Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932194Ab2BBPFl (ORCPT ); Thu, 2 Feb 2012 10:05:41 -0500 Received: from mga01.intel.com ([192.55.52.88]:32938 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932072Ab2BBPFk (ORCPT ); Thu, 2 Feb 2012 10:05:40 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.71,315,1320652800"; d="scan'208";a="119708101" Message-ID: <4F2AA642.1030400@linux.intel.com> Date: Thu, 02 Feb 2012 07:05:38 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:9.0) Gecko/20111222 Thunderbird/9.0 MIME-Version: 1.0 To: James Bottomley CC: Linus Torvalds , Ingo Molnar , Alan Cox , Hitoshi Mitake , Matthew Wilcox , Roland Dreier , Andrew Morton , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] NVMe: Fix compilation on architecturs without readq/writeq References: <20120121082857.GC32134@elte.hu> <20120121165830.GA9216@elte.hu> <20120131115855.5861bad7@pyramind.ukuu.org.uk> <20120131120922.GD32010@elte.hu> <20120131121820.58a1db97@pyramind.ukuu.org.uk> <20120131122339.GG32010@elte.hu> <1328144756.2768.57.camel@dabdike.int.hansenpartnership.com> In-Reply-To: <1328144756.2768.57.camel@dabdike.int.hansenpartnership.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1408 Lines: 32 On 02/01/2012 05:05 PM, James Bottomley wrote: > > Incidentally, the last time this came up was with mpt fusion: for a > write to a 64 bit register, it didn't care about order, but it did care > about interleaving as in if you write one half of a 64 bit register and > then write to another register, the 64 bit register effectively gets > written with zeros in the part you didn't write to, so we had to put a > spin lock in the open coded writeb/w/l/q() to make sure the card didn't > get interleaved writes. > There are always going to be hardware which have specific needs, and for those open-coding makes sense, but the littleendian/bigendian pair is going to cover ~90% of users and make sense to can. I worked myself on a driver (which sadly never shipped) which had an WC window and a UC window... the final write in a series had a completion bit in it and would go to the UC window after setting up a whole chunk of operations in the WC window (writing UC memory flushes WC memory ahead of it.) Thus, the two-part breakdown of writeq() to the UC window had to write the low half to the WC window instead. This is clearly not generic. -hpa -- 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/