[U-Boot] driver model is not smp safe

[Simon Glass]

Hi Tom,

On 3 August 2015 at 13:06, Tom Rini <trini at konsulko.com> wrote:
> On Mon, Aug 03, 2015 at 12:52:19PM -0600, Simon Glass wrote:
>> Hi Tom,
>>
>> On 31 July 2015 at 08:31, Tom Rini <trini at konsulko.com> wrote:
>> > On Thu, Jul 30, 2015 at 12:12:03PM +0800, Bin Meng wrote:
>> >
>> >> Hi Simon,
>> >>
>> >> When adding x86 multi-cpu initialization on a board with 4 cores, I found:
>> >>
>> >> => cpu list
>> >>   0: cpu at 0               Genuine Intel(R) CPU         @ 1.58GHz
>> >>   1: cpu at 1               Genuine Intel(R) CPU         @ 1.58GHz
>> >>   2: cpu at 2               Genuine Intel(R) CPU         @ 1.58GHz
>> >>   2: cpu at 3               Genuine Intel(R) CPU         @ 1.58GHz
>> >>
>> >> cpu at 2 and cpu at 3 have the same sequence number, which indicates they
>> >> are running parallelly to get the same sequence number. The call chain
>> >> on an ap is: mp_init_cpu() -> device_probe() -> uclass_resolve_seq().
>> >> Apparently ap2 and ap3 are running at the same time to get the same
>> >> number.
>> >>
>> >> Note so far all x86 boards that we have enabled x86 multi-cpu
>> >> initialization on only have 2 cores, which will not expose such issue
>> >> as there is no parallel execution among aps.
>> >
>> > So what exactly are we doing with these additional cores?  My
>> > recollection of what we do on other arches when we even deal with other
>> > cores is that we bring them "up" and then usually put them in a holding
>> > pattern for the real OS to deal with _or_ it's one of those cases where
>> > we have multiple OSes running and we do what we need to load and release
>> > those other OSes.
>>
>> In this case they end up at stop_this_cpu() which is just a hlt
>> instruction in each case.
>
> So do we really have to be doing anything here?  Or is this just
> pre-emptive work for an async MP type setup down the road?  We could
> probably live with this with a big comment noting why we know it's
> misbehaving.

I think we should fix it - I suggested some options above and Bin may
have ideas also. Bin may be able to send a patch since he can repeat
the problem.

Regards,
Simon