[PATCH] powerpc: Add support for VRSAVE

[Sebastian Huber]

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.

> 
> 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).

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