On 11/09/15 02:45, David Gibson wrote: > On Thu, Sep 10, 2015 at 02:03:39PM +0200, Thomas Huth wrote: >> On 10/09/15 12:40, David Gibson wrote: >>> On Thu, Sep 10, 2015 at 09:33:21AM +0200, Thomas Huth wrote: >>>> On 09/09/15 23:10, Thomas Huth wrote: >>>>> On 08/09/15 07:15, David Gibson wrote: >>>> ... >>>>>> At this point rather than just implementing them as discrete machine >>>>>> options, I suspect it will be more maintainable to split out the >>>>>> h-random implementation as a pseudo-device with its own qdev and so >>>>>> forth. We already do similarly for the RTAS time of day functions >>>>>> (spapr-rtc). >>>>> >>>>> I gave that I try, but it does not work as expected. To be able to >>>>> specify the options, I'd need to instantiate this device with the >>>>> "-device" option, right? Something like: >>>>> >>>>> -device spapr-rng,backend=rng0,usekvm=0 >>>>> >>>>> Now this does not work when I use TYPE_SYS_BUS_DEVICE as parent class >>>>> like it is done for spapr-rtc, since the user apparently can not plug >>>>> device to this bus on machine spapr (you can also not plug an spapr-rtc >>>>> device this way!). >>>>> >>>>> The spapr-vlan, spapr-vty, etc. devices are TYPE_VIO_SPAPR_DEVICE, so I >>>>> also tried that instead, but then the rng device suddenly shows up under >>>>> /vdevice in the device tree - that's also not what we want, I guess. >>>> >>>> I did some more tests, and I think I can get this working with one small >>>> modification to spapr_vio.c >> ... >>>> i.e. when the dt_name has not been set, the device won't be added to the >>>> /vdevice device tree node. If that's acceptable, I'll continue with this >>>> approach. >>> >>> A bit hacky. >>> >>> I think it would be preferable to build it under SysBus by default, >>> like spapr-rtc. Properties can be set on the device using -global (or >>> -set, but -global is easier). >> >> If anyhow possible, I'd prefere to use "-device" for this instead, because >> >> a) it's easier to use for the user, for example you can simply use >> "-device spapr-rng,?" to get the list of properties - this >> does not seem to work with spapr-rtc (it has a "date" property >> which does not show up in the help text?) > > Actually, I don't think that's got anything to do with -device versus > otherwise. "date" doesn't appear because it's an "object" property > rather than a "qdev" property - that distinction is subtle and > confusing, yes.
At least it is not very friendly for the user ... if a configuration property does not show up in the help text, you've got to document it somewhere else or nobody will be aware of it. >> b) unlike the rtc device which is always instantiated, the rng >> device is rather optional, so it is IMHO more intuitive if >> created via the -device option. > > Hrm, that's true though. And.. we're back at the perrenial question > of what "standard" devices should be constructed by default. And what > "default" means. > > It seems to me that while the random device is optional, it should be > created by default. But with -device there's not really a way to do > that. But then again if it's constructed internally there's not > really a way to turn it off short of hacky machine options. Ugh. > >> So I'd like to give it a try with the TYPE_VIO_SPAPR_DEVICE first ... if >> you then still don't like the patches at all, I can still rework them to >> use TYPE_SYS_BUS_DEVICE instead. > > I still dislike putting it on the VIO "bus", since PAPR doesn't > consider it a VIO device. Hmm, that's also a valid point. After doing some more research, I think I've found yet another possibility (why isn't there a proper documentation/howto for all this QOM stuff ... or did I just miss it?) : Instead of using a bus, simply set parent = TYPE_DEVICE, so that it is a "bus-less" device. Seems to work fine at a first glance, so unless somebody tells me that this is a very bad idea, I'll try to rework my patches accordingly... Thomas
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