riscv: Include syscon_power device driver in GENERIC kernel config

QEMU's RISC-V virt machine provides syscon-power and syscon-reset
devices as the means by which to shutdown and reboot. We also need to
ensure that we have attached the syscon_generic device before attaching
any syscon_power devices, and so we introduce a new riscv_syscon device
akin to aw_syscon added in r327936. Currently the SiFive test finisher
is used as the specific implementation of such a syscon device.

Reviewed by:	br, brooks (mentor), jhb (mentor)
Approved by:	br, brooks (mentor), jhb (mentor)
Obtained from:	CheriBSD
Differential Revision:	https://reviews.freebsd.org/D25725

sys/conf/files.riscv

@@ -57,6 +57,7 @@ riscv/riscv/ofw_machdep.c	optional	fdt
 riscv/riscv/plic.c		standard
 riscv/riscv/pmap.c		standard
 riscv/riscv/riscv_console.c	optional	rcons
+riscv/riscv/riscv_syscon.c	optional	ext_resources syscon riscv_syscon fdt
 riscv/riscv/sbi.c		standard
 riscv/riscv/soc.c		standard
 riscv/riscv/stack_machdep.c	optional	ddb | stack

sys/riscv/conf/GENERIC

@@ -77,6 +77,13 @@ options 	INTRNG
 # RISC-V SBI console
 device		rcons
 
+# EXT_RESOURCES pseudo devices
+options 	EXT_RESOURCES
+device		clk
+device		syscon
+device		syscon_power
+device		riscv_syscon
+
 # Bus drivers
 device		pci
 

sys/riscv/riscv/riscv_syscon.c

@@ -0,0 +1,84 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (c) 2018 Kyle Evans <kevans@FreeBSD.org>
+ * Copyright (c) 2020 Jessica Clarke <jrtc27@FreeBSD.org>
+ *
+ * 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.
+ */
+
+/*
+ * RISC-V syscon driver. Used as a generic interface by QEMU's virt machine for
+ * describing the SiFive test finisher as a power and reset controller.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/bus.h>
+#include <sys/kernel.h>
+#include <sys/module.h>
+#include <sys/mutex.h>
+#include <sys/rman.h>
+#include <machine/bus.h>
+
+#include <dev/ofw/openfirm.h>
+#include <dev/ofw/ofw_bus.h>
+#include <dev/ofw/ofw_bus_subr.h>
+
+#include <dev/extres/syscon/syscon.h>
+#include <dev/extres/syscon/syscon_generic.h>
+
+static struct ofw_compat_data compat_data[] = {
+	{"sifive,test0",	1},
+	{"sifive,test1",	1},
+	{NULL,			0}
+};
+
+static int
+riscv_syscon_probe(device_t dev)
+{
+
+	if (!ofw_bus_status_okay(dev))
+		return (ENXIO);
+	if (ofw_bus_search_compatible(dev, compat_data)->ocd_data == 0)
+		return (ENXIO);
+
+	device_set_desc(dev, "RISC-V syscon");
+	return (BUS_PROBE_DEFAULT);
+}
+
+static device_method_t riscv_syscon_methods[] = {
+	DEVMETHOD(device_probe, riscv_syscon_probe),
+
+	DEVMETHOD_END
+};
+
+DEFINE_CLASS_1(riscv_syscon, riscv_syscon_driver, riscv_syscon_methods,
+    sizeof(struct syscon_generic_softc), syscon_generic_driver);
+
+static devclass_t riscv_syscon_devclass;
+/* riscv_syscon needs to attach prior to syscon_power */
+EARLY_DRIVER_MODULE(riscv_syscon, simplebus, riscv_syscon_driver,
+    riscv_syscon_devclass, 0, 0, BUS_PASS_SCHEDULER + BUS_PASS_ORDER_LAST);
+MODULE_VERSION(riscv_syscon, 1);