On Mon, Feb 23, 2026 at 2:23 PM Alex Bennée <[email protected]> wrote:
>
> Thomas Huth <[email protected]> writes:
>
> > Hi!
> >
> > On 19/02/2026 15.48, Ruslan Ruslichenko wrote:
> >> From: Ruslan Ruslichenko <[email protected]>
> >> Add new '-hw-dtb' command-line option and corresponding
> >> MachineState property.
> >> The 'hw-dtb' option allows to specify a Device tree
> >> binary with hardware description which Qemu should
> >> emulate.
> >> Signed-off-by: Ruslan Ruslichenko <[email protected]>
> >> ---
> >> hw/core/machine.c | 19 +++++++++++++++++++
> >> include/hw/core/boards.h | 1 +
> >> qemu-options.hx | 9 +++++++++
> >> system/vl.c | 3 +++
> >> 4 files changed, 32 insertions(+)
> >> diff --git a/hw/core/machine.c b/hw/core/machine.c
> >> index d4ef620c17..affd24cd49 100644
> >> --- a/hw/core/machine.c
> >> +++ b/hw/core/machine.c
> >> @@ -363,6 +363,20 @@ static void machine_set_dtb(Object *obj, const char
> >> *value, Error **errp)
> >> ms->dtb = g_strdup(value);
> >> }
> >> +static char *machine_get_hw_dtb(Object *obj, Error **errp)
> >> +{
> >> + MachineState *ms = MACHINE(obj);
> >> +
> >> + return g_strdup(ms->hw_dtb);
> >> +}
> >> +
> >> +static void machine_set_hw_dtb(Object *obj, const char *value, Error
> >> **errp)
> >> +{
> >> + MachineState *ms = MACHINE(obj);
> >> +
> >> + ms->hw_dtb = g_strdup(value);
> >> +}
> >> +
> >> static char *machine_get_dumpdtb(Object *obj, Error **errp)
> >> {
> >> MachineState *ms = MACHINE(obj);
> >> @@ -1145,6 +1159,11 @@ static void machine_class_init(ObjectClass *oc,
> >> const void *data)
> >> object_class_property_set_description(oc, "dtb",
> >> "Linux kernel device tree file");
> >> + object_class_property_add_str(oc, "hw-dtb",
> >> + machine_get_hw_dtb, machine_set_hw_dtb);
> >> + object_class_property_set_description(oc, "hw-dtb",
> >> + "A device tree binary used to describe the hardware to
> >> QEMU");
> >
> > Do the hardware dtbs differ from the ones that are passed to the Linux
> > kernel? If not, I think you likely could use the existing "dtb"
> > property for your new feature?
>
> They have to - the normal DTB cannot define the whole system because its
> only concerned with reporting what the kernel can see to the kernel and
> not defining the whole system including what the firmware sees.
>
Yes, Indeed.
Normal DTB was explored, but there is not enough information to create
QEMU models from it.
Thus we need to have a separate device tree.
> >
> > ...
> >> diff --git a/qemu-options.hx b/qemu-options.hx
> >> index 33fcfe7ce6..1568f3ce4c 100644
> >> --- a/qemu-options.hx
> >> +++ b/qemu-options.hx
> >> @@ -4518,6 +4518,15 @@ SRST(initrd)
> >> ERST
> >> +DEF("hw-dtb", HAS_ARG, QEMU_OPTION_hw_dtb, \
> >> + "-hw-dtb file use 'file' as device tree image\n", QEMU_ARCH_ALL)
> >> +SRST
> >> +``-hw-dtb file``
> >> + Use <file> as a device tree binary (dtb) image used to create the
> >> + emulated machine. This dtb will not be passed to the kernel, use -dtb
> >> + for that.
> >> +ERST
> >
> > Please don't add any new top level options if it is not really
> > necessary. We already got too much duplicated logic in QEMU, so we try
> > to avoid this nowadays. In your case here, it should be fine to simply
> > configure the hw-dtb via the -machine property.
Agreed. As for now there is only one user of this hw option, we can move to the
arm-generic-fdt machine option itself. I'll move this for the next version.
> >
> > Thanks,
> > Thomas
>
> --
> Alex Bennée
> Virtualisation Tech Lead @ Linaro
--
BR,
Ruslan Ruslichenko
