power: reset: Add QEMU virt-ctrl driver

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
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Acked-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://patch.msgid.link/20260412211952.3564033-2-visitorckw@gmail.com
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

diff --git a/MAINTAINERS b/MAINTAINERS
index 55af015174a54e17cc7449e5a80b6cdc83aa6fde..aa9eb8540637dc86366542689732708426d3815a 100644 (file)
--- 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 f6c1bcbb57deff3568d6b1b326454add3b3bbf06..99e3334726a5828dc2d5854e95198c9c1090d567 100644 (file)
--- 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 0e4ae6f6b5c55729cf60846d47e6fe0fec24f3cc..d7ae97241a838fe1b536b2f911868e7590d12e3b 100644 (file)
--- 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 (file)
index 0000000..01409df
--- /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");