Re: csky: smp_mb__after_spinlock

[Guo Ren]

Hi Peter,

On Thu, Aug 6, 2020 at 3:53 AM <peterz@xxxxxxxxxxxxx> wrote:
>
> Hi,
>
> While doing an audit of smp_mb__after_spinlock, I found that csky
> defines it, why?
>
> CSKY only has smp_mb(), it doesn't override __atomic_acquire_fence or
> otherwise special cases it's atomic*_acquire() primitives. It has an
> explicit smp_mb() in its arch_spin_lock().

Yes, csky didn't implement ACQUIRE/RELEASE in spinlock.h. So it is a
redundant and side-effect wrong macro, we should remove it to fixup.

TODO:
 - implement csky's ACQUIRE/RELEASE barrier

> Also, why have two implementations of all the locking?

I just kept my baby's codes :P. Now, we could remove it and just keep
the ticket's one.

BTW, I want to change the spinlock to qspinlock, but csky only has
32-bit atomic operation in hardware.

Any plan to deal with this in spinlock?

Maybe for the embedded scenario, qspinlock seems a bit heavy, are any
tickets-like comm spinlock infrastructures in the plan?

--
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/