Re: [PATCH v6 4/8] sysreset: Add QEMU virtual system controller driver

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

Hi Heinrich,

On Fri, Jan 30, 2026 at 12:23:31PM +0100, Heinrich Schuchardt wrote:
> Kuan-Wei Chiu <visitorckw@gmail.com> schrieb am Mi., 7. Jan. 2026, 21:19:
> 
> > Introduce a new sysreset driver for the QEMU Virtual System Controller.
> > This device is found on QEMU "virt" machines (such as the m68k virt
> > target) and provides a mechanism to trigger system reset and power-off
> > events.
> >
> > The driver maps U-Boot sysreset types to the corresponding controller
> > commands:
> > - SYSRESET_WARM / SYSRESET_COLD -> VIRT_CTRL_CMD_RESET
> > - SYSRESET_POWER_OFF -> VIRT_CTRL_CMD_HALT
> >
> > Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> > ---
> > Changes in v6:
> > - Introduce new driver to replace board-file reset implementation.
> >
> >  MAINTAINERS                                |  6 +++
> >  drivers/sysreset/Kconfig                   |  8 ++++
> >  drivers/sysreset/Makefile                  |  1 +
> >  drivers/sysreset/sysreset_qemu_virt_ctrl.c | 55 ++++++++++++++++++++++
> >  include/qemu_virt_ctrl.h                   | 13 +++++
> >  5 files changed, 83 insertions(+)
> >  create mode 100644 drivers/sysreset/sysreset_qemu_virt_ctrl.c
> >  create mode 100644 include/qemu_virt_ctrl.h
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index efecb213be7..34081769ecd 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -1598,6 +1598,12 @@ S:       Maintained
> >  T:     git https://source.denx.de/u-boot/custodians/u-boot-mpc85xx.git
> >  F:     arch/powerpc/cpu/mpc85xx/
> >
> > +QEMU VIRTUAL SYSTEM CONTROLLER
> > +M:     Kuan-Wei Chiu <visitorckw@gmail.com>
> > +S:     Maintained
> > +F:     drivers/sysreset/sysreset_qemu_virt_ctrl.c
> > +F:     include/qemu_virt_ctrl.h
> > +
> >  RAW NAND
> >  M:     Dario Binacchi <dario.binacchi@amarulasolutions.com>
> >  M:     Michael Trimarchi <michael@amarulasolutions.com>
> > diff --git a/drivers/sysreset/Kconfig b/drivers/sysreset/Kconfig
> > index 0181f6cd581..120e7510f15 100644
> > --- a/drivers/sysreset/Kconfig
> > +++ b/drivers/sysreset/Kconfig
> > @@ -298,6 +298,14 @@ config SYSRESET_QCOM_PSHOLD
> >         help
> >           Add support for the system reboot on Qualcomm SoCs via PSHOLD.
> >
> > +config SYSRESET_QEMU_VIRT_CTRL
> > +       bool "QEMU Virtual System Controller support"
> > +       depends on SYSRESET
> > +       help
> > +         Enable support for the QEMU Virtual System Controller.
> > +         This device is used in QEMU machines (e.g. m68k virt) to trigger
> >
> 
> Is this specific to m68k or does it work on all QEMU architectures? If it
> works everywhere, I would not mention m68k here.

The virt-ctrl device was originally introduced in qemu for the m68k
virt machine, which remains its sole user to date. However, as the
implementation resides in hw/misc/virt_ctrl.c, I believe it was
designed to be generic and architecture-agnostic from the start.

Regards,
Kuan-Wei

> 
> On x86 QEMU we currently lack poweroff support. So this would come in handy.
> 
> Best regards
> 
> Heinrich
> 
> +         system reset and poweroff events.
> > +
> >  endif
> >
> >  endmenu
> > diff --git a/drivers/sysreset/Makefile b/drivers/sysreset/Makefile
> > index f5c78b25896..d18a5d52360 100644
> > --- a/drivers/sysreset/Makefile
> > +++ b/drivers/sysreset/Makefile
> > @@ -32,3 +32,4 @@ obj-$(CONFIG_$(PHASE_)SYSRESET_X86) += sysreset_x86.o
> >  obj-$(CONFIG_SYSRESET_RAA215300) += sysreset_raa215300.o
> >  obj-$(CONFIG_SYSRESET_QCOM_PSHOLD) += sysreset_qcom-pshold.o
> >  obj-$(CONFIG_TARGET_XTFPGA) += sysreset_xtfpga.o
> > +obj-$(CONFIG_SYSRESET_QEMU_VIRT_CTRL) += sysreset_qemu_virt_ctrl.o
> > diff --git a/drivers/sysreset/sysreset_qemu_virt_ctrl.c
> > b/drivers/sysreset/sysreset_qemu_virt_ctrl.c
> > new file mode 100644
> > index 00000000000..e7cacc9b6e9
> > --- /dev/null
> > +++ b/drivers/sysreset/sysreset_qemu_virt_ctrl.c
> > @@ -0,0 +1,55 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +/*
> > + * Copyright (C) 2025, Kuan-Wei Chiu <visitorckw@gmail.com>
> > + *
> > + * QEMU Virtual System Controller Driver
> > + */
> > +
> > +#include <dm.h>
> > +#include <qemu_virt_ctrl.h>
> > +#include <sysreset.h>
> > +#include <asm/io.h>
> > +#include <linux/err.h>
> > +
> > +/* Register offsets */
> > +#define VIRT_CTRL_REG_FEATURES  0x00
> > +#define VIRT_CTRL_REG_CMD       0x04
> > +
> > +/* Commands */
> > +#define VIRT_CTRL_CMD_NOOP      0x00
> > +#define VIRT_CTRL_CMD_RESET     0x01
> > +#define VIRT_CTRL_CMD_HALT      0x02
> > +#define VIRT_CTRL_CMD_PANIC     0x03
> > +
> > +static int qemu_virt_ctrl_request(struct udevice *dev, enum sysreset_t
> > type)
> > +{
> > +       struct qemu_virt_ctrl_plat *plat = dev_get_plat(dev);
> > +       u32 val;
> > +
> > +       switch (type) {
> > +       case SYSRESET_WARM:
> > +       case SYSRESET_COLD:
> > +               val = VIRT_CTRL_CMD_RESET;
> > +               break;
> > +       case SYSRESET_POWER_OFF:
> > +               val = VIRT_CTRL_CMD_HALT;
> > +               break;
> > +       default:
> > +               return -EPROTONOSUPPORT;
> > +       }
> > +
> > +       writel(val, plat->reg + VIRT_CTRL_REG_CMD);
> > +
> > +       return -EINPROGRESS;
> > +}
> > +
> > +static struct sysreset_ops qemu_virt_ctrl_ops = {
> > +       .request = qemu_virt_ctrl_request,
> > +};
> > +
> > +U_BOOT_DRIVER(sysreset_qemu_virt_ctrl) = {
> > +       .name = "sysreset_qemu_virt_ctrl",
> > +       .id = UCLASS_SYSRESET,
> > +       .ops = &qemu_virt_ctrl_ops,
> > +       .plat_auto = sizeof(struct qemu_virt_ctrl_plat),
> > +};
> > diff --git a/include/qemu_virt_ctrl.h b/include/qemu_virt_ctrl.h
> > new file mode 100644
> > index 00000000000..05aad82b767
> > --- /dev/null
> > +++ b/include/qemu_virt_ctrl.h
> > @@ -0,0 +1,13 @@
> > +/* SPDX-License-Identifier: GPL-2.0-or-later */
> > +/*
> > + * Copyright (C) 2025, Kuan-Wei Chiu <visitorckw@gmail.com>
> > + */
> > +
> > +#ifndef _QEMU_VIRT_CTRL_H_
> > +#define _QEMU_VIRT_CTRL_H_
> > +
> > +struct qemu_virt_ctrl_plat {
> > +       phys_addr_t reg;
> > +};
> > +
> > +#endif /* _QEMU_VIRT_CTRL_H_ */
> > --
> > 2.52.0.457.g6b5491de43-goog
> >
> >