svn commit: r252965 - head/sys/mips/include

Warner Losh imp at
Sun Jul 7 16:12:22 UTC 2013

Author: imp
Date: Sun Jul  7 16:12:22 2013
New Revision: 252965

  Remove all the NOPs after SYNC. They aren't needed.
  They originated in the original Octeon port. They weren't present, as
  far as I can tell, on the projects/mips branch until after this
  point. They were in the original Octeon port in code picked up from
  the vendor, who I've been able to find out trolling old email put them
  there to get around an SMP problem that most likely was fixed in other
  NetBSD and Linux don't have these, except for some specific uses of
  SYNC on the alchemy parts (which we don't support, but even if we did
  it is only a specific case and would be specifically coded
  anyway). This is true of the current Linux code, as well as one old
  version I polled.
  I looked back at the old R12000, R8000, R6000, R4000, R4400 errata
  that I have, and could find no mention of SYNC needing NOPs for
  silicon bugs (although plenty of other cases where NOPs and other
  contortions were needed).
  An Google search turned up no old mailing list discussions on this on
  Linux, NetBSD or FreeBSD (except the disussion that kicked off these
  I've test booted this on my Octeon Plus eval board and survived a
  buildworld. Adrian Chadd reports that this patch has no ill effects on
  the Ahteros platforms he tested it on.
  I conclude it is safe to just remove the NOPs. But added
  __MIPS_PLATFORM_SYNC_NOPS as a failsafe in case we find some platform
  where these are, in fact, required.
  Reviewed by:	adrian@


Modified: head/sys/mips/include/atomic.h
--- head/sys/mips/include/atomic.h	Sun Jul  7 16:11:13 2013	(r252964)
+++ head/sys/mips/include/atomic.h	Sun Jul  7 16:12:22 2013	(r252965)
@@ -44,20 +44,16 @@
  * do not have atomic operations defined for them, but generally shouldn't
  * need atomic operations.
 static __inline  void
-	__asm __volatile (".set noreorder\n\t"
-			"sync\n\t"
-			"nop\n\t"
-			"nop\n\t"
-			"nop\n\t"
-			"nop\n\t"
-			"nop\n\t"
-			"nop\n\t"
-			"nop\n\t"
-			"nop\n\t"
+	__asm __volatile (".set noreorder\n"
+			"\tsync\n"
 			".set reorder\n"
 			: : : "memory");

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