On 24 March 2017 at 13:48, Eduardo Habkost <ehabk...@redhat.com> wrote: > The problem with today's mechanism is that we have no way to make > a machine accept one type of sysbus device without making it > start accepting every other sysbus devices. If we thought all > !cannot_instantiate_with_device_add_yet sysbus devices were > already safe, we wouldn't have has_dynamic_sysbus in the first > place, would we?
Almost all sysbus devices are not dynamically instantiable and never will be because they need to map mmio and wire up IRQs and so on, and we have no mechanism for doing that. So the default position is "no, you can't do that (but maybe a subclass which knows better might override)". has_dynamic_sysbus is a dodgy hack for boards which support the "platform bus" which is a special case where the user can use -device for certain sysbus devices that the platform bus knows about and can wire up itself (in a range of irqs and memory that the board has set aside for that purpose). The default is still "no, you can't dynamically instantiate this", but instead of this (and the handful of exceptions) being imposed at compile time it's imposed (with exceptions) at runtime. So for instance the ARM 'virt' board sets has_dynamic_sysbus, which allows a few devices to be added with -device, but most still do not permit it (they'll end up hitting the error_report() in hw/arm/sysbus-fdt.c:add_fdt_node()). thanks -- PMM
