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

[Alexey Kardashevskiy <aik@ozlabs.ru>]

Adding David to this old conversation.

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