On 09/10/2014 12:09 PM, Alexander Graf wrote: > > > On 10.09.14 12:05, Paolo Bonzini wrote: >> Il 10/09/2014 11:56, Alexander Graf ha scritto: >>> >>> >>> On 10.09.14 11:43, Paolo Bonzini wrote: >>>> Il 10/09/2014 11:31, Alexander Graf ha scritto: >>>>>>> Yeah, please do the registration in sysbus.c, not in virt.c. There is >>>>>>> no reason to make the platform_bus_init_notify+DynSysbusNotifier >>>>>>> interface public. The code in sysbus.c can fill in the fields. >>>>> Sysbus != Platform bus. Sysbus is an in-QEMU representation of a >>>>> pseudo-bus that we put all devices onto that we consider unsorted. >>>>> >>>>> Platform bus is a machine representation of an actual bus that devices >>>>> are attached to. These devices usually are sysbus devices. >>>> >>>> Is there any difference between the two? >>>> >>>> Take a machine that has two chips, a SoC that does everything except >>>> USB, and a USB controller chip. >>>> >>>> Strictly speaking the USB controller chip would be on a "platform bus", >>>> but we would likely put it on sysbus. >>>> >>>> Why should it matter whether the devices are static or dynamic, for the >>>> sake of calling something the "system" or the "platform" bus? I would >>>> say that QEMU calls "sysbus" the platform bus. >>>> >>>> Some devices (e.g. the local APIC in x86, or the in-core timers and GIC >>>> in ARM) should probably not be in sysbus at all, and should attach >>>> directly to the CPU address space. But that is a quirk in the modeling >>>> of those devices, it shouldn't mean that sysbus is not a "platform" bus. >>> >>> On e500 for example, we have a predefined CCSR region. That is a machine >>> defined "platform bus". The offsets inside that region are strictly >>> defined by the spec. >>> >>> Now take the serial ports. We have space for 2 serial ports inside of >>> that CCSR region. We can spawn these 2 ports in the machine file based >>> on -serial, but if you want to spawn them with -device, how do you tell >>> the machine whether they should go into the "big bucket platform bus" or >>> the "CCSR platform bus"? >> >> Two possibilities: >> >> 1) you would use two instances of sysbus (one default, one created by >> the board) and specify ",bus=ccsr" on the command line when you want to >> add the device to the CCSR region. >> >> The two would work exactly the same way, only with different algorithms >> for resource allocation. >> >> 2) similar to ISA, you would create a new ccsr-bus device and a new >> ccsr-serial device, and use -device ccsr-serial,index=[0|1],chardev=foo >> to specify which of the two serial ports this is for. Most of the fdt >> magic could be shared by the sysbus and CCSR cases. >> >> I think I prefer (2)... > > Fair enough. > > As far as moving "platform bus" logic into sysbus, I'd really like to > hold back and see what this whole thing ends up getting used for first. > > So for now, I'd definitely prefer to keep "platform bus" logic and > "sysbus" logic separate. If we realize that every user only ever uses > the dynamic sysbus creation in conjunction with our "platform bus" > implementation, we can merge them. Hi Paolo, Alex, I understand I keep the code in a separate module from sysbus.c. Is that the shared conclusion? Thanks Best Regards Eric > > > Alex > _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
