On Mon, 27 Apr 2015 15:57:04 +0200 Alexander Graf <ag...@suse.de> wrote:
> On 04/24/2015 11:07 AM, Cornelia Huck wrote: > > On Wed, 22 Apr 2015 14:21:36 +0200 > > Alexander Graf <ag...@suse.de> wrote: > > > >> > >>> Am 22.04.2015 um 13:40 schrieb Cornelia Huck <cornelia.h...@de.ibm.com>: > >>> > >>> On Wed, 22 Apr 2015 11:14:40 +0200 > >>> Alexander Graf <ag...@suse.de> wrote: > >>> > >>>>> On 04/22/2015 10:25 AM, Cornelia Huck wrote: > >>>>> On Tue, 21 Apr 2015 21:06:42 +0200 > >>>>> Alexander Graf <ag...@suse.de> wrote: > >>>>> > >>>>>>> On 04/17/2015 09:52 AM, Cornelia Huck wrote: > >>>>>>> From: Xu Wang <gesa...@linux.vnet.ibm.com> > >>>>>>> > >>>>>>> We have to enable this flag to support dynamically adding devices to > >>>>>>> the > >>>>>>> sysbus. This change is needed for the the upcoming diag288 watchdog. > >>>>>> s390 doesn't have a "sysbus" per se. Please create a new bus type. > >>>>> So what's wrong with the sysbus? I don't see why we should be different > >>>>> than everyone else. > >>>> The idea behind sysbus is that you have MMIO, PIO and IRQ pins > >>>> connecting to a PIC. It provides a lot of infrastructure for those > >>>> interfaces. S390 doesn't use any of them and instead wants registration > >>>> on "diag" interfaces for example which I'd put on the same layer as PIO > >>>> or MMIO registration. > >>> I don't think a "diag" bus makes sense. > >> You don't need a bus necessarily, just a parent class. > >> > >>> The individual diagnoses are > >>> way too heterogenous beyond the fact that they use the same base > >>> instruction. > >>> > >>> So where's the proper place for "misc" devices? My impression was that > >>> they can go on the sysbus. > >>> > >> If you really don't want to create your own class, how about you inherit > >> from the DeviceState class? > > I tried that for the watchdog, and it certainly works, but some things > > end up odd: > > > > - in 'info qtree', the watchdog device does not show up at all > > Please try "info qom-tree". Andreas also has a patch outstanding that > shows properties along the way with a verbose switch. While it does show up in info qom-tree, is hiding it from info qtree a good idea? I'd think that it is still widely used. > > > - in the list of devices printed by "-device help", diag288 is now the > > only device without any bus > > But it's not attached to a bus, so that's reasonable, no? Hm. Are there bus-less devices on other platforms? > > > I would have thought that any device not attached to a specialized bus > > should end up on the main system bus, which brings me back to adding it > > as a sysbus device ;) > > Not really, sysbus is QEMU's wording for what Linux calls "platform > bus". It's where devices go to that are attached to MMIO/PIO/IRQ lines > via some fabric that we don't model. But in practice sysbus seems to be more like a catch-all: On s390x, there are already things like the flic, various sclp-related devices, the virtio bridges or the ipl device sitting on the sysbus. Should they really be thrown out from the sysbus and dangle as bus-less devices? I think there is a case to be made for a catch-all bus, even if it is not the sysbus. > > The target for devices that are not the above we now have non-bus'ed > devices. I'm afraid I can't parse that sentence :)
