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SubjectRe: [PATCH V2 11/19] csky: Atomic operations
On Fri, Jul 06, 2018 at 07:48:12PM +0800, Guo Ren wrote:
> On Thu, Jul 05, 2018 at 08:00:08PM +0200, Peter Zijlstra wrote:
> > On Mon, Jul 02, 2018 at 01:30:14AM +0800, Guo Ren wrote:
> > > +#ifdef CONFIG_CPU_HAS_LDSTEX
> > > +ENTRY(csky_cmpxchg)
> > > + USPTOKSP
> > > + mfcr a3, epc
> > > + INCTRAP a3
> > > +
> > > + subi sp, 8
> > > + stw a3, (sp, 0)
> > > + mfcr a3, epsr
> > > + stw a3, (sp, 4)
> > > +
> > > + psrset ee
> > > +1:
> > > + ldex a3, (a2)
> > > + cmpne a0, a3
> > > + bt16 2f
> > > + mov a3, a1
> > > + stex a3, (a2)
> > > + bez a3, 1b
> > > +2:
> > > + sync.is
> > > + mvc a0
> > > + ldw a3, (sp, 0)
> > > + mtcr a3, epc
> > > + ldw a3, (sp, 4)
> > > + mtcr a3, epsr
> > > + addi sp, 8
> > > + KSPTOUSP
> > > + rte
> > > +END(csky_cmpxchg)
> > > +#else
> >
> > Please explain... if the CPU has LDEX/STEX, then _why_ do you need this?
> Our libc use csky_cmpxchg and we want it compatible. Of course, we'll
> also implement the ldex/stex atomic operations in libs in future.

I would strongly suggest not providing this syscall on SMP systems from
the get go. There is no point in starting with legacy problems without
an actual legacy.


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