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

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 07/08/2015 04:37 PM, Alexey Kardashevskiy wrote:
> Adding David to this old conversation.

This is the patch:
http://patchwork.ozlabs.org/patch/446544/



>
> On 03/17/2015 09:47 AM, Alexey Kardashevskiy wrote:
>> 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