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    SubjectRe: [RFC][PATCH 14/31] locking,metag: Implement atomic_fetch_{add,sub,and,or,xor}()
    On Sat, Apr 30, 2016 at 01:20:31AM +0100, James Hogan wrote:
    > > + asm volatile ( \
    > > + "1: LNKGETD %1, [%2]\n" \
    > > + " " #op " %0, %1, %3\n" \
    >
    > i was hoping never to have to think about meta asm constraints again :-P

    There is a solution for that: rm -rf arch/metag :-)

    > and/or/xor are only available in the data units, as determined by %1 in
    > this case, so the constraint for result shouldn't have "a" in it.
    >
    > diff --git a/arch/metag/include/asm/atomic_lnkget.h b/arch/metag/include/asm/atomic_lnkget.h
    > index 50ad05050947..def2c642f053 100644
    > --- a/arch/metag/include/asm/atomic_lnkget.h
    > +++ b/arch/metag/include/asm/atomic_lnkget.h
    > @@ -84,7 +84,7 @@ static inline int atomic_fetch_##op(int i, atomic_t *v) \
    > " ANDT %0, %0, #HI(0x3f000000)\n" \
    > " CMPT %0, #HI(0x02000000)\n" \
    > " BNZ 1b\n" \
    > - : "=&d" (temp), "=&da" (result) \
    > + : "=&d" (temp), "=&d" (result) \
    > : "da" (&v->counter), "bd" (i) \
    > : "cc"); \
    >
    > That also ensures the "bd" constraint for %3 (meaning "an op2 register
    > where op1 [%1 in this case] is a data unit register and the instruction
    > supports O2R") is consistent.
    >
    > So with that change this patch looks good to me:

    Right, so I'd _never_ have thought to look at that,

    > Acked-by: James Hogan <james.hogan@imgtec.com>

    Thanks!

    > Note that for the ATOMIC_OP_RETURN() case (add/sub only) either address
    > or data units can be used (hence the "da" for %1), but then the "bd"
    > constraint on %3 is wrong as op1 [%1] may not be in data unit (sorry I
    > didn't spot that at the time). I'll queue a fix, something like below
    > probably ("br" means "An Op2 register and the instruction supports O2R",
    > i.e. op1/%1 doesn't have to be a data unit register):
    >
    > diff --git a/arch/metag/include/asm/atomic_lnkget.h b/arch/metag/include/asm/atomic_lnkget.h
    > index 50ad05050947..def2c642f053 100644
    > --- a/arch/metag/include/asm/atomic_lnkget.h
    > +++ b/arch/metag/include/asm/atomic_lnkget.h
    > @@ -61,7 +61,7 @@ static inline int atomic_##op##_return(int i, atomic_t *v) \
    > " CMPT %0, #HI(0x02000000)\n" \
    > " BNZ 1b\n" \
    > : "=&d" (temp), "=&da" (result) \
    > - : "da" (&v->counter), "bd" (i) \
    > + : "da" (&v->counter), "br" (i) \
    > : "cc"); \
    > \
    > smp_mb(); \
    > \ \

    Thanks, again :-)

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