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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 26 Aug 2022 16:10:01 -0700
Message-ID: <CAHk-=whO2sd233T8AXNMhYztPiF9hae+1ePOX1fEMEu6Ow1CQQ@mail.gmail.com>
Subject: Re: [PATCH] provide arch_test_bit_acquire for architectures that
 define test_bit
To:     Mikulas Patocka <mpatocka@redhat.com>
Cc:     Brian Cain <bcain@quicinc.com>, linux-hexagon@vger.kernel.org,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Alan Stern <stern@rowland.harvard.edu>,
        Andrea Parri <parri.andrea@gmail.com>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        David Howells <dhowells@redhat.com>,
        Jade Alglave <j.alglave@ucl.ac.uk>,
        Luc Maranget <luc.maranget@inria.fr>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Akira Yokosawa <akiyks@gmail.com>,
        Daniel Lustig <dlustig@nvidia.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-Arch <linux-arch@vger.kernel.org>
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On Fri, Aug 26, 2022 at 1:43 PM Mikulas Patocka <mpatocka@redhat.com> wrote:
>
> I'm wondering why do the architectures redefine test_bit, if their
> definition is equivalent to the generic one? We could just delete
> arch_test_bit and use "#define arch_test_bit generic_test_bit" as well.

I think generic_test_bit() came after many of them, and when it
didn't, people copied earlier architectures where they had already
done their own.

> Another untested patch ... tomorrow, I'll try to compile it, at least for
> architectures where Debian provides cross-compiling gcc.

Looks good to me, except I'd just do

#define arch_test_bit_acquire arch_test_bit

on hexagon rather than duplicate that function.

From my reading, Hexagon doesn't have any fancy memory ordering, it's
just the usual UP with barriers basically for instruction cache
coherence etc.

                 Linus