+static const struct entropy_driver_api entropy_prbs_api = {
+	.get_entropy = entropy_prbs_get_entropy
+};
+
+DEVICE_AND_API_INIT(entropy_prbs, CONFIG_ENTROPY_NAME,
+		    entropy_prbs_init, NULL, NULL,
+		    PRE_KERNEL_1, CONFIG_KERNEL_INIT_PRIORITY_DEVICE,
+		    &entropy_prbs_api);
+

dts/bindings/rng/litex,prbs.yaml

@@ -0,0 +1,12 @@
+# Copyright (c) 2019 Antmicro <www.antmicro.com>
+# SPDX-License-Identifier: Apache-2.0
+
+description: LiteX PRBS
+
+compatible: "litex,prbs"
+
+include: base.yaml
+
+properties:
+    reg:
+        required: true