On 04.03.15 16:07, Frank Blaschka wrote: > On Wed, Mar 04, 2015 at 03:49:15PM +0100, Alexander Graf wrote: >> >> >> On 04.03.15 14:44, Frank Blaschka wrote: >>> On Tue, Mar 03, 2015 at 09:38:37PM +0100, Alexander Graf wrote: >>>> >>>> >>>> On 03.03.15 14:25, Frank Blaschka wrote: >>>>> On Tue, Mar 03, 2015 at 10:33:05AM +0100, Alexander Graf wrote: >>>>>> >>>>>> >>>>>> >>>>>>> Am 03.03.2015 um 09:06 schrieb Frank Blaschka >>>>>>> <blasc...@linux.vnet.ibm.com>: >>>>>>> >>>>>>>> On Thu, Feb 26, 2015 at 04:34:06PM +0100, Alexander Graf wrote: >>>>>>>> >>>>>>>> >>>>>>>>> On 26.02.15 16:27, Frank Blaschka wrote: >>>>>>>>>> On Thu, Feb 26, 2015 at 03:39:15PM +0100, Alexander Graf wrote: >>>>>>>>>> >>>>>>>>>> >>>>>>>>>>> On 26.02.15 12:59, Frank Blaschka wrote: >>>>>>>>>>> This patch extends the current s390 pci implementation to >>>>>>>>>>> provide more flexibility in configuration of s390 specific >>>>>>>>>>> device handling. For this we had to introduce a new facility >>>>>>>>>>> (and bus) to hold devices representing information actually >>>>>>>>>>> provided by s390 firmware and I/O configuration. >>>>>>>>>>> >>>>>>>>>>> On s390 the physical structure of the pci system (bridge, bus, slot) >>>>>>>>>>> in not shown to the OS. For this the pci bridge and bus created >>>>>>>>>>> in qemu can also not be shown to the guest. The new zpci device >>>>>>>>>>> class >>>>>>>>>>> represents this abstract view on the bare pci function and allows to >>>>>>>>>>> provide s390 specific configuration attributes for it. >>>>>>>>>>> >>>>>>>>>>> Sample qemu configuration: >>>>>>>>>>> -device e1000,id=zpci1 >>>>>>>>>>> -device ne2k_pci,id=zpci2 >>>>>>>>>>> -device zpci,fid=2,uid=1248,pci_id=zpci1 >>>>>>>>>>> -device zpci,fid=17,uid=2244,pci_id=zpci2 >>>>>>>>>>> >>>>>>>>>>> A zpci device references the corresponding PCI device via device id. >>>>>>>>>>> The new design allows to define multiple host bridges and support >>>>>>>>>>> more >>>>>>>>>>> pci devices. >>>>>>>>>> >>>>>>>>>> Isn't this reverse? Shouldn't it rather be >>>>>>>>>> >>>>>>>>>> -device zpci,...,id=zpci1 >>>>>>>>>> -device e1000,bus=zpci1.0 >>>>>>>>>> >>>>>>>>>> with a limit on each virtual zpci bus to only support one device? >>>>>>>>> >>>>>>>>> Do you mean something like having multiple host bridges (providing a >>>>>>>>> pci bus >>>>>>>>> each) and limit the bus to just one device? >>>>>>>>> >>>>>>>>> -device s390-pcihost,fid=16,uid=1234 >>>>>>>>> -device s390-pcihost,fid=17,uid=5678 >>>>>>>>> -device e1000,bus=pci.0 >>>>>>>>> -device ne2k_pci,bus=pci.1 >>>>>>>>> >>>>>>>>> We also discussed this option but we don't like the idea to put >>>>>>>>> attributes >>>>>>>>> belong to the pci device to the host bridge. >>>>>>>> >>>>>>>> I guess I'm not grasping something obvious here :). What exactly are >>>>>>>> the >>>>>>>> attributes again? >>>>>>> Sorry for the late response, I was on vacation the last couple days. >>>>>>> >>>>>>> The fid and uid values are provided by microcode/io layer on the real >>>>>>> hardware. >>>>>> >>>>>> So they are arbitrary numbers? What uniqueness constraints do we have on >>>>>> them? >>>>> fid and uid must be unique within the same qemu. At a first look the >>>>> numbers are >>>>> arbitrary but our configuration folks want explicitly define a particular >>>>> fid and uid >>>>> to better support migration and pass-through scenarios. >>>> >>>> Well, at the end of the day you want to make sure they're identical on >>>> both sides, yes. >>>> >>>>>> IIUC you can only have a single pcie device behind a virtual "bus" >>>>>> anyway, so what if we just calculate uid and fid from the bus id? >>>>> I think this similar to the current implementation. We use the slot (idea >>>>> for the future was >>>>> bus + slot) to generate uid and fid. But this is not flexible enough. As >>>>> I said, our >>>>> configuration folks want to be able to specify fid and uid for the device. >>>> >>>> I don't see how this is different from what PPC does with its LIOBN >>>> which is a property of the PHB. >>>> >>>> >>>> Alex >>>> >>> >>> I played arround with the idea of having multiple host bridges and this >>> worked well >>> at least for static (non hotplug) configuration. In case I want to hotplug >>> a host >>> bridge I got following error: >>> >>> (qemu) device_add s390-pcihost,fid=8,uid=9 >>> Bus 'main-system-bus' does not support hotplugging >>> >>> Is there anything I have to enable to support this? >>> >>> I have: has_dynamic_sysbus = 1 and cannot_instantiate_with_device_add_yet = >>> false >>> but this seems not to help for the hotplug case. >> >> Having s390 devices reside on sysbus is probably a bad idea. Instead, >> they should be on an s390 specific bus which then can implement hotplug >> easily. >> >> >> Alex >> > > Hm now I get lost ... > > Do you suggest we should implement a s390 specific device (which is not > derived from > TYPE_PCI_HOST_BRIDGE) but implements a pci bus so we can attach a pci device > to this > device?
Ugh, PCI_HOST_BRIDGE is a sysbus device. Awesome. Conceptually your PCI bridge is not a sysbus device, since it doesn't live on a flat MMIO + legacy IRQ routing bus. Instead, it lives on its own thing that handles MMIO and IRQs via special backdoor interfaces. How much of the PCI_HOST_BRIDGE device are you actually using? Would it be a lot of effort to have another s390 specific device that exposes a PCIBus, but is not of type PCI_HOST_BRIDGE (and thus sysbus)? Alex