On 23 July 2013 13:34, Paolo Bonzini <pbonz...@redhat.com> wrote: > Il 23/07/2013 14:22, Peter Maydell ha scritto: >> On 23 July 2013 13:19, Paolo Bonzini <pbonz...@redhat.com> wrote: >>> Il 22/07/2013 20:21, Peter Maydell ha scritto >>>> you can't as a user of this sort of hardware >>>> plug in an extra serial port to a SoC, because there's just nowhere >>>> to plug it in. So why should it be possible to plug an extra >>>> serial port into the QEMU model of the SoC? >>> >>> And why exactly should QEMU be limited to modeling an existing SoC? >>> >>> Perhaps the user is not working with an existing SoC. They are working >>> with with IP building blocks that they can combine the way they prefer, >>> and they haven't yet made up their mind on the exact set of devices >>> they'll have. (because not all the world is a PC, but then not all the >>> non-PC world is ARM either). >> >> This sounds like (a) a good thing (b) something that will >> turn into an incredible incomprehensible mess if we try >> to specify it on the command line. Why would we want to do that? > > It is an incomprehensible mess on the command line, but it is actually > quite fine if you use "-readconfig" instead.
Well, the justification for this whole new bus appears to be "so you can easily just add a new device on the command line". >>> Perhaps the user can plug daughterboards that connect to the SoC and add >>> an extra serial port, visible as yet another MMIO device. >> >> Pluggable daughterboards should be implemented by actually >> defining the bus/socket that exists between the mainboard >> and the daughterboard, so you could say -device my-daughterboard >> and have it plug in to the mainboard. > > The bus might just be the processor's data bus + the interrupt > controller's pins, basically the same as sysbus. Yes, we should have easy support for defining a pluggable bus as a collection of pins. > In fact, the main thing I dislike about Alex's patch is adding a new bus > instead of making sysbus devices "just work" as pluggable devices. Agreed, more or less. Actually I'd rather sysbus devices went away -- the requirement for interrupt and GPIO and memory regions to all be defined as single arrays (so you have to know what interrupt line 3 happens to be, and that memory region 1 is the registers, and so on) is pretty unfriendly. We should be able to define all these as named connections. -- PMM
