[PATCH v4 1/2] power: reset: Add QEMU virt-ctrl driver

Kuan-Wei Chiu
2026-04-12T21:20:12Z

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 utilizes the modern system-off API to register callbacks
for both system restart and power off. It also registers a reboot
notifier to catch SYS_HALT events, ensuring that LINUX_REBOOT_CMD_HALT
is properly handled. 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>
Acked-by: Sebastian Reichel <sebastian.reichel@collabora.com>
---
Changes in v4:
- Fix sparse warning caught by kernel test robot.
- Pass the struct qemu_virt_ctrl context to sys-off handlers instead of
the __iomem pointer.

MAINTAINERS | 6 ++
drivers/power/reset/Kconfig | 10 +++
drivers/power/reset/Makefile | 1 +
drivers/power/reset/qemu-virt-ctrl.c | 122 +++++++++++++++++++++++++++
4 files changed, 139 insertions(+)
create mode 100644 drivers/power/reset/qemu-virt-ctrl.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 55af015174a5..aa9eb8540637 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -21441,6 +21441,12 @@ 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..99e3334726a5 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
+ tristate "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..01409dfe2265
--- /dev/null
+++ b/drivers/power/reset/qemu-virt-ctrl.c
@@ -0,0 +1,122 @@
+// 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/mod_devicetable.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 reboot_nb;
+};
+
+static inline void virt_ctrl_write32(u32 val, void __iomem *addr)
+{
+ if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
+ iowrite32be(val, addr);
+ else
+ iowrite32(val, addr);
+}
+
+static int qemu_virt_ctrl_power_off(struct sys_off_data *data)
+{
+ struct qemu_virt_ctrl *ctrl = data->cb_data;
+
+ virt_ctrl_write32(CMD_HALT, ctrl->base + VIRT_CTRL_REG_CMD);
+
+ return NOTIFY_DONE;
+}
+
+static int qemu_virt_ctrl_restart(struct sys_off_data *data)
+{
+ struct qemu_virt_ctrl *ctrl = data->cb_data;
+
+ virt_ctrl_write32(CMD_RESET, ctrl->base + VIRT_CTRL_REG_CMD);
+
+ return NOTIFY_DONE;
+}
+
+static int qemu_virt_ctrl_reboot_notify(struct notifier_block *nb,
+ unsigned long action, void *data)
+{
+ struct qemu_virt_ctrl *ctrl = container_of(nb, struct qemu_virt_ctrl, reboot_nb);
+
+ if (action == SYS_HALT)
+ virt_ctrl_write32(CMD_HALT, ctrl->base + VIRT_CTRL_REG_CMD);
+
+ return NOTIFY_DONE;
+}
+
+static int qemu_virt_ctrl_probe(struct platform_device *pdev)
+{
+ struct qemu_virt_ctrl *ctrl;
+ int ret;
+
+ ctrl = devm_kzalloc(&pdev->dev, sizeof(*ctrl), GFP_KERNEL);
+ if (!ctrl)
+ return -ENOMEM;
+
+ ctrl->base = devm_platform_ioremap_resource(pdev, 0);
+ if (IS_ERR(ctrl->base))
+ return PTR_ERR(ctrl->base);
+
+ ret = devm_register_sys_off_handler(&pdev->dev,
+ SYS_OFF_MODE_RESTART,
+ SYS_OFF_PRIO_DEFAULT,
+ qemu_virt_ctrl_restart,
+ ctrl);
+ if (ret)
+ return dev_err_probe(&pdev->dev, ret,
+ "cannot register restart handler\n");
+
+ ret = devm_register_sys_off_handler(&pdev->dev,
+ SYS_OFF_MODE_POWER_OFF,
+ SYS_OFF_PRIO_DEFAULT,
+ qemu_virt_ctrl_power_off,
+ ctrl);
+ if (ret)
+ return dev_err_probe(&pdev->dev, ret,
+ "cannot register power-off handler\n");
+
+ ctrl->reboot_nb.notifier_call = qemu_virt_ctrl_reboot_notify;
+ ret = devm_register_reboot_notifier(&pdev->dev, &ctrl->reboot_nb);
+ if (ret)
+ return dev_err_probe(&pdev->dev, ret, "cannot register reboot notifier\n");
+
+ return 0;
+}
+
+static const struct platform_device_id qemu_virt_ctrl_id[] = {
+ { "qemu-virt-ctrl", 0 },
+ { }
+};
+MODULE_DEVICE_TABLE(platform, qemu_virt_ctrl_id);
+
+static struct platform_driver qemu_virt_ctrl_driver = {
+ .probe = qemu_virt_ctrl_probe,
+ .driver = {
+ .name = "qemu-virt-ctrl",
+ },
+ .id_table = qemu_virt_ctrl_id,
+};
+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");
--
2.53.0.1213.gd9a14994de-goog