Re: [PATCH v5 4/7] powerpc/qspinlock: Add ARCH_USE_QUEUED_SPINLOCKS_XCHG32

[Guo Ren]

On Sun, Mar 28, 2021 at 7:14 PM Christophe Leroy
<christophe.leroy@xxxxxxxxxx> wrote:
>
>
>
> Le 28/03/2021 à 08:30, guoren@xxxxxxxxxx a écrit :
> > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> >
> > We don't have native hw xchg16 instruction, so let qspinlock
> > generic code to deal with it.
>
> We have lharx/sthcx pair on some versions of powerpc.
>
> See https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20201107032328.2454582-1-npiggin@xxxxxxxxx/
Got it, thx for the information.

>
> Christophe
>
> >
> > Using the full-word atomic xchg instructions implement xchg16 has
> > the semantic risk for atomic operations.
> >
> > This patch cancels the dependency of on qspinlock generic code on
> > architecture's xchg16.
> >
> > Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> > Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> > Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Paul Mackerras <paulus@xxxxxxxxx>
> > ---
> >   arch/powerpc/Kconfig | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > index 386ae12d8523..69ec4ade6521 100644
> > --- a/arch/powerpc/Kconfig
> > +++ b/arch/powerpc/Kconfig
> > @@ -151,6 +151,7 @@ config PPC
> >       select ARCH_USE_CMPXCHG_LOCKREF         if PPC64
> >       select ARCH_USE_QUEUED_RWLOCKS          if PPC_QUEUED_SPINLOCKS
> >       select ARCH_USE_QUEUED_SPINLOCKS        if PPC_QUEUED_SPINLOCKS
> > +     select ARCH_USE_QUEUED_SPINLOCKS_XCHG32 if PPC_QUEUED_SPINLOCKS
> >       select ARCH_WANT_IPC_PARSE_VERSION
> >       select ARCH_WANT_IRQS_OFF_ACTIVATE_MM
> >       select ARCH_WANT_LD_ORPHAN_WARN
> >



-- 
Best Regards
 Guo Ren

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