[PATCH 0/2] Add QEMU virt-ctrl driver and update m68k virt

[PATCH 0/2] Add QEMU virt-ctrl driver and update m68k virt

[Kuan-Wei Chiu]

Introduce a generic platform driver for the QEMU 'virt-ctrl' device [1]
and transitions the m68k 'virt' machine to use it, replacing
architecture-specific hooks.

The new driver ('qemu-virt-ctrl') registers a restart handler and
populates the global 'pm_power_off' callback.

On the m68k side, the platform initialization is updated to register
the 'qemu-virt-ctrl' platform device. Additionally, the 'mach_reset'
hook is bridged to 'do_kernel_restart()' to ensure the kernel's restart
handler chain is correctly invoked.

Verified on QEMU m68k virt. Both system reset and power-off were
confirmed functional by invoking 'reboot(LINUX_REBOOT_CMD_RESTART)' and
'reboot(LINUX_REBOOT_CMD_POWER_OFF)' from userspace.

Link: https://gitlab.com/qemu-project/qemu/-/blob/v10.2.0/hw/misc/virt_ctrl.c [1]

Kuan-Wei Chiu (2):
  power: reset: Add QEMU virt-ctrl driver
  m68k: virt: Switch to qemu-virt-ctrl driver

 MAINTAINERS                          |  6 ++
 arch/m68k/virt/config.c              | 42 +-----------
 arch/m68k/virt/platform.c            | 20 +++++-
 drivers/power/reset/Kconfig          | 10 +++
 drivers/power/reset/Makefile         |  1 +
 drivers/power/reset/qemu-virt-ctrl.c | 98 ++++++++++++++++++++++++++++
 6 files changed, 133 insertions(+), 44 deletions(-)
 create mode 100644 drivers/power/reset/qemu-virt-ctrl.c

-- 
2.52.0.457.g6b5491de43-goog

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

[Kuan-Wei Chiu]

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

[PATCH 2/2] m68k: virt: Switch to qemu-virt-ctrl driver

[Kuan-Wei Chiu]

Register the "qemu-virt-ctrl" platform device during board
initialization to utilize the new generic power/reset driver.

Consequently, remove the legacy reset and power-off implementations
specific to the virt machine. The platform's mach_reset callback is
updated to call do_kernel_restart(), bridging the legacy m68k reboot
path to the generic kernel restart handler framework for this machine.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
 arch/m68k/virt/config.c   | 42 +--------------------------------------
 arch/m68k/virt/platform.c | 20 ++++++++++++++++---
 2 files changed, 18 insertions(+), 44 deletions(-)

diff --git a/arch/m68k/virt/config.c b/arch/m68k/virt/config.c
index 632ba200ad42..b338e2a8da6a 100644
--- a/arch/m68k/virt/config.c
+++ b/arch/m68k/virt/config.c
@@ -13,18 +13,6 @@
 
 struct virt_booter_data virt_bi_data;
 
-#define VIRT_CTRL_REG_FEATURES	0x00
-#define VIRT_CTRL_REG_CMD	0x04
-
-static struct resource ctrlres;
-
-enum {
-	CMD_NOOP,
-	CMD_RESET,
-	CMD_HALT,
-	CMD_PANIC,
-};
-
 static void virt_get_model(char *str)
 {
 	/* str is 80 characters long */
@@ -33,25 +21,9 @@ static void virt_get_model(char *str)
 		(u8)(virt_bi_data.qemu_version >> 16),
 		(u8)(virt_bi_data.qemu_version >> 8));
 }
-
-static void virt_halt(void)
-{
-	void __iomem *base = (void __iomem *)virt_bi_data.ctrl.mmio;
-
-	iowrite32be(CMD_HALT, base + VIRT_CTRL_REG_CMD);
-	local_irq_disable();
-	while (1)
-		;
-}
-
 static void virt_reset(void)
 {
-	void __iomem *base = (void __iomem *)virt_bi_data.ctrl.mmio;
-
-	iowrite32be(CMD_RESET, base + VIRT_CTRL_REG_CMD);
-	local_irq_disable();
-	while (1)
-		;
+	do_kernel_restart(NULL);
 }
 
 /*
@@ -113,20 +85,8 @@ void __init config_virt(void)
 		 virt_bi_data.tty.mmio);
 	setup_earlycon(earlycon);
 
-	ctrlres = (struct resource)
-		   DEFINE_RES_MEM_NAMED(virt_bi_data.ctrl.mmio, 0x100,
-					"virtctrl");
-
-	if (request_resource(&iomem_resource, &ctrlres)) {
-		pr_err("Cannot allocate virt controller resource\n");
-		return;
-	}
-
 	mach_init_IRQ = virt_init_IRQ;
 	mach_sched_init = virt_sched_init;
 	mach_get_model = virt_get_model;
 	mach_reset = virt_reset;
-	mach_halt = virt_halt;
-
-	register_platform_power_off(virt_halt);
 }
diff --git a/arch/m68k/virt/platform.c b/arch/m68k/virt/platform.c
index 1560c4140ab9..764f556b4b32 100644
--- a/arch/m68k/virt/platform.c
+++ b/arch/m68k/virt/platform.c
@@ -30,7 +30,10 @@ static int __init virt_platform_init(void)
 		DEFINE_RES_MEM(virt_bi_data.rtc.mmio + 0x1000, 0x1000),
 		DEFINE_RES_IRQ(virt_bi_data.rtc.irq + 1),
 	};
-	struct platform_device *pdev1, *pdev2;
+	const struct resource virt_ctrl_res[] = {
+		DEFINE_RES_MEM(virt_bi_data.ctrl.mmio, 0x100),
+	};
+	struct platform_device *pdev1, *pdev2, *pdev3;
 	struct platform_device *pdevs[VIRTIO_BUS_NB];
 	unsigned int i;
 	int ret = 0;
@@ -57,19 +60,30 @@ static int __init virt_platform_init(void)
 		goto err_unregister_tty;
 	}
 
+	pdev3 = platform_device_register_simple("qemu-virt-ctrl",
+						PLATFORM_DEVID_NONE,
+						virt_ctrl_res,
+						ARRAY_SIZE(virt_ctrl_res));
+	if (IS_ERR(pdev3)) {
+		ret = PTR_ERR(pdev3);
+		goto err_unregister_rtc;
+	}
+
 	for (i = 0; i < VIRTIO_BUS_NB; i++) {
 		pdevs[i] = virt_virtio_init(i);
 		if (IS_ERR(pdevs[i])) {
 			ret = PTR_ERR(pdevs[i]);
-			goto err_unregister_rtc_virtio;
+			goto err_unregister_virtio;
 		}
 	}
 
 	return 0;
 
-err_unregister_rtc_virtio:
+err_unregister_virtio:
 	while (i > 0)
 		platform_device_unregister(pdevs[--i]);
+	platform_device_unregister(pdev3);
+err_unregister_rtc:
 	platform_device_unregister(pdev2);
 err_unregister_tty:
 	platform_device_unregister(pdev1);
-- 
2.52.0.457.g6b5491de43-goog

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

[Daniel Palmer]

Hi Kuan-Wei,

On Tue, 13 Jan 2026 at 03:27, Kuan-Wei Chiu <visitorckw@gmail.com> wrote:
>
> 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>

FWIW: I have a driver for this in my "m68k with devicetree" tree. As
far as I could tell the virt_ctrl thing in QEMU might get more
features aside from power control.
So I made it a misc device instead.

Cheers,

Daniel

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

[Kuan-Wei Chiu]

Hi Daniel,

On Wed, Jan 14, 2026 at 07:01:58PM +0900, Daniel Palmer wrote:
> Hi Kuan-Wei,
> 
> On Tue, 13 Jan 2026 at 03:27, Kuan-Wei Chiu <visitorckw@gmail.com> wrote:
> >
> > 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>
> 
> FWIW: I have a driver for this in my "m68k with devicetree" tree. As
> far as I could tell the virt_ctrl thing in QEMU might get more
> features aside from power control.
> So I made it a misc device instead.

Thanks for the note.
Just out of curious, are there currently specific plans to add
non-power features to virt_ctrl?

If new features are added, shouldn't they be exposed via separate
drivers in their respective subsystems, rather than consolidating
everything into a misc driver?

Regards,
Kuan-Wei

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

[Daniel Palmer]

Hi Kuan-Wei,

On Thu, 15 Jan 2026 at 15:15, Kuan-Wei Chiu <visitorckw@gmail.com> wrote:

> > FWIW: I have a driver for this in my "m68k with devicetree" tree. As
> > far as I could tell the virt_ctrl thing in QEMU might get more
> > features aside from power control.
> > So I made it a misc device instead.
>
> Thanks for the note.
> Just out of curious, are there currently specific plans to add
> non-power features to virt_ctrl?

The docs here suggest that power control is the only currently
implemented feature but doesn't have to be the only feature:
https://github.com/qemu/qemu/blob/master/docs/specs/virt-ctlr.rst

> If new features are added, shouldn't they be exposed via separate
> drivers in their respective subsystems, rather than consolidating
> everything into a misc driver?

I guess if it did get new features maybe it'd be a multifunction
device? Since nothing except power control has ever actually been
implemented, maybe the way you have it right now makes the most sense.

Thanks,

Daniel

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

[Kuan-Wei Chiu]

Hi Daniel,

On Thu, Jan 15, 2026 at 10:29:29PM +0900, Daniel Palmer wrote:
> Hi Kuan-Wei,
> 
> On Thu, 15 Jan 2026 at 15:15, Kuan-Wei Chiu <visitorckw@gmail.com> wrote:
> 
> > > FWIW: I have a driver for this in my "m68k with devicetree" tree. As
> > > far as I could tell the virt_ctrl thing in QEMU might get more
> > > features aside from power control.
> > > So I made it a misc device instead.
> >
> > Thanks for the note.
> > Just out of curious, are there currently specific plans to add
> > non-power features to virt_ctrl?
> 
> The docs here suggest that power control is the only currently
> implemented feature but doesn't have to be the only feature:
> https://github.com/qemu/qemu/blob/master/docs/specs/virt-ctlr.rst
> 
> > If new features are added, shouldn't they be exposed via separate
> > drivers in their respective subsystems, rather than consolidating
> > everything into a misc driver?
> 
> I guess if it did get new features maybe it'd be a multifunction
> device? Since nothing except power control has ever actually been
> implemented, maybe the way you have it right now makes the most sense.
> 
I agree that migrating to an MFD architecture would be the right move
if/when qemu implements additional features. For now, I will stick to
the current approach in drivers/power/reset as it fits the existing
functionality best.

Thanks again for your feedback.

Regards,
Kuan-Wei

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

[Sebastian Reichel]

[-- Attachment #1: Type: text/plain, Size: 5911 bytes --]

Hi,

On Mon, Jan 12, 2026 at 06:22:56PM +0000, Kuan-Wei Chiu wrote:
> 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");

Please use devm_register_sys_off_handler().

> +	if (!pm_power_off)
> +		pm_power_off = qemu_virt_ctrl_power_off;

same.

> +	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");

You mark this as module_platform_driver() and add MODULE_*, but the
Kconfig option is bool. To be usable as a module it is missing setup
of .id_table in the platform_driver struct for auto-loading.

Greetings,

-- Sebastian

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