On Fri, Sep 11, 2015 at 11:43:02AM +0200, Alexander Graf wrote: > > > On 11.09.15 02:46, David Gibson wrote: > > On Thu, Sep 10, 2015 at 02:13:26PM +0200, Alexander Graf wrote: > >> > >> > >>> Am 10.09.2015 um 14:03 schrieb Thomas Huth <th...@redhat.com>: > >>> > >>>> 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?) > >>> > >>> 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. > >>> > >>> 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. > >> > >> Please don't use sysbus. If the vio device approach turns ugly, > >> create a new spapr hcall bus instead. We should have had that from > >> the beginning really. > > > > Ok.. why? > > > > It's a system (pseudo-)device that doesn't have any common bus > > infrastructure with anything else. Isn't that what SysBus is for? > > No, sysbus means "A device that has MMIO and/or PIO connected via a bus > I'm too lazy to model" really. These devices have neither.
Oh.
So.. where is one supposed to find that out?
> Back in the days before QOM, sysbus was our lowest common denominator,
> but now that we have TYPE_DEVICE and can branch off of that, we really
> shouldn't abuse sysbus devices for things they aren't.
So what actually is the root of the qdev tree then?
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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