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References: <20220319035457.2214979-1-guoren@kernel.org> <20220319035457.2214979-2-guoren@kernel.org>
In-Reply-To: <20220319035457.2214979-2-guoren@kernel.org>
From:   Arnd Bergmann <arnd@arndb.de>
Date:   Sat, 19 Mar 2022 12:52:09 +0100
Message-ID: <CAK8P3a3wMJv6-fGo_i4DnFMigj=ko4DN1XTe8oa1HzWLiX50yw@mail.gmail.com>
Subject: Re: [PATCH V2 1/5] asm-generic: ticket-lock: New generic ticket-based spinlock
To:     Guo Ren <guoren@kernel.org>
Cc:     Palmer Dabbelt <palmer@dabbelt.com>, Arnd Bergmann <arnd@arndb.de>,
        Boqun Feng <boqun.feng@gmail.com>,
        Waiman Long <longman@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        linux-csky@vger.kernel.org,
        Openrisc <openrisc@lists.librecores.org>,
        Palmer Dabbelt <palmer@rivosinc.com>
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On Sat, Mar 19, 2022 at 4:54 AM <guoren@kernel.org> wrote:
>  /*
> - * You need to implement asm/spinlock.h for SMP support. The generic
> - * version does not handle SMP.
> + * Using ticket-spinlock.h as generic for SMP support.
>   */
>  #ifdef CONFIG_SMP
> -#error need an architecture specific asm/spinlock.h
> +#include <asm-generic/ticket-lock.h>
> +#ifdef CONFIG_QUEUED_RWLOCKS
> +#include <asm-generic/qrwlock.h>
> +#else
> +#error Please select ARCH_USE_QUEUED_RWLOCKS in architecture Kconfig
> +#endif
>  #endif

There is no need for the !CONFIG_SMP case, as asm/spinlock.h only ever
gets included for SMP builds in the first place. This was already a mistake
in the existing code, but your change would be the time to fix it.

I would also drop the !CONFIG_QUEUED_RWLOCKS case, just include
it unconditionally. If any architecture wants the ticket spinlock in
combination with a custom rwlock, they can simply include the
asm-generic/ticket-lock.h from their asm/spinlock.h, but more
likely any architecture that can use the ticket spinlock will also
want the qrwlock anyway.

     Arnd