[U-Boot] driver model is not smp safe

[Andrew Bradford]

Hi Bin,

On 07/30 12:12, 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.
> 
> What does this mean?
> 
> -  Driver model is not smp safe. But given U-Boot is a single-threaded
> environment, I don't think we want to add such support to driver
> model.
> 
> OR:
> 
> - We are using driver model incorrectly on x86 mp initialization codes.
> 
> What do you think?

I'm not sure what to do about this (if anything) but I also see this on
an E3845 based board.  I don't think it has affected me in any way.

Does this also affect non-x86 processors?

=> cpu list
  0: cpu at 0              Intel(R) Atom(TM) CPU  E3845  @ 1.91GHz
  2: cpu at 1              Intel(R) Atom(TM) CPU  E3845  @ 1.91GHz
  2: cpu at 2              Intel(R) Atom(TM) CPU  E3845  @ 1.91GHz
  1: cpu at 3              Intel(R) Atom(TM) CPU  E3845  @ 1.91GHz

Thanks,
Andrew