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Iglesias" , Ruslan_Ruslichenko@epam.com Subject: Re: [PATCH 00/27] hw/arm: Add generic FDT-based machine and infrastructure In-Reply-To: (Ruslan Ruslichenko's message of "Thu, 29 Jan 2026 16:39:27 +0100") References: <20260126174313.1418150-1-ruslichenko.r@gmail.com> <87ecn9aas7.fsf@draig.linaro.org> <87zf5w8v6h.fsf@draig.linaro.org> User-Agent: mu4e 1.14.0-pre1; emacs 30.1 Date: Fri, 06 Feb 2026 18:34:51 +0000 Message-ID: <87h5rtn2k4.fsf@draig.linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2a00:1450:4864:20::529; envelope-from=alex.bennee@linaro.org; helo=mail-ed1-x529.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Sender: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Ruslan Ruslichenko writes: > On Thu, Jan 29, 2026 at 1:23=E2=80=AFPM Alex Benn=C3=A9e wrote: >> >> BALATON Zoltan writes: >> >> > On Wed, 28 Jan 2026, Alex Benn=C3=A9e wrote: >> >> Ruslan Ruslichenko writes: >> >>> On Tue, Jan 27, 2026 at 11:03=E2=80=AFAM Peter Maydell wrote: >> >>>> On Mon, 26 Jan 2026 at 17:43, Ruslan Ruslichenko >> >>>> wrote: >> >>>>> >> >>>>> From: Ruslan Ruslichenko >> >>>>> >> >>>>> This patch series introduces new ARM machine model, arm-generic-fd= t, 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 d= oes >> >> 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-s3adsp18= 00') 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-s3ad= sp1800') microblaze/test_s3adsp1800.py:46: self.set_machine('petalogix-s3ad= sp1800') 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-ev= b") 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-ev= b') aarch64/test_aspeed_ast2700.py:163: self.set_machine('ast2700a1-ev= b') aarch64/test_aspeed_ast2700.py:174: self.set_machine('ast2700a1-ev= b') aarch64/test_aspeed_ast2700.py:178: self.vm.set_machine('ast2700a1= -evb,fmc-model=3Dw25q512jv') 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 Benn=C3=A9e >> Virtualisation Tech Lead @ Linaro --=20 Alex Benn=C3=A9e Virtualisation Tech Lead @ Linaro