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// 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");
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