Received-SPF: pass (google.com: domain of linux-kernel+bounces-193678-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Precedence: bulk
MIME-Version: 1.0
References: <20240528151052.313031-1-alexghiti@rivosinc.com>
 <20240528151052.313031-5-alexghiti@rivosinc.com> <ZlYbupL5XgzgA0MX@andrea>
In-Reply-To: <ZlYbupL5XgzgA0MX@andrea>
From: Alexandre Ghiti <alexghiti@rivosinc.com>
Date: Wed, 29 May 2024 10:04:14 +0200
Message-ID: <CAHVXubgBDxyow3-CFwBrkJ7xoAXCv8Tq7nNTAcvbzbA=TAaf5A@mail.gmail.com>
Subject: Re: [PATCH 4/7] riscv: Implement xchg8/16() using Zabha
To: Andrea Parri <parri.andrea@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>, Paul Walmsley <paul.walmsley@sifive.com>, 
	Palmer Dabbelt <palmer@dabbelt.com>, Albert Ou <aou@eecs.berkeley.edu>, 
	Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>, 
	Waiman Long <longman@redhat.com>, Boqun Feng <boqun.feng@gmail.com>, Arnd Bergmann <arnd@arndb.de>, 
	Leonardo Bras <leobras@redhat.com>, Guo Ren <guoren@kernel.org>, linux-doc@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, 
	linux-arch@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Hi Andrea,

On Tue, May 28, 2024 at 8:00=E2=80=AFPM Andrea Parri <parri.andrea@gmail.co=
m> wrote:
>
> > -#define __arch_xchg_masked(prepend, append, r, p, n)                 \
> > +#define __arch_xchg_masked(swap_sfx, prepend, append, r, p, n)        =
       \
>
> This actually indicates a problem in the current (aka, no Zabha)
> implementation: without your series, xchg16() gets mapped to
>
>   lr.w     a2,(a3)
>   and      a1,a2,a5
>   or       a1,a1,a4
>   sc.w     a1,a1,(a3)
>   bnez     a1,43c <.L0^B1>
>
> which is clearly wrong... (other "fully-ordered LR/SC sequences"
> instead follow the mapping
>
>   lr.w     a2,(a3)
>   and      a1,a2,a5
>   or       a1,a1,a4
>   sc.w.rl  a1,a1,(a3)
>   bnez     a1,43c <.L0^B1>
>   fence    rw,rw  )
>
> A similar consideration for xchg8().

Ok, I will fix that separately and make it merged in -rc2.

Thanks,

Akex

>
>   Andrea