Re: [Qemu-devel] [RFC PATCH] target-ppc: Register CPU class per family only when needed

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 03/16/2015 09:40 PM, Andreas Färber wrote:
> Am 16.03.2015 um 05:58 schrieb Alexey Kardashevskiy:
>> On 03/06/2015 12:17 AM, Alexander Graf wrote:
>>> On 05.03.15 02:56, Alexey Kardashevskiy wrote:
>>>> At the moment when running in KVM mode, QEMU registers "host" class to
>>>> match the current CPU PVR value. It also registers another CPU class
>>>> with a CPU family name os if we run QEMU on POWER7 machine, "host" and
>>>> "POWER7" classes are created, this way we can always use "-cpu POWER7"
>>>> on the actual POWER7 machine.
>>>>
>>>> The existing code uses DeviceClass::desc field of the CPU class as
>>>> a source for the class name; it was pointed out that it is wrong to use
>>>> user-visible string as a type name.
>>>>
>>>> This adds a common CPU class name into PowerPCCPUClass struct.
>>>> This makes registration of a CPU named after the family conditional -
>>>> PowerPCCPUClass::common_cpu_name has to be non-zero. Only POWER7/POWER8
>>>> families have this field initialized by now.
>>>>
>>>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>>>
>>> LGTM. Andreas, do you agree?
>>
>>
>> Ping?
>
> No, I don't agree. Inventing a new class field just to distinguish
> POWER7/POWER8 here seems like a weird idea,

As weird as PVR itself :)

> and the code placement is not fixed either.

What is wrong with the code placement?


> I gathered that you want -cpu POWER7 and -cpu POWER8 to work on POWER8
> hardware and -cpu POWER7 on POWER7, for migration purposes, correct?
>
> What exact PVRs have you tested on and why does it not work without
> those types despite the PVR masking? To investigate I need a test case.

The real host is 003f 0201. -cpu POWER7 will fail without my patches as 
POWER7 is alias of 003f 0203.

Or real host 004b 0201 - -cpu POWER8 will try 004d 0100 and fail.


> Is this just a question of the generic family type being abstract and
> needing an updated PVR value?

May be. That could help too I suppose.

> Which other fields are actually used?

Sorry, used where? :)



-- 
Alexey