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

On Fri, Jul 06, 2018 at 07:48:12PM +0800, Guo Ren wrote:

On Thu, Jul 05, 2018 at 08:00:08PM +0200, Peter Zijlstra wrote:

quoted

On Mon, Jul 02, 2018 at 01:30:14AM +0800, Guo Ren wrote:

quoted

+#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.

I would strongly suggest not providing this syscall on SMP systems from
the get go. There is no point in starting with legacy problems without
an actual legacy.