From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60314) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZaKrR-0007bl-D0 for qemu-devel@nongnu.org; Fri, 11 Sep 2015 05:43:14 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZaKrN-0005nT-AU for qemu-devel@nongnu.org; Fri, 11 Sep 2015 05:43:13 -0400 References: <1441046762-5788-2-git-send-email-thuth@redhat.com> <20150901003808.GI11475@voom.redhat.com> <55E583A6.4000600@redhat.com> <20150908050316.GA372@tungsten.ozlabs.ibm.com> <20150908051528.GD24774@voom.redhat.com> <55F0A036.2090508@redhat.com> <55F13241.8040004@redhat.com> <20150910104051.GC11781@voom> <55F1719B.5070208@redhat.com> <20150911004657.GG11781@voom> From: Alexander Graf Message-ID: <55F2A226.5040407@suse.de> Date: Fri, 11 Sep 2015 11:43:02 +0200 MIME-Version: 1.0 In-Reply-To: <20150911004657.GG11781@voom> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH v2 1/2] spapr: Add support for hwrng when available List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: Thomas Huth , "armbru@redhat.com" , "qemu-devel@nongnu.org" , "michael@ellerman.id.au" , "qemu-ppc@nongnu.org" , "amit.shah@redhat.com" , Sam Bobroff 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 : >>> >>>> 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. 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. Alex