[PATCH] powerpc: Add support for VRSAVE

[Chris Johns]

On 6/9/2022 3:38 pm, Sebastian Huber wrote:
> On 06/09/2022 07:29, Chris Johns wrote:
>> On 5/9/2022 4:36 pm, Sebastian Huber wrote:
>>> On 03/09/2022 01:17, Chris Johns wrote:
>>>> On 2/9/2022 2:27 pm, Sebastian Huber wrote:
>>>>> On 02.09.22 06:22, Sebastian Huber wrote:
>>>>>> On 02.09.22 04:22, Chris Johns wrote:
>>>>>>> On 1/9/2022 6:26 pm, Sebastian Huber wrote:
>>>>>>>> The VRSAVE feature of the Altivec unit can be used to reduce the amount of
>>>>>>>> Altivec registers which need to be saved/restored during interrupt
>>>>>>>> processing
>>>>>>>> and context switches.
>>>>>>> Which BSPs and hardware has this been tested on?
>>>>>> The e6500 QoIQ BSPs.
>>>>> I mean QorIQ. We have this code since 2020 in production code. I just
>>>>> forgot to
>>>>> integrate it.
>>>> I would like to have this tested on some of the older MVME boards. Do you still
>>>> have the mvme5500 (I think)? I can look at testing in an mvme2703 this week.
>>>
>>> This will not work out of the box. In order to use the VRSAVE optimization, you
>>> need also a corresponding multilib (-mvrsave), see GCC patch. The MVME BSPs use
>>> a different exception and context switch code for the AltiVec support. You would
>>> have to convert them first to the implementation used by the QorIQ BSPs. Lastly,
>>> you also have add the -mvrsave flag to the ABI_FLAGS.
>>
>> Thank you for the explanation. This was not apparent to me so maybe something in
>> the commit message to help anyone reviewing the change would help?
> 
> Ok, I can add something to the commit message.
> 

Thanks

>>
>> Which BSPs does this effect?
> 
> Only the QorIQ BSPs using the e6500 core and only if -mvrsave is added to the
> ABI_FLAGS (follow up patch).

Great. I think this is important and valuable information.

Chris