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Re: [Qemu-ppc] [RFC PATCH v3] powerpc: add PVR mask support

From: Andreas Färber
Subject: Re: [Qemu-ppc] [RFC PATCH v3] powerpc: add PVR mask support
Date: Thu, 15 Aug 2013 17:43:29 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130620 Thunderbird/17.0.7

Am 15.08.2013 17:29, schrieb Alexander Graf:
> On 15.08.2013, at 16:47, Andreas Färber wrote:
>> There is nothing wrong with finding a mask or wildcard solution to that
>> problem, I already indicated so on the original POWER+ patch. The point
>> of the whole discussion is how to get there in the least invasive way.
>> Not whether, just how.
>> I think - unlike Alex apparently - that the least invasive way is to
>> leave models as they are and to add masking support to families and KVM
>> code only.
> Not sure I understand. What is KVM specific about this?

-cpu host is, it's in kvm.c.

These patches are changing sort comparison code in translate_ppc.c
though, which is used in multiple places.

>> I'm already trying to get away from extending the
>> POWERPC_DEF* macros for Prerna's fw_name, which are starting to get a
>> big conflict point these days and a future pain if everyone extends them
>> for the feature of the day. Note that I started with reading v3, not
>> everything from the start, and am therefore not pointing fingers at
>> anyone. It may be that you were given some unfortunate suggestions and
>> too quick in implementing them.
>> When we instantiate a -cpu POWER9 then having one POWER9_vX.Y around to
>> back it doesn't really hurt. Unlike ARM's MIDR there doesn't seem to be
>> an encoding of IBM vendor or POWER family in the PVR. The macros and
>> their new implementation are not the way they are because I consider
>> them the nicest thing in the world but because the name+pvr+svr+family
>> combination made them work for the whole zoo of models we carry around
>> and started to give us some inheritance through QOM. Making the POWER7
>> family non-abstract would require the same kind of macro "overloading"
>> for POWERPC_FAMILY that I'm trying to contain for POWERPC_DEF ATM. So
>> what I am still thinking about is how to handle there being multiple
>> matches for a PVR - I am considering putting them into a list and
>> comparing values for closest match. So that if you have a v2.4 and QEMU
>> knows v2.1 and v2.3 we take v2.3 and fill in the v2.4 PVR.
> I think this goes into the wrong direction. We should have one single unified 
> scheme to model core versions and -cpu host should be able to override them 
> for a family, no? I don't see how instantiating a POWER7_v20 object on a 
> POWER7_v23 system is any improvement over instantiating a POWER7 object.

There is no one unified scheme, as we have discussed in your absence.

My point is, a) -cpu POWER7 should result in valid values and b) you
asked to have a unified macro scheme that works for all CPUs, you got
it, now instead you are asking for something that is nice to POWERx, and
we cannot make POWERx family different from the rest wrt macros unless
we break the scheme, which you specifically wanted to have, to avoid
boilerplate QOM code you said. Now you want the full customization
goodness that you were against just before! :)


P.S. Please configure your mail client to break lines. Replying is
really hard this way...

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