Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758464Ab3EFUxe (ORCPT ); Mon, 6 May 2013 16:53:34 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:52140 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932066Ab3EFUxc (ORCPT ); Mon, 6 May 2013 16:53:32 -0400 Date: Mon, 6 May 2013 21:53:30 +0100 From: Al Viro To: Matt Turner Cc: Will Deacon , linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, Richard Henderson , Ivan Kokshaysky Subject: Re: [PATCH] alpha: spinlock: don't perform memory access in locked critical section Message-ID: <20130506205329.GO25399@ZenIV.linux.org.uk> References: <1367870465-23948-1-git-send-email-will.deacon@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1466 Lines: 30 On Mon, May 06, 2013 at 01:19:51PM -0700, Matt Turner wrote: > I'm not sure of the interpretation that LDA counts as a memory access. > > The manual says it's Ra <- Rbv + SEXT(disp). > > It's not touching memory that I can see. More to the point, the same manual gives explicit list of instructions that shouldn't occur between LDx_L and STx_C, and LDA does not belong to any of those. I suspect that Will has misparsed the notations in there - LDx is present in the list, but it's _not_ "all instructions with mnemonics starting with LD", just the 4 "load integer from memory" ones. FWIW, instructions with that encoding (x01xxx) are grouped so: LDAx - LDA, LDAH; load address LDx - LDL, LDQ, LDBU, LDWU; load memory data into integer register LDQ_U; load unaligned LDx_L - LDL_L, LDQ_L; load locked STx_C - STL_C, STQ_C; store conditional STx - STL, STQ, STB, STW; store STQ_U; store unaligned They all have the same encoding, naturally enough (operation/register/address representation), but that's it... See section 4.2 in reference manual for details; relevant note follows discussion of LDx_L and it spells the list out. LDx is present, LDAx isn't (and neither is LDA by itself). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/