RISC-V: virt: support poweroff/restart on tinyemu

QEMU Virt on RISC-V has syscon-reboot and syscon-poweroff compatible
devices and describes them in the device tree. TinyEMU's Virt machine
is different and has a HTIF based poweroff and no dedicated reset
mechanism. Add board support for the HTIF poweroff and use a poor man's
reset that jumps back to the reset vector.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20210916093532.21699-1-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

4 files changed, 86 insertions, 0 deletions

diff --git a/arch/riscv/Kconfig.socs b/arch/riscv/Kconfig.socs
index 5c281918d5..bd4a44a575 100644
--- a/arch/riscv/Kconfig.socs
+++ b/arch/riscv/Kconfig.socs
@@ -22,6 +22,14 @@ config SOC_VIRT
 	  Generates an image tht can be be booted by QEMU. The image is called
 	  barebox-dt-2nd.img
 
+config BOARD_RISCVEMU
+	depends on SOC_VIRT
+	bool "TinyEMU Virt Machine (riscvemu)"
+	default y
+	help
+	  TinyEMU's Virt machine differs from QEMU in poweroff and restart
+	  mechanisms. This adds the necessary support.
+
 config CPU_SIFIVE
 	bool
 	select HAS_CACHE
diff --git a/arch/riscv/boards/Makefile b/arch/riscv/boards/Makefile
index 8d5d9d4fc6..3b763ff308 100644
--- a/arch/riscv/boards/Makefile
+++ b/arch/riscv/boards/Makefile
@@ -3,3 +3,4 @@ obj-$(CONFIG_BOARD_ERIZO_GENERIC)	+= erizo/
 obj-$(CONFIG_BOARD_HIFIVE)		+= hifive/
 obj-$(CONFIG_BOARD_BEAGLEV)		+= beaglev/
 obj-$(CONFIG_BOARD_LITEX_LINUX)		+= litex-linux/
+obj-$(CONFIG_BOARD_RISCVEMU)		+= riscvemu/
diff --git a/arch/riscv/boards/riscvemu/Makefile b/arch/riscv/boards/riscvemu/Makefile
new file mode 100644
index 0000000000..dcfc2937d3
--- /dev/null
+++ b/arch/riscv/boards/riscvemu/Makefile
@@ -0,0 +1 @@
+obj-y += board.o
diff --git a/arch/riscv/boards/riscvemu/board.c b/arch/riscv/boards/riscvemu/board.c
new file mode 100644
index 0000000000..7dbf9afe4c
--- /dev/null
+++ b/arch/riscv/boards/riscvemu/board.c
@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2021 Ahmad Fatoum, Pengutronix
+ */
+
+#include <common.h>
+#include <driver.h>
+#include <poweroff.h>
+#include <restart.h>
+#include <asm/system.h>
+#include <asm/barebox-riscv.h>
+
+struct riscvemu_priv {
+	struct restart_handler rst;
+	void __noreturn (*restart)(unsigned long, void *);
+
+};
+
+#define HTIF_BASE_ADDR		IOMEM(0x40008000)
+#define HTIF_TOHOST_LOW		(HTIF_BASE_ADDR + 0)
+#define HTIF_TOHOST_HIGH	(HTIF_BASE_ADDR + 4)
+
+static void __noreturn riscvemu_poweroff(struct poweroff_handler *pwr)
+{
+	writel(1, HTIF_TOHOST_LOW);
+	writel(0, HTIF_TOHOST_HIGH);
+
+	__builtin_unreachable();
+}
+
+static void __noreturn riscvemu_restart(struct restart_handler *rst)
+{
+	struct riscvemu_priv *priv = container_of(rst, struct riscvemu_priv, rst);
+
+	/*
+	 * barebox PBL relocates itself to end of RAM early on, so unless
+	 * something explicitly scrubbed the initial PBL, we can jump back to
+	 * the reset vector to "reset".
+	 */
+	priv->restart(riscv_hartid(), barebox_riscv_boot_dtb());
+}
+
+static int riscvemu_probe(struct device_d *dev)
+{
+	struct device_node *of_chosen;
+	struct riscvemu_priv *priv;
+	u64 start;
+
+	if (of_find_compatible_node(NULL, NULL, "ucb,htif0"))
+		poweroff_handler_register_fn(riscvemu_poweroff);
+
+	of_chosen = of_find_node_by_path("/chosen");
+
+	if (of_property_read_u64(of_chosen, "riscv,kernel-start", &start))
+		return 0;
+
+	priv = xzalloc(sizeof(*priv));
+
+	priv->restart = (void *)(uintptr_t)start;
+	priv->rst.restart = riscvemu_restart;
+	priv->rst.name = "vector";
+
+	return restart_handler_register(&priv->rst);
+}
+
+static const struct of_device_id riscvemu_of_match[] = {
+	{ .compatible = "ucbbar,riscvemu-bar_dev" },
+	{ /* sentinel */ },
+};
+
+static struct driver_d riscvemu_board_driver = {
+	.name = "board-riscvemu",
+	.probe = riscvemu_probe,
+	.of_compatible = riscvemu_of_match,
+};
+device_platform_driver(riscvemu_board_driver);