On 1/11/21 3:50 PM, Luc Michel wrote: > Hi, > > We would like to work on improving QEMU to be able to create custom > machines from the command line. The goal here is to get feedback from > the community and shape the future developments.
Cc'ing John who is working on command line, and some developers from the "inter-VM device emulation interface" call. https://www.mail-archive.com/qemu-devel@nongnu.org/msg723252.html > > The use case mainly comes from people working with tools to customize > their designs, such as SiFive Core Designer > (https://scs.sifive.com/core-designer). This kind of tools may allow > creation or customization of a whole SoC, from the number of cores, to > the memory and IRQ mapping of peripherals etc. > > The ultimate goal would be to be able to create any kind of machine on > the command line. However we are aware that this is a substantial amount > of changes in QEMU. > > In its current state, QEMU allows for very limited customization of > existing machines on the command line. We identified the following > limitations (feel free to add to the list): > > - Most devices are not user creatable. Moreover, sysbus devices must > be explicitly allowed by a machine to be creatable through `-device`, > > - Memory regions cannot be created on the command line, > > - Device MMIO regions cannot be mapped on a bus from the command line, > > - GPIOs and clocks cannot be wired from the command line, > > - CPUs are not sysbus devices (and not user-creatable). They need > special care when creating them regarding system reset. Not being on a > bus means that they must be reset manually on system reset. This is done > in machines by registering a QEMU reset handler. > > - Machine specific boot code is usually hard-coded into the machine > itself. Some architectures (e.g. ARM) do factorize bootloader related > code, but there is no standard way of doing that in QEMU. > > We don't want to address all those limitations at once. We plan to start > with the following scenario: > > - Start with a base machine that would handle CPU creation and > bootloader stuff. Note that the "none" machine is probably not > sufficient in its current shape. It does allow only one CPU and > obviously does not handle the boot process. > > - Allow for this machine every sysbus devices we want to be user > command-line creatable (and mark them user_creatable if needed) > > - Add command line options to create memory regions (probably ram ones > at first) > > - Add command line options to map a memory region (including sysbus > device MMIO regions) onto another (memory_region_add_subregion) > > - Add command line options to connect GPIOs and clocks. > > This would hopefully allow for simple machines creation. We would then > be able to use either the command line or the `-readconfig` option to > create the machine. > > Note that we are not planning to use QMP/HMP for now. From our > understanding, a `device_add` request is always considered as hot-plug, > which is not what we want here. > > Please tell us what do you think about this plan. Any feedback is > appreciated. Then we can discuss the details of how to do this properly. > Thanks! > > -- > Luc >
