Add simplebus-like RISC-V SoC bus.

This is required in order to probe and attach devices described under
"riscv-virtio-soc" node of DTS.

Sponsored by:	DARPA, AFRL

sys/conf/files.riscv

@@ -46,6 +46,7 @@ riscv/riscv/nexus.c		standard
 riscv/riscv/ofw_machdep.c	optional	fdt
 riscv/riscv/pmap.c		standard
 riscv/riscv/riscv_console.c	optional	rcons
+riscv/riscv/soc.c		standard
 riscv/riscv/stack_machdep.c	optional	ddb | stack
 riscv/riscv/support.S		standard
 riscv/riscv/swtch.S		standard

sys/riscv/riscv/soc.c

@@ -0,0 +1,111 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (c) 2018 Ruslan Bukin <br@bsdpad.com>
+ * All rights reserved.
+ *
+ * This software was developed by SRI International and the University of
+ * Cambridge Computer Laboratory under DARPA/AFRL contract FA8750-10-C-0237
+ * ("CTSRD"), as part of the DARPA CRASH research programme.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/kernel.h>
+#include <sys/module.h>
+
+#include <dev/fdt/simplebus.h>
+#include <dev/ofw/ofw_bus_subr.h>
+
+struct soc_softc {
+	device_t		dev;
+};
+
+static int
+soc_probe(device_t dev)
+{
+
+	if (!ofw_bus_status_okay(dev))
+		return (ENXIO);
+
+	if (!ofw_bus_is_compatible(dev, "riscv-virtio-soc"))
+		return (ENXIO);
+
+	device_set_desc(dev, "RISC-V SoC");
+
+	return (BUS_PROBE_DEFAULT);
+}
+
+static int
+soc_attach(device_t dev)
+{
+	struct soc_softc *sc;
+	phandle_t node;
+
+	sc = device_get_softc(dev);
+	sc->dev = dev;
+
+	node = ofw_bus_get_node(dev);
+	if (node == -1)
+		return (ENXIO);
+
+	simplebus_init(dev, node);
+
+	/*
+	 * Allow devices to identify.
+	 */
+	bus_generic_probe(dev);
+
+	/*
+	 * Now walk the OFW tree and attach top-level devices.
+	 */
+	for (node = OF_child(node); node > 0; node = OF_peer(node))
+		simplebus_add_device(dev, node, 0, NULL, -1, NULL);
+
+	return (bus_generic_attach(dev));
+}
+
+static int
+soc_detach(device_t dev)
+{
+
+	return (0);
+}
+
+static device_method_t soc_methods[] = {
+	DEVMETHOD(device_probe,		soc_probe),
+	DEVMETHOD(device_attach,	soc_attach),
+	DEVMETHOD(device_detach,	soc_detach),
+	DEVMETHOD_END
+};
+
+DEFINE_CLASS_1(soc, soc_driver, soc_methods, sizeof(struct soc_softc),
+    simplebus_driver);
+static devclass_t soc_devclass;
+EARLY_DRIVER_MODULE(soc, simplebus, soc_driver, soc_devclass, 0, 0,
+    BUS_PASS_INTERRUPT + BUS_PASS_ORDER_MIDDLE);
+MODULE_VERSION(soc, 1);