From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753406Ab2AUI3V (ORCPT ); Sat, 21 Jan 2012 03:29:21 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:50858 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751109Ab2AUI3U (ORCPT ); Sat, 21 Jan 2012 03:29:20 -0500 Date: Sat, 21 Jan 2012 09:28:57 +0100 From: Ingo Molnar To: Linus Torvalds , Hitoshi Mitake Cc: Matthew Wilcox , Roland Dreier , Andrew Morton , Hitoshi Mitake , James Bottomley , linux-kernel@vger.kernel.org, linux-nvme@infradead.org, hpa@linux.intel.com Subject: Re: [PATCH] NVMe: Fix compilation on architecturs without readq/writeq Message-ID: <20120121082857.GC32134@elte.hu> References: <1327021265-22184-1-git-send-email-matthew.r.wilcox@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Linus Torvalds wrote: > On Thu, Jan 19, 2012 at 5:01 PM, Matthew Wilcox > wrote: > > The only places that uses readq/writeq are in the initialisation > > path.  Since they're not performance critical, always use readl/writel. > > The arch rules are that i fthe architecture has readq/writeq, they > will be #define'd (they may be inline functions, but there will be a > > #define readq readq > > to make it visible to the preprocessor as well). > > So if you don't need the atomicity guarantees of a "real" readq, you > can do this instead: > > #ifndef readq > static inline u64 readq(void __iomem *addr) > { > return readl(addr) | (((u64) readl(addr + 4)) << 32LL); > } > #endif > > and then use readq() as if it existed. > > And I do think we should expose this in some generic manner. Because > we currently don't, we already have that pattern copied in quite a few > drivers. > > Maybe or something? Making it > clear that its not atomic, but avoiding the silly duplication > we do now.. > > This whole mess was introduced in commit dbee8a0affd5 ("x86: > remove 32-bit versions of readq()/writeq()"), and it already > talked about the problems but didn't help with the drivers > that simply don't care. > > All the people in those threads were doing their > self-satisfied "writeq is broken", without much acknowledging > that 99% of users simply don't seem to care. > > "Occupy Writeq - We are the 99%" Agreed, and offering a generic facility for silly duplication was the motivation of the original commit by Hitoshi Mitake. This: | The presense of a writeq() implementation on 32-bit x86 that | splits the 64-bit write into two 32-bit writes turns out to | break the mpt2sas driver (and in general is risky for drivers | as was discussed in | ). is actually a mostly bogus statement and creates more problems than it solves. Hitoshi-san, would you be interested in re-adding the generic readq/writeq definitions in a slight variation to 2c5643b1c5, to a separate io-nonatomic.h file, so that drivers that want it can #include that file and be happy? Thanks, Ingo