[PATCH 1/2] power: reset: Add QEMU virt-ctrl driver

[Kuan-Wei Chiu <visitorckw@gmail.com>]

Add a new driver for the 'virt-ctrl' device found on QEMU virt machines
(e.g. m68k). This device provides a simple interface for system reset
and power off [1].

This driver registers a restart handler for system reboot and sets the
global pm_power_off callback for system shutdown. It is designed to be
generic and can be reused by other architectures utilizing this QEMU
device.

Link: https://gitlab.com/qemu-project/qemu/-/blob/v10.2.0/hw/misc/virt_ctrl.c [1]
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
 MAINTAINERS                          |  6 ++
 drivers/power/reset/Kconfig          | 10 +++
 drivers/power/reset/Makefile         |  1 +
 drivers/power/reset/qemu-virt-ctrl.c | 98 ++++++++++++++++++++++++++++
 4 files changed, 115 insertions(+)
 create mode 100644 drivers/power/reset/qemu-virt-ctrl.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 0d044a58cbfe..2586e4162304 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -21179,6 +21179,12 @@ S:	Maintained
 F:	drivers/firmware/qemu_fw_cfg.c
 F:	include/uapi/linux/qemu_fw_cfg.h
 
+QEMU VIRT MACHINE SYSTEM CONTROLLER DRIVER
+M:	Kuan-Wei Chiu <visitorckw@gmail.com>
+L:	linux-pm@vger.kernel.org
+S:	Maintained
+F:	drivers/power/reset/qemu-virt-ctrl.c
+
 QLOGIC QL41xxx FCOE DRIVER
 M:	Saurav Kashyap <skashyap@marvell.com>
 M:	Javed Hasan <jhasan@marvell.com>
diff --git a/drivers/power/reset/Kconfig b/drivers/power/reset/Kconfig
index f6c1bcbb57de..1ca1c2913cbc 100644
--- a/drivers/power/reset/Kconfig
+++ b/drivers/power/reset/Kconfig
@@ -354,4 +354,14 @@ config POWER_MLXBF
 	help
 	  This driver supports reset or low power mode handling for Mellanox BlueField.
 
+config POWER_RESET_QEMU_VIRT_CTRL
+	bool "QEMU Virt Machine System Controller"
+	depends on HAS_IOMEM
+	help
+	  This driver supports the system reset and power off functionality
+	  provided by the QEMU 'virt-ctrl' device.
+
+	  Say Y here if you are running Linux on a QEMU virtual machine that
+	  provides this controller, such as the m68k virt machine.
+
 endif
diff --git a/drivers/power/reset/Makefile b/drivers/power/reset/Makefile
index 0e4ae6f6b5c5..d7ae97241a83 100644
--- a/drivers/power/reset/Makefile
+++ b/drivers/power/reset/Makefile
@@ -41,3 +41,4 @@ obj-$(CONFIG_SYSCON_REBOOT_MODE) += syscon-reboot-mode.o
 obj-$(CONFIG_POWER_RESET_SC27XX) += sc27xx-poweroff.o
 obj-$(CONFIG_NVMEM_REBOOT_MODE) += nvmem-reboot-mode.o
 obj-$(CONFIG_POWER_MLXBF) += pwr-mlxbf.o
+obj-$(CONFIG_POWER_RESET_QEMU_VIRT_CTRL) += qemu-virt-ctrl.o
diff --git a/drivers/power/reset/qemu-virt-ctrl.c b/drivers/power/reset/qemu-virt-ctrl.c
new file mode 100644
index 000000000000..f1acd22172ce
--- /dev/null
+++ b/drivers/power/reset/qemu-virt-ctrl.c
@@ -0,0 +1,98 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * QEMU Virt Machine System Controller Driver
+ *
+ * Copyright (C) 2026 Kuan-Wei Chiu <visitorckw@gmail.com>
+ */
+
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/reboot.h>
+
+/* Registers */
+#define VIRT_CTRL_REG_FEATURES	0x00
+#define VIRT_CTRL_REG_CMD	0x04
+
+/* Commands */
+#define CMD_NOOP	0
+#define CMD_RESET	1
+#define CMD_HALT	2
+#define CMD_PANIC	3
+
+struct qemu_virt_ctrl {
+	void __iomem *base;
+	struct notifier_block restart_nb;
+};
+
+static void __iomem *qemu_virt_ctrl_base;
+
+static void qemu_virt_ctrl_power_off(void)
+{
+	if (qemu_virt_ctrl_base)
+		iowrite32be(CMD_HALT, qemu_virt_ctrl_base + VIRT_CTRL_REG_CMD);
+}
+
+static int qemu_virt_ctrl_restart(struct notifier_block *nb, unsigned long action,
+				  void *data)
+{
+	struct qemu_virt_ctrl *vc = container_of(nb, struct qemu_virt_ctrl, restart_nb);
+
+	iowrite32be(CMD_RESET, vc->base + VIRT_CTRL_REG_CMD);
+
+	return NOTIFY_DONE;
+}
+
+static int qemu_virt_ctrl_probe(struct platform_device *pdev)
+{
+	struct qemu_virt_ctrl *vc;
+	int ret;
+
+	vc = devm_kzalloc(&pdev->dev, sizeof(*vc), GFP_KERNEL);
+	if (!vc)
+		return -ENOMEM;
+
+	vc->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(vc->base))
+		return PTR_ERR(vc->base);
+
+	qemu_virt_ctrl_base = vc->base;
+
+	vc->restart_nb.notifier_call = qemu_virt_ctrl_restart;
+	vc->restart_nb.priority = 128;
+
+	ret = register_restart_handler(&vc->restart_nb);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret,
+				     "cannot register restart handler\n");
+
+	if (!pm_power_off)
+		pm_power_off = qemu_virt_ctrl_power_off;
+
+	platform_set_drvdata(pdev, vc);
+
+	return 0;
+}
+
+static void qemu_virt_ctrl_remove(struct platform_device *pdev)
+{
+	struct qemu_virt_ctrl *vc = platform_get_drvdata(pdev);
+
+	unregister_restart_handler(&vc->restart_nb);
+
+	if (pm_power_off == qemu_virt_ctrl_power_off)
+		pm_power_off = NULL;
+}
+
+static struct platform_driver qemu_virt_ctrl_driver = {
+	.probe = qemu_virt_ctrl_probe,
+	.remove = qemu_virt_ctrl_remove,
+	.driver = {
+		.name = "qemu-virt-ctrl",
+	},
+};
+module_platform_driver(qemu_virt_ctrl_driver);
+
+MODULE_AUTHOR("Kuan-Wei Chiu <visitorckw@gmail.com>");
+MODULE_DESCRIPTION("QEMU Virt Machine System Controller Driver");
+MODULE_LICENSE("GPL");
-- 
2.52.0.457.g6b5491de43-goog