linux-kernel - Re: [PATCH 13/17] RISC-V: Add include subdirectory

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Message-ID: <20170609081635.mrqnzk3wxwou4nqy@hirez.programming.kicks-ass.net>
Date:   Fri, 9 Jun 2017 10:16:35 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>, olof@...om.net,
        albert@...ive.com, patches@...ups.riscv.org,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH 13/17] RISC-V: Add include subdirectory

On Wed, Jun 07, 2017 at 03:17:27PM +0200, Peter Zijlstra wrote:

> > +static inline void arch_spin_unlock(arch_spinlock_t *lock)
> > +{
> > +	__asm__ __volatile__ (
> > +		"amoswap.w.rl x0, x0, %0"
> > +		: "=A" (lock->lock)
> > +		:: "memory");
> > +}
> > +
> > +static inline int arch_spin_trylock(arch_spinlock_t *lock)
> > +{
> > +	int tmp = 1, busy;
> > +
> > +	__asm__ __volatile__ (
> > +		"amoswap.w.aq %0, %2, %1"
> > +		: "=r" (busy), "+A" (lock->lock)
> > +		: "r" (tmp)
> > +		: "memory");
> > +
> > +	return !busy;
> > +}

One other thing, you need to describe the acquire/release semantics for
your platform. Is the above lock RCpc or RCsc ? If RCpc, you need to
look into adding smp_mb__after_unlock_lock().