rpi3: Introduce hardware RNG driver

Note that this is a non-secure RNG. This is only useful for educational
purposes.

Change-Id: If359c8d0f755ef8e416986de7fbca34679a523e1
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

plat/rpi3/rpi3_hw.h

@@ -58,6 +58,24 @@
  */
 #define RPI3_PM_RSTS_WRCFG_HALT		U(0x00000555)
 
+/*
+ * Hardware random number generator.
+ */
+#define RPI3_IO_RNG_OFFSET		ULL(0x00104000)
+#define RPI3_RNG_BASE			(RPI3_IO_BASE + RPI3_IO_RNG_OFFSET)
+#define RPI3_RNG_CTRL_OFFSET		ULL(0x00000000)
+#define RPI3_RNG_STATUS_OFFSET		ULL(0x00000004)
+#define RPI3_RNG_DATA_OFFSET		ULL(0x00000008)
+#define RPI3_RNG_INT_MASK_OFFSET	ULL(0x00000010)
+/* Enable/disable RNG */
+#define RPI3_RNG_CTRL_ENABLE		U(0x1)
+#define RPI3_RNG_CTRL_DISABLE		U(0x0)
+/* Number of currently available words */
+#define RPI3_RNG_STATUS_NUM_WORDS_SHIFT	U(24)
+#define RPI3_RNG_STATUS_NUM_WORDS_MASK	U(0xFF)
+/* Value to mask interrupts caused by the RNG */
+#define RPI3_RNG_INT_MASK_DISABLE	U(0x1)
+
 /*
  * Serial port (called 'Mini UART' in the BCM docucmentation).
  */

plat/rpi3/rpi3_private.h

@@ -33,6 +33,9 @@ uint32_t rpi3_get_spsr_for_bl33_entry(void);
 /* IO storage utility functions */
 void plat_rpi3_io_setup(void);
 
+/* Hardware RNG functions */
+void rpi3_rng_read(void *buf, size_t len);
+
 /* VideoCore firmware commands */
 int rpi3_vc_hardware_get_board_revision(uint32_t *revision);
 

plat/rpi3/rpi3_rng.c

+/*
+ * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <assert.h>
+#include <mmio.h>
+#include <string.h>
+
+#include "rpi3_hw.h"
+
+/* Initial amount of values to discard */
+#define RNG_WARMUP_COUNT	U(0x40000)
+
+static void rpi3_rng_initialize(void)
+{
+	uint32_t int_mask, ctrl;
+
+	/* Return if it is already enabled */
+	ctrl = mmio_read_32(RPI3_RNG_BASE + RPI3_RNG_CTRL_OFFSET);
+	if ((ctrl & RPI3_RNG_CTRL_ENABLE) != 0U) {
+		return;
+	}
+
+	/* Mask interrupts */
+	int_mask = mmio_read_32(RPI3_RNG_BASE + RPI3_RNG_INT_MASK_OFFSET);
+	int_mask |= RPI3_RNG_INT_MASK_DISABLE;
+	mmio_write_32(RPI3_RNG_BASE + RPI3_RNG_INT_MASK_OFFSET, int_mask);
+
+	/* Discard several values when initializing to give it time to warmup */
+	mmio_write_32(RPI3_RNG_BASE + RPI3_RNG_STATUS_OFFSET, RNG_WARMUP_COUNT);
+
+	mmio_write_32(RPI3_RNG_BASE + RPI3_RNG_CTRL_OFFSET,
+		      RPI3_RNG_CTRL_ENABLE);
+}
+
+static uint32_t rpi3_rng_get_word(void)
+{
+	size_t nwords;
+
+	do {
+		/* Get number of available words to read */
+		nwords = (mmio_read_32(RPI3_RNG_BASE + RPI3_RNG_STATUS_OFFSET)
+				       >> RPI3_RNG_STATUS_NUM_WORDS_SHIFT)
+				       & RPI3_RNG_STATUS_NUM_WORDS_MASK;
+	} while (nwords == 0U);
+
+	return mmio_read_32(RPI3_RNG_BASE + RPI3_RNG_DATA_OFFSET);
+}
+
+void rpi3_rng_read(void *buf, size_t len)
+{
+	uint32_t data;
+	size_t left = len;
+	uint32_t *dst = buf;
+
+	assert(buf != NULL);
+	assert(len != 0U);
+	assert(check_uptr_overflow((uintptr_t) buf, (uintptr_t) len) == 0);
+
+	rpi3_rng_initialize();
+
+	while (left >= sizeof(uint32_t)) {
+		data = rpi3_rng_get_word();
+		*dst++ = data;
+		left -= sizeof(uint32_t);
+	}
+
+	if (left > 0U) {
+		data = rpi3_rng_get_word();
+		memcpy(dst, &data, left);
+	}
+}