Ruslan Ruslichenko <[email protected]> writes:
> On Thu, Jan 29, 2026 at 1:23 PM Alex Bennée <[email protected]> wrote:
>>
>> BALATON Zoltan <[email protected]> writes:
>>
>> > On Wed, 28 Jan 2026, Alex Bennée wrote:
>> >> Ruslan Ruslichenko <[email protected]> writes:
>> >>> On Tue, Jan 27, 2026 at 11:03 AM Peter Maydell
>> >>> <[email protected]> wrote:
>> >>>> On Mon, 26 Jan 2026 at 17:43, Ruslan Ruslichenko
>> >>>> <[email protected]> wrote:
>> >>>>>
>> >>>>> From: Ruslan Ruslichenko <[email protected]>
>> >>>>>
>> >>>>> This patch series introduces new ARM machine model, arm-generic-fdt,
>> >>>>> and the underlying infrastructure required to instantiate a QEMU
>> >>>>> machine from a Device Tree.
>> >>>>
>> >>>> I'm afraid this has been a feature that has been suggested from
>> >>>> time to time, but which I don't think is workable in general.
>> >>>>
>> >>>> Device tree files are designed to provide enough information to
>> >>>> the guest kernel to allow it to find non-probeable hardware. They
>> >>>> are not designed to provide enough information to QEMU to allow
>> >>>> it to create and wire up all the hardware present on the system.
>> >>>>
>> >>>> There are specific niches where it can be made to work -- I think
>> >>>> Xilinx have or had a setup where they were generating an FPGA
>> >>>> model and a device tree and a guest kernel all from the same
>> >>>> single data source, so they could put everything necessary into
>> >>>> the dtb, for example -- but I don't think it works in the
>> >>>> general case. As one simple example, the DTB doesn't generally
>> >>>> have any information about how the Secure world works in an Arm
>> >>>> system, because Linux doesn't care about the Secure world. It
>> >>>> also doesn't usually have information that the guest OS can
>> >>>> probe for itself at runtime.
>> >>>>
>> >>>> There has been periodic discussion of more flexible user-driven
>> >>>> board creation, but that has generally been with the idea of using
>> >>>> the QMP monitor to orchestrate creation and connection of device
>> >>>> models.
>> >>>>
>> >>> I agree that a guest Device Tree is insufficient for describing a
>> >>> complete QEMU machine model.
>> >>> However, we separate the guest configuration from the machine
>> >>> definition. The -hw-dtb option allows the user to provide a
>> >>> QEMU-specific system description.
>> >>> Those hw-dtb would not be passed to Linux Guest VM.
>> >>>
>> >>> The fact that this workflow has been successfully used in production
>> >>> by AMD/Xilinx demonstrates that FDT is a feasible format.
>> >>
>> >> Where are the extensions to the FDT used for hw-dtb documented? How does
>> >> it deal with PCI devices and the Secure world?
>> >
>> > PCI devices don't need to be included in a machine description as they
>> > are not part of the machine only the PCI host is. PCI devices are
>> > plugged into the host with -device as with boards defined in C.
>>
>> But if we are talking about a general purpose HW description DSL then we
>> do need to describe systems with embedded PCI busses and soldered on PCI
>> devices.
>>
>> > For
>> > PCI devices that are instantiated by default on some machines
>> > including a node below the PCI host should likely work. I know nothing
>> > about secure world, that may need some extensions but fdt is basically
>> > describing objects and their properties so if it's one or a hierarchy
>> > of QOM objects that needs to be instantiated with defined properties
>> > it should be possible to describe it in fdt.
>>
>> OK - hence I was asking for the documentation for how this is done. You
>> can't just assert that anything can be described in DTB because its
>> original use case is purely for OS descriptions. If we want to explore
>> this series further then I would suggest including some hw-dtb's in the
>> series to replicate some of our more embedded machines in the next
>> revision.
>>
>
> Sure, we can consider more functional examples for the v2 patch series.
> Would you like to see some specific machine constructed with hw-dtb?
>
> Also answering the previous question regarding Secure world.
> We can define parent nodes in the FDT that represent Memory Region
> containers, which are then mapped into the CPU's Secure Address Space.
>
> Any child devices defined under these nodes in the FDT are automatically
> instantiated as subregions of that parent container. This ensures they
> are only visible to the Secure World.
I would suggest we pick a representative sample of non-virt machine
types to model in hw-dtb and extend the functional tests to run both. We
have these tests (trimmed of virt, pc, and q35 machines):
riscv64/test_boston.py:36: self.set_machine('boston-aia')
riscv64/test_sifive_u.py:30: self.set_machine('sifive_u')
riscv64/test_migration.py:17: self.set_machine('spike')
riscv64/test_opensbi.py:24: self.set_machine('spike')
riscv64/test_opensbi.py:28: self.set_machine('sifive_u')
sparc64/test_tuxrun.py:27: self.set_machine('sun4u')
sparc64/test_sun4u.py:28: self.set_machine('sun4u')
sparc64/test_migration.py:13: self.set_machine('sun4u')
sparc64/test_migration.py:17: self.set_machine('sun4u')
sparc64/test_migration.py:21: self.set_machine('sun4u')
mipsel/test_malta.py:41: self.set_machine('malta')
mipsel/test_malta.py:97: self.set_machine('malta')
ppc/test_74xx.py:19: self.set_machine('g3beige')
ppc/test_74xx.py:28: self.set_machine('g3beige')
ppc/test_74xx.py:37: self.set_machine('g3beige')
ppc/test_74xx.py:46: self.set_machine('g3beige')
ppc/test_74xx.py:55: self.set_machine('g3beige')
ppc/test_74xx.py:64: self.set_machine('g3beige')
ppc/test_74xx.py:73: self.set_machine('g3beige')
ppc/test_74xx.py:82: self.set_machine('g3beige')
ppc/test_74xx.py:91: self.set_machine('g3beige')
ppc/test_74xx.py:100: self.set_machine('g3beige')
ppc/test_74xx.py:109: self.set_machine('g3beige')
ppc/test_74xx.py:118: self.set_machine('g3beige')
mips64el/test_malta.py:46: self.set_machine('malta')
mips64el/test_malta.py:72: self.set_machine('malta')
mips64el/test_malta.py:145: self.set_machine('malta')
ppc/test_tuxrun.py:27: self.set_machine('ppce500')
mipsel/test_tuxrun.py:27: self.set_machine('malta')
ppc/test_bamboo.py:29: self.set_machine('bamboo')
sparc/test_sun4m.py:18: self.set_machine('SS-20')
ppc/test_replay.py:25: self.set_machine('g3beige')
ppc/test_replay.py:29: self.set_machine('mac99')
mipsel/test_replay.py:30: self.set_machine('malta')
sparc/test_replay.py:19: self.set_machine('SS-10')
mips64el/test_tuxrun.py:27: self.set_machine('malta')
mips64/test_tuxrun.py:27: self.set_machine('malta')
ppc/test_40p.py:40: self.set_machine('40p')
ppc/test_40p.py:55: self.set_machine('40p')
ppc/test_40p.py:66: self.set_machine('40p')
ppc/test_40p.py:81: self.set_machine('40p')
sparc/test_migration.py:13: self.set_machine('SS-4')
sparc/test_migration.py:17: self.set_machine('SS-5')
sparc/test_migration.py:21: self.set_machine('SS-4')
mips64el/test_replay.py:22: self.set_machine('malta')
mips64el/test_replay.py:45: self.set_machine('malta')
ppc/test_amiga.py:25: self.set_machine('amigaone')
avr/test_uno.py:21: self.set_machine('arduino-uno')
ppc/test_ppe42.py:68: self.set_machine('ppe42_machine')
avr/test_mega2560.py:38: self.set_machine('arduino-mega-2560-v3')
mips64el/test_fuloong2e.py:33: self.set_machine('fuloong2e')
mips64el/test_fuloong2e.py:54: self.set_machine('fuloong2e')
ppc/test_migration.py:13: self.set_machine('sam460ex')
ppc/test_migration.py:17: self.set_machine('sam460ex')
ppc/test_migration.py:21: self.set_machine('sam460ex')
ppc/test_mpc8544ds.py:27: self.set_machine('mpc8544ds')
ppc/test_sam460ex.py:19: self.set_machine('sam460ex')
ppc/test_mac.py:28: self.set_machine('g3beige')
ppc/test_mac.py:32: self.set_machine('mac99')
ppc/test_virtex_ml507.py:27: self.set_machine('virtex-ml507')
riscv32/test_migration.py:13: self.set_machine('spike')
riscv32/test_migration.py:21: self.set_machine('spike')
mips/test_malta.py:57: test.set_machine('malta')
mips/test_malta.py:108: self.set_machine('malta')
mips/test_malta.py:131: self.set_machine('malta')
sh4eb/test_r2d.py:18: self.set_machine('r2d')
or1k/test_sim.py:18: self.set_machine('or1k-sim')
alpha/test_replay.py:20: self.set_machine('clipper')
mips/test_tuxrun.py:27: self.set_machine('malta')
or1k/test_replay.py:19: self.set_machine('or1k-sim')
alpha/test_clipper.py:19: self.set_machine('clipper')
mips/test_replay.py:22: self.set_machine('malta')
mips/test_replay.py:43: self.set_machine('malta')
arm/test_tuxrun.py:30: self.set_machine('versatilepb')
alpha/test_migration.py:13: self.set_machine('clipper')
alpha/test_migration.py:17: self.set_machine('clipper')
alpha/test_migration.py:21: self.set_machine('clipper')
m68k/test_mcf5208evb.py:18: self.set_machine('mcf5208evb')
m68k/test_replay.py:21: self.set_machine('q800')
m68k/test_replay.py:35: self.set_machine('mcf5208evb')
arm/test_bpim2u.py:40: self.set_machine('bpim2u')
arm/test_bpim2u.py:61: self.set_machine('bpim2u')
arm/test_bpim2u.py:94: self.set_machine('bpim2u')
arm/test_bpim2u.py:142: self.set_machine('bpim2u')
rx/test_gdbsim.py:37: self.set_machine('gdbsim-r5f562n8')
rx/test_gdbsim.py:57: self.set_machine('gdbsim-r5f562n7')
m68k/test_nextcube.py:49: self.set_machine('next-cube')
m68k/test_nextcube.py:61: self.set_machine('next-cube')
s390x/test_reverse_debug.py:15: self.set_machine('s390-ccw-virtio')
arm/test_integratorcp.py:45: self.set_machine('integratorcp')
hppa/test_cdboot.py:19: self.set_machine('B160L')
m68k/test_q800.py:19: self.set_machine('q800')
hppa/test_seabios.py:27: self.set_machine('B160L')
hppa/test_seabios.py:31: self.set_machine('C3700')
arm/test_cubieboard.py:38: self.set_machine('cubieboard')
arm/test_cubieboard.py:69: self.set_machine('cubieboard')
arm/test_cubieboard.py:107: self.set_machine('cubieboard')
arm/test_realview.py:21: self.set_machine('realview-eb-mpcore')
s390x/test_pxelinux.py:56: self.set_machine('s390-ccw-virtio')
arm/test_sx1.py:40: self.set_machine('sx1')
arm/test_sx1.py:51: self.set_machine('sx1')
arm/test_sx1.py:62: self.set_machine('sx1')
arm/test_replay.py:38: self.set_machine('cubieboard')
arm/test_replay.py:60: self.set_machine('vexpress-a9')
arm/test_aspeed_ast2600_buildroot.py:25:
self.set_machine('ast2600-evb')
arm/test_aspeed_ast2600_buildroot.py:99:
self.set_machine('ast2600-evb')
arm/test_canona1100.py:27: self.set_machine('canon-a1100')
sh4/test_r2d.py:21: self.set_machine('r2d')
xtensa/test_replay.py:19: self.set_machine('lx60')
arm/test_max78000fthr.py:19: self.set_machine('max78000fthr')
arm/test_raspi2.py:42: self.set_machine('raspi2b')
arm/test_raspi2.py:68: self.set_machine('raspi2b')
microblaze/test_replay.py:20: self.set_machine('petalogix-s3adsp1800')
sh4/test_tuxrun.py:27: self.set_machine('r2d')
xtensa/test_lx60.py:18: self.set_machine('lx60')
arm/test_smdkc210.py:24: self.set_machine('smdkc210')
arm/test_microbit.py:19: self.set_machine('microbit')
arm/test_collie.py:22: self.set_machine('collie')
arm/test_quanta_gsj.py:35: self.set_machine('quanta-gsj')
arm/test_quanta_gsj.py:71: self.set_machine('quanta-gsj')
arm/test_vexpress.py:18: self.set_machine('vexpress-a9')
microblaze/test_s3adsp1800.py:29:
self.set_machine('petalogix-s3adsp1800')
microblaze/test_s3adsp1800.py:46:
self.set_machine('petalogix-s3adsp1800')
arm/test_emcraft_sf2.py:26: self.set_machine('emcraft-sf2')
arm/test_aspeed_ast1060.py:21: self.set_machine('ast1060-evb')
arm/test_aspeed_ast1060.py:35: self.vm.set_machine("ast1060-evb")
arm/test_aspeed_rainier.py:16: self.set_machine('rainier-bmc')
arm/test_aspeed_rainier.py:42: self.set_machine('rainier-bmc')
arm/test_aspeed_ast1030.py:21: self.set_machine('ast1030-evb')
arm/test_aspeed_ast1030.py:40: self.set_machine('ast1030-evb')
arm/test_aspeed_ast1030.py:72: self.vm.set_machine("ast1030-evb")
arm/test_aspeed_ast2600_sdk.py:35: self.set_machine('ast2600-evb')
arm/test_aspeed_ast2600_sdk.py:74: self.vm.set_machine("ast2600-evb")
arm/test_stellaris.py:18: self.set_machine('lm3s6965evb')
arm/test_stellaris.py:32: self.set_machine('lm3s811evb')
arm/test_migration.py:13: self.set_machine('npcm750-evb')
arm/test_migration.py:17: self.set_machine('npcm750-evb')
arm/test_migration.py:21: self.set_machine('npcm750-evb')
arm/test_aspeed_ast2500.py:19: self.set_machine('ast2500-evb')
arm/test_aspeed_ast2500.py:45: self.set_machine('ast2500-evb')
aarch64/test_raspi4.py:37: self.set_machine('raspi4b')
aarch64/test_raspi4.py:67: self.set_machine('raspi4b')
arm/test_orangepi.py:51: self.set_machine('orangepi-pc')
arm/test_orangepi.py:72: self.set_machine('orangepi-pc')
arm/test_orangepi.py:105: self.set_machine('orangepi-pc')
arm/test_orangepi.py:149: self.set_machine('orangepi-pc')
arm/test_orangepi.py:185: self.set_machine('orangepi-pc')
ppc64/test_reverse_debug.py:25: self.set_machine('pseries')
ppc64/test_reverse_debug.py:33: self.set_machine('powernv')
aarch64/test_imx8mp_evk.py:53: self.set_machine('imx8mp-evk')
ppc64/test_migration.py:14: self.set_machine('mac99')
ppc64/test_migration.py:18: self.set_machine('mac99')
ppc64/test_migration.py:22: self.set_machine('mac99')
ppc64/test_e500.py:22: self.set_machine('ppce500')
aarch64/test_raspi3.py:24: self.set_machine('raspi3b')
ppc64/test_mac99.py:23: self.set_machine('mac99')
ppc64/test_replay.py:21: self.set_machine('ppce500')
ppc64/test_replay.py:34: self.set_machine('pseries')
aarch64/test_aspeed_ast2700.py:151: self.set_machine('ast2700a1-evb')
aarch64/test_aspeed_ast2700.py:163: self.set_machine('ast2700a1-evb')
aarch64/test_aspeed_ast2700.py:174: self.set_machine('ast2700a1-evb')
aarch64/test_aspeed_ast2700.py:178:
self.vm.set_machine('ast2700a1-evb,fmc-model=w25q512jv')
aarch64/test_migration.py:13: self.set_machine('quanta-gsj')
aarch64/test_migration.py:17: self.set_machine('quanta-gsj')
aarch64/test_migration.py:21: self.set_machine('quanta-gsj')
aarch64/test_aspeed_ast2700fc.py:152: self.set_machine('ast2700fc')
aarch64/test_aspeed_ast2700fc.py:164: self.set_machine('ast2700fc')
Thinking about it Arm's sbsa-ref would be an interesting one to check
for fidelity as the firmware stack targets an explicit HW platform.
>
>> >>> In contrast, QMP usage may end up even more complex and less
>> >>> maintainable for the task of full system modeling.
>> >>> To my understanding, this would need to generate too long configs,
>> >>> which may eventually require some intermediate format by itself.
>> >>>
>> >>> I am proposing to use FDT as a serialization format to describe a
>> >>> machine configuration. Theoretically we can use other formats, like
>> >>> XML, but in my opinion FDT perfectly matches the requirements.
>> >>
>> >> The QMP interface is self-documenting and introspectable and used for
>> >> the management of QEMU including things like hotplug. It is also QOM
>> >> aware so a natural fit for dealing with the underlying QOM machinery.
>> >
>> > QOM seems to be more about operating a machine rather than defining it
>> > for which fdt is an already established common way.
>> >
>> >> Previous discussions have entertained the idea of making the parsing of
>> >> hw-dtb an external script which would then translate into QMP commands
>> >> to build up the machine.
>> >
>> > That would be possible but it seems that directly parsing fdt in QEMU
>> > could be done with very few code and with some additional support from
>> > devices the latter of which is probably also needed when trying to
>> > interactively define a machine from command line, monitor or QMP.
>>
>> I agree QMP would need some new APIs to support this - and also have
>> some examples of how to replicate the existing machines over a pure QMP
>> interface.
>>
>> >
>> > Regards,
>> > BALATON Zoltan
>>
>> --
>> Alex Bennée
>> Virtualisation Tech Lead @ Linaro
--
Alex Bennée
Virtualisation Tech Lead @ Linaro
