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Date:   Tue, 6 Apr 2021 17:51:10 +0900
From:   Stafford Horne <shorne@gmail.com>
To:     Guo Ren <guoren@kernel.org>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-csky@vger.kernel.org,
        linux-arch <linux-arch@vger.kernel.org>,
        Guo Ren <guoren@linux.alibaba.com>,
        Will Deacon <will@kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Waiman Long <longman@redhat.com>,
        Anup Patel <anup@brainfault.org>
Subject: Re: [PATCH v4 3/4] locking/qspinlock: Add
 ARCH_USE_QUEUED_SPINLOCKS_XCHG32
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On Wed, Mar 31, 2021 at 11:10:53PM +0800, Guo Ren wrote:
> Hi Stafford,
> 
> How do think add ARCH_USE_QUEUED_SPINLOCKS_XCHG32 in openrisc?
> 
> https://lore.kernel.org/linux-riscv/1617201040-83905-7-git-send-email-guoren@kernel.org/T/#u

Sorry I missed your mail here.

It is true that OpenRISC doesn't have xchg16, so using the xchg32 code is better.

Acked-by: Stafford Horne <shorne@gmail.com>


> On Wed, Mar 31, 2021 at 8:31 PM Stafford Horne <shorne@gmail.com> wrote:
> >
> > On Wed, Mar 31, 2021 at 09:23:27AM +0200, Arnd Bergmann wrote:
> > > On Wed, Mar 31, 2021 at 12:35 AM Stafford Horne <shorne@gmail.com> wrote:
> > > >
> > > > I just want to chime in here, there may be a better spot in the thread to
> > > > mention this but, for OpenRISC I did implement some generic 8/16-bit xchg code
> > > > which I have on my todo list somwhere to replace the other generic
> > > > implementations like that in mips.
> > > >
> > > >   arch/openrisc/include/asm/cmpxchg.h
> > > >
> > > > The idea would be that architectures just implement these methods:
> > > >
> > > >   long cmpxchg_u32(*ptr,old,new)
> > > >   long xchg_u32(*ptr,val)
> > > >
> > > > Then the rest of the generic header would implement cmpxchg.
> > >
> > > I like the idea of generalizing it a little further. I'd suggest staying a
> > > little closer to the existing naming here though, as we already have
> > > cmpxchg() for the type-agnostic version, and cmpxchg64() for the
> > > fixed-length 64-bit version.
> >
> > OK.
> >
> > > I think a nice interface between architecture-specific and architecture
> > > independent code would be to have architectures provide
> > > arch_cmpxchg32()/arch_xchg32() as the most basic version, as well
> > > as arch_cmpxchg8()/arch_cmpxchg16()/arch_xchg8()/arch_xchg16()
> > > if they have instructions for those.
> >
> > Thanks for the name suggestions, it makes it easier for me.
> >
> > > The common code can then build cmpxchg16()/xchg16() on top of
> > > either the 16-bit or the 32-bit primitives, and build the cmpxchg()/xchg()
> > > wrapper around those (or alternatively we can decide to have them
> > > only deal with fixed-32-bit and long/pointer sized atomics).
> >
> > Yeah, that was the idea.
> >
> > -Stafford
> 
> 
> 
> -- 
> Best Regards
>  Guo Ren
> 
> ML: https://lore.kernel.org/linux-csky/