linux-kernel - Re: [PATCH v3 05/11] riscv: Implement arch

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Message-ID: <20240718-stammer-envy-f77637a8d039@wendy>
Date: Thu, 18 Jul 2024 09:33:17 +0100
From: Conor Dooley <conor.dooley@...rochip.com>
To: Alexandre Ghiti <alexghiti@...osinc.com>
CC: Andrew Jones <ajones@...tanamicro.com>, Jonathan Corbet <corbet@....net>,
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
	<palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Conor Dooley
	<conor@...nel.org>, Rob Herring <robh@...nel.org>, Krzysztof Kozlowski
	<krzk+dt@...nel.org>, Andrea Parri <parri.andrea@...il.com>, Nathan
 Chancellor <nathan@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Ingo
 Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>, Waiman Long
	<longman@...hat.com>, Boqun Feng <boqun.feng@...il.com>, Arnd Bergmann
	<arnd@...db.de>, Leonardo Bras <leobras@...hat.com>, Guo Ren
	<guoren@...nel.org>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
	<linux-arch@...r.kernel.org>
Subject: Re: [PATCH v3 05/11] riscv: Implement arch_cmpxchg128() using Zacas

On Thu, Jul 18, 2024 at 09:48:42AM +0200, Alexandre Ghiti wrote:
> On Wed, Jul 17, 2024 at 10:34 PM Andrew Jones <ajones@...tanamicro.com> wrote:
> > On Wed, Jul 17, 2024 at 08:19:51AM GMT, Alexandre Ghiti wrote:
> > > +
> > > +union __u128_halves {
> > > +     u128 full;
> > > +     struct {
> > > +             u64 low, high;
> >
> > Should we consider big endian too?
> 
> Should we care about big endian? We don't deal with big endian
> anywhere in our kernel right now.

There's one or two places I think that we do actually have some
conditional stuff for BE. The Zbb string routines I believe is one such
place, and maybe there are one or two others. In general I'm not of the
opinion that it is worth adding complexity for BE until there's
linux-capable hardware that supports it (so not QEMU or people's toy
implementations), unless it's something that userspace is able to see.


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