Re: [Qemu-devel] [PATCH 24/58] PPC: E500: Add PV spinning code

[Scott Wood]

On 09/19/2011 06:35 AM, Alexander Graf wrote:
> 
> On 17.09.2011, at 19:40, Blue Swirl wrote:
> 
>> On Sat, Sep 17, 2011 at 5:15 PM, Alexander Graf <address@hidden> wrote:
>>>
>>> Am 17.09.2011 um 18:58 schrieb Blue Swirl <address@hidden>:
>>>
>>>> On Sparc32, there is no need for a PV device. The CPU is woken up from
>>>> halted state with an IPI. Maybe you could use this approach?
>>>
>>> The way it's done here is defined by u-boot and now also nailed down in the 
>>> ePAPR architecture spec. While alternatives might be more appealing, this 
>>> is how guests work today :).
>>
>> OK. I hoped that there were no implementations yet. The header (btw
>> missing) should point to the spec.

The goal with the spin table stuff, suboptimal as it is, was something
that would work on any powerpc implementation.  Other
implementation-specific release mechanisms are allowed, and are
indicated by a property in the cpu node, but only if the loader knows
that the OS supports it.

> IIUC the spec that includes these bits is not finalized yet. It is however in 
> use on all u-boot versions for e500 that I'm aware of and the method Linux 
> uses to bring up secondary CPUs.

It's in ePAPR 1.0, which has been out for a while now.  ePAPR 1.1 was
just released which clarifies some things such as WIMG.

> Stuart / Scott, do you have any pointers to documentation where the spinning 
> is explained?

https://www.power.org/resources/downloads/Power_ePAPR_APPROVED_v1.1.pdf

-Scott