linux-kernel - Re: [PATCH V2 11/19] csky: Atomic operations

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Message-ID: <20180706114812.GC27148@guoren>
Date:   Fri, 6 Jul 2018 19:48:12 +0800
From:   Guo Ren <ren_guo@...ky.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, daniel.lezcano@...aro.org,
        jason@...edaemon.net, arnd@...db.de, c-sky_gcc_upstream@...ky.com,
        gnu-csky@...tor.com, thomas.petazzoni@...tlin.com,
        wbx@...ibc-ng.org, green.hu@...il.com
Subject: Re: [PATCH V2 11/19] csky: Atomic operations

On Thu, Jul 05, 2018 at 08:00:08PM +0200, Peter Zijlstra wrote:
> On Mon, Jul 02, 2018 at 01:30:14AM +0800, Guo Ren wrote:
> > +#ifdef CONFIG_CPU_HAS_LDSTEX
> > +ENTRY(csky_cmpxchg)
> > +	USPTOKSP
> > +	mfcr	a3, epc
> > +	INCTRAP	a3
> > +
> > +	subi    sp, 8
> > +	stw     a3, (sp, 0)
> > +	mfcr    a3, epsr
> > +	stw     a3, (sp, 4)
> > +
> > +	psrset	ee
> > +1:
> > +	ldex	a3, (a2)
> > +	cmpne	a0, a3
> > +	bt16	2f
> > +	mov	a3, a1
> > +	stex	a3, (a2)
> > +	bez	a3, 1b
> > +2:
> > +	sync.is
> > +	mvc	a0
> > +	ldw	a3, (sp, 0)
> > +	mtcr	a3, epc
> > +	ldw     a3, (sp, 4)
> > +	mtcr	a3, epsr
> > +	addi	sp, 8
> > +	KSPTOUSP
> > +	rte
> > +END(csky_cmpxchg)
> > +#else
> 
> Please explain... if the CPU has LDEX/STEX, then _why_ do you need this?
Our libc use csky_cmpxchg and we want it compatible. Of course, we'll
also implement the ldex/stex atomic operations in libs in future.

 Guo Ren