cpu: Add a RISC-V CPU driver

This adds a driver for RISC-V CPU. Note the driver will bind
a RISC-V timer driver if "timebase-frequency" property is
present in the device tree.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Anup Patel <anup@brainfault.org>

drivers/cpu/Kconfig

@@ -13,3 +13,9 @@ config CPU_MPC83XX
 	select CLK_MPC83XX
 	help
 	  Support CPU cores for SoCs of the MPC83xx series.
+
+config CPU_RISCV
+	bool "Enable RISC-V CPU driver"
+	depends on CPU && RISCV
+	help
+	  Support CPU cores for RISC-V architecture.

drivers/cpu/Makefile

@@ -8,4 +8,5 @@ obj-$(CONFIG_CPU) += cpu-uclass.o
 
 obj-$(CONFIG_ARCH_BMIPS) += bmips_cpu.o
 obj-$(CONFIG_CPU_MPC83XX) += mpc83xx_cpu.o
+obj-$(CONFIG_CPU_RISCV) += riscv_cpu.o
 obj-$(CONFIG_SANDBOX) += cpu_sandbox.o

drivers/cpu/riscv_cpu.c

@@ -0,0 +1,116 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2018, Bin Meng <bmeng.cn@gmail.com>
+ */
+
+#include <common.h>
+#include <cpu.h>
+#include <dm.h>
+#include <errno.h>
+#include <dm/device-internal.h>
+#include <dm/lists.h>
+
+static int riscv_cpu_get_desc(struct udevice *dev, char *buf, int size)
+{
+	const char *isa;
+
+	isa = dev_read_string(dev, "riscv,isa");
+	if (size < (strlen(isa) + 1))
+		return -ENOSPC;
+
+	strcpy(buf, isa);
+
+	return 0;
+}
+
+static int riscv_cpu_get_info(struct udevice *dev, struct cpu_info *info)
+{
+	const char *mmu;
+
+	dev_read_u32(dev, "clock-frequency", (u32 *)&info->cpu_freq);
+
+	mmu = dev_read_string(dev, "mmu-type");
+	if (!mmu)
+		info->features |= BIT(CPU_FEAT_MMU);
+
+	return 0;
+}
+
+static int riscv_cpu_get_count(struct udevice *dev)
+{
+	ofnode node;
+	int num = 0;
+
+	ofnode_for_each_subnode(node, dev_ofnode(dev->parent)) {
+		const char *device_type;
+
+		device_type = ofnode_read_string(node, "device_type");
+		if (!device_type)
+			continue;
+		if (strcmp(device_type, "cpu") == 0)
+			num++;
+	}
+
+	return num;
+}
+
+static int riscv_cpu_bind(struct udevice *dev)
+{
+	struct cpu_platdata *plat = dev_get_parent_platdata(dev);
+	struct driver *drv;
+	int ret;
+
+	/* save the hart id */
+	plat->cpu_id = dev_read_addr(dev);
+
+	/* first examine the property in current cpu node */
+	ret = dev_read_u32(dev, "timebase-frequency", &plat->timebase_freq);
+	/* if not found, then look at the parent /cpus node */
+	if (ret)
+		dev_read_u32(dev->parent, "timebase-frequency",
+			     &plat->timebase_freq);
+
+	/*
+	 * Bind riscv-timer driver on hart 0
+	 *
+	 * We only instantiate one timer device which is enough for U-Boot.
+	 * Pass the "timebase-frequency" value as the driver data for the
+	 * timer device.
+	 *
+	 * Return value is not checked since it's possible that the timer
+	 * driver is not included.
+	 */
+	if (!plat->cpu_id && plat->timebase_freq) {
+		drv = lists_driver_lookup_name("riscv_timer");
+		if (!drv) {
+			debug("Cannot find the timer driver, not included?\n");
+			return 0;
+		}
+
+		device_bind_with_driver_data(dev, drv, "riscv_timer",
+					     plat->timebase_freq, ofnode_null(),
+					     NULL);
+	}
+
+	return 0;
+}
+
+static const struct cpu_ops riscv_cpu_ops = {
+	.get_desc	= riscv_cpu_get_desc,
+	.get_info	= riscv_cpu_get_info,
+	.get_count	= riscv_cpu_get_count,
+};
+
+static const struct udevice_id riscv_cpu_ids[] = {
+	{ .compatible = "riscv" },
+	{ }
+};
+
+U_BOOT_DRIVER(riscv_cpu) = {
+	.name = "riscv_cpu",
+	.id = UCLASS_CPU,
+	.of_match = riscv_cpu_ids,
+	.bind = riscv_cpu_bind,
+	.ops = &riscv_cpu_ops,
+	.flags = DM_FLAG_PRE_RELOC,
+};